Re: Re: [DISCUSS] Introduce Hash Lookup Join

[Jingsong Li]

Thanks Jing,

Looks good~

Best,
Jingsong

On Fri, Jan 21, 2022 at 2:00 PM Lincoln Lee  wrote:
>
> Hi, Jing
>   Glad to hear the agreement on the hint syntax, let's keep going!
>
> Best,
> Lincoln Lee
>
>
> Jing Zhang  于2022年1月20日周四 16:52写道：
>
> > Hi Jingsong,
> > Thanks for the feedback.
> >
> > > Is there a conclusion about naming here? (Maybe I missed something?)
> > Use USE_HASH or some other names. Slightly confusing in the FLIP.
> >
> > 'SHUFFLE_HASH' is final hint name, 'USE_HASH' is rejected. I've updated the
> > FLIP.
> >
> > > And the problem of what to write inside the hint, as mentioned by
> > Lincoln.
> >
> > I agree with Lincolon to only include one 'build' side table name only.
> > Besides, Lookup Join only support dimension table as build table, it does
> > not support left input as build table because Lookup join is always
> > triggered by left side.
> >
> > > I think maybe we can list the grammars of other distributed systems,
> > like Hive Spark(Databricks) Snowflake?
> >
> > I add the grammars of other distributed systems(oracle, spark, impala, SQL
> > Server) in FLIP.
> >
> > [1] Oracle USE_Hash hint
> > 
> > SELECT /*+ USE_HASH(l h) */ *
> >   FROM orders h, order_items l
> >   WHERE l.order_id = h.order_id
> > AND l.order_id > 3500;
> >
> >
> > [2] Spark SHUFFLE_HASH hint
> > <
> > https://docs.databricks.com/spark/latest/spark-sql/language-manual/sql-ref-syntax-qry-select-hints.html
> > >
> > SELECT /*+ SHUFFLE_HASH(t1) */ * FROM t1 INNER JOIN t2 ON t1.key = t2.key;
> >
> >
> > [3] IMPALA SHUFFLE hint
> > 
> > SELECT straight_join weather.wind_velocity, geospatial.altitude
> >   FROM weather JOIN /* +SHUFFLE */ geospatial
> >   ON weather.lat = geospatial.lat AND weather.long = geospatial.long;
> >
> >
> > [4] SQL Server Hash Keyword
> > <
> > https://docs.microsoft.com/en-us/sql/t-sql/queries/hints-transact-sql-join?view=sql-server-ver15
> > >
> > SELECT p.Name, pr.ProductReviewID FROM Production.Product AS p LEFT OUTER
> > HASH JOIN Production.ProductReview AS pr ON p.ProductID = pr.ProductID
> > ORDER
> >  BY ProductReviewID DESC;
> >
> >
> > Hive does not have similar grammars because shuffle join is default join
> > behavior of Hive. it only have map join hint  grammars.
> >
> > I didn't find the similar query hint in Snowflake yet.
> >
> >
> > > About `SHUFFLE_HASH(left_table, right_table)`, one case can be shared:
> >
> > SELECT * FROM left_t
> >   JOIN right_1 ON ...
> >   JOIN right_2 ON ...
> >   JOIN right_3 ON ...
> >
> > What if we want to use shuffle_hash for all three joints?
> >
> > SELECT /*+ SHUFFLE_HASH('left_t', 'right_1', 'right_2', 'right_3') */ ？
> >
> > It does not work, because the left input of the second join is not
> > 'left_t' anymore. It is the output of the first join.
> >
> > Good point.
> > As mentioned before, now SHUFFLE_HASH hint only requires to specify build
> > table name.
> > So in the above case,
> > SELECT /*+ SHUFFLE_HASH('right_1', 'right_2', 'right_3') */
> >   * FROM left_t
> >   JOIN right_1 ON ...
> >   JOIN right_2 ON ...
> >   JOIN right_3 ON
> > It means require shuffle on lookup join which contain dimension table with
> > name as 'right_1' or 'right_2' or 'right_3'.
> >
> > WDYT?
> >
> > Best,
> > Jing Zhang
> >
> > Jingsong Li  于2022年1月20日周四 14:33写道：
> >
> > > Hi Jing,
> > >
> > > Sorry for the late reply!
> > >
> > > Is there a conclusion about naming here? (Maybe I missed something?)
> > > Use USE_HASH or some other names. Slightly confusing in the FLIP.
> > >
> > > And the problem of what to write inside the hint, as mentioned by
> > lincoln.
> > >
> > > I think maybe we can list the grammars of other distributed systems,
> > > like Hive Spark(Databricks) Snowflake?
> > >
> > > Best,
> > > Jingsong
> > >
> > > On Thu, Jan 20, 2022 at 1:56 PM Lincoln Lee 
> > > wrote:
> > > >
> > > > Hi, Jing,
> > > >Sorry for the late reply!  The previous discussion for the hint
> > syntax
> > > > left a minor difference there: whether to use both sides of join table
> > > > names or just one 'build' side table name only. I would prefer the
> > later
> > > > one.
> > > >  Users only need to pass the `build` side table(usually the smaller
> > one)
> > > > into `SHUFFLE_HASH(build_table)` join hint, more concisely than
> > > > `SHUFFLE_HASH(left_table, right_table)`, WDYT?
> > > >
> > > > Best,
> > > > Lincoln Lee
> > > >
> > > >
> > > > Jing Zhang  于2022年1月15日周六 17:22写道：
> > > >
> > > > > Hi all,
> > > > > Thanks for all the feedback so far.
> > > > > If there is no more suggestions, I would like to drive a vote in
> > > Tuesday
> > > > > next week (18 Jan).
> > > > >
> > > > > Best,
> > > > > Jing Zhang
> > > > >
> > > > > Jing Zhang  于2022年1月5日周三 11:33写道：
> > > > >
> > > > > > Hi Francesco,
> > > > > > Thanks a lot for the feedback.
> > > > > >
> > > > > > > does it makes sense for a lookup join 

Re: Re: [DISCUSS] Introduce Hash Lookup Join

[Lincoln Lee]

Hi, Jing
  Glad to hear the agreement on the hint syntax, let's keep going!

Best,
Lincoln Lee


Jing Zhang  于2022年1月20日周四 16:52写道：

> Hi Jingsong,
> Thanks for the feedback.
>
> > Is there a conclusion about naming here? (Maybe I missed something?)
> Use USE_HASH or some other names. Slightly confusing in the FLIP.
>
> 'SHUFFLE_HASH' is final hint name, 'USE_HASH' is rejected. I've updated the
> FLIP.
>
> > And the problem of what to write inside the hint, as mentioned by
> Lincoln.
>
> I agree with Lincolon to only include one 'build' side table name only.
> Besides, Lookup Join only support dimension table as build table, it does
> not support left input as build table because Lookup join is always
> triggered by left side.
>
> > I think maybe we can list the grammars of other distributed systems,
> like Hive Spark(Databricks) Snowflake?
>
> I add the grammars of other distributed systems(oracle, spark, impala, SQL
> Server) in FLIP.
>
> [1] Oracle USE_Hash hint
> 
> SELECT /*+ USE_HASH(l h) */ *
>   FROM orders h, order_items l
>   WHERE l.order_id = h.order_id
> AND l.order_id > 3500;
>
>
> [2] Spark SHUFFLE_HASH hint
> <
> https://docs.databricks.com/spark/latest/spark-sql/language-manual/sql-ref-syntax-qry-select-hints.html
> >
> SELECT /*+ SHUFFLE_HASH(t1) */ * FROM t1 INNER JOIN t2 ON t1.key = t2.key;
>
>
> [3] IMPALA SHUFFLE hint
> 
> SELECT straight_join weather.wind_velocity, geospatial.altitude
>   FROM weather JOIN /* +SHUFFLE */ geospatial
>   ON weather.lat = geospatial.lat AND weather.long = geospatial.long;
>
>
> [4] SQL Server Hash Keyword
> <
> https://docs.microsoft.com/en-us/sql/t-sql/queries/hints-transact-sql-join?view=sql-server-ver15
> >
> SELECT p.Name, pr.ProductReviewID FROM Production.Product AS p LEFT OUTER
> HASH JOIN Production.ProductReview AS pr ON p.ProductID = pr.ProductID
> ORDER
>  BY ProductReviewID DESC;
>
>
> Hive does not have similar grammars because shuffle join is default join
> behavior of Hive. it only have map join hint  grammars.
>
> I didn't find the similar query hint in Snowflake yet.
>
>
> > About `SHUFFLE_HASH(left_table, right_table)`, one case can be shared:
>
> SELECT * FROM left_t
>   JOIN right_1 ON ...
>   JOIN right_2 ON ...
>   JOIN right_3 ON ...
>
> What if we want to use shuffle_hash for all three joints?
>
> SELECT /*+ SHUFFLE_HASH('left_t', 'right_1', 'right_2', 'right_3') */ ？
>
> It does not work, because the left input of the second join is not
> 'left_t' anymore. It is the output of the first join.
>
> Good point.
> As mentioned before, now SHUFFLE_HASH hint only requires to specify build
> table name.
> So in the above case,
> SELECT /*+ SHUFFLE_HASH('right_1', 'right_2', 'right_3') */
>   * FROM left_t
>   JOIN right_1 ON ...
>   JOIN right_2 ON ...
>   JOIN right_3 ON
> It means require shuffle on lookup join which contain dimension table with
> name as 'right_1' or 'right_2' or 'right_3'.
>
> WDYT?
>
> Best,
> Jing Zhang
>
> Jingsong Li  于2022年1月20日周四 14:33写道：
>
> > Hi Jing,
> >
> > Sorry for the late reply!
> >
> > Is there a conclusion about naming here? (Maybe I missed something?)
> > Use USE_HASH or some other names. Slightly confusing in the FLIP.
> >
> > And the problem of what to write inside the hint, as mentioned by
> lincoln.
> >
> > I think maybe we can list the grammars of other distributed systems,
> > like Hive Spark(Databricks) Snowflake?
> >
> > Best,
> > Jingsong
> >
> > On Thu, Jan 20, 2022 at 1:56 PM Lincoln Lee 
> > wrote:
> > >
> > > Hi, Jing,
> > >Sorry for the late reply!  The previous discussion for the hint
> syntax
> > > left a minor difference there: whether to use both sides of join table
> > > names or just one 'build' side table name only. I would prefer the
> later
> > > one.
> > >  Users only need to pass the `build` side table(usually the smaller
> one)
> > > into `SHUFFLE_HASH(build_table)` join hint, more concisely than
> > > `SHUFFLE_HASH(left_table, right_table)`, WDYT?
> > >
> > > Best,
> > > Lincoln Lee
> > >
> > >
> > > Jing Zhang  于2022年1月15日周六 17:22写道：
> > >
> > > > Hi all,
> > > > Thanks for all the feedback so far.
> > > > If there is no more suggestions, I would like to drive a vote in
> > Tuesday
> > > > next week (18 Jan).
> > > >
> > > > Best,
> > > > Jing Zhang
> > > >
> > > > Jing Zhang  于2022年1月5日周三 11:33写道：
> > > >
> > > > > Hi Francesco,
> > > > > Thanks a lot for the feedback.
> > > > >
> > > > > > does it makes sense for a lookup join to use hash distribution
> > whenever
> > > > > is possible by default?
> > > > > I prefer to enable the hash lookup join only find the hint in the
> > query
> > > > > for the following reason:
> > > > > 1. Plan compatibility
> > > > > Add a hash shuffle by default would leads to the change of plan
> > after
> > > > > users upgrade the flink version.
> > > > > Besides, lookup join is 

Re: Re: [DISCUSS] Introduce Hash Lookup Join

[Jing Zhang]

Hi Jingsong,
Thanks for the feedback.

> Is there a conclusion about naming here? (Maybe I missed something?)
Use USE_HASH or some other names. Slightly confusing in the FLIP.

'SHUFFLE_HASH' is final hint name, 'USE_HASH' is rejected. I've updated the
FLIP.

> And the problem of what to write inside the hint, as mentioned by Lincoln.

I agree with Lincolon to only include one 'build' side table name only.
Besides, Lookup Join only support dimension table as build table, it does
not support left input as build table because Lookup join is always
triggered by left side.

> I think maybe we can list the grammars of other distributed systems,
like Hive Spark(Databricks) Snowflake?

I add the grammars of other distributed systems(oracle, spark, impala, SQL
Server) in FLIP.

[1] Oracle USE_Hash hint

SELECT /*+ USE_HASH(l h) */ *
  FROM orders h, order_items l
  WHERE l.order_id = h.order_id
AND l.order_id > 3500;


[2] Spark SHUFFLE_HASH hint

SELECT /*+ SHUFFLE_HASH(t1) */ * FROM t1 INNER JOIN t2 ON t1.key = t2.key;


[3] IMPALA SHUFFLE hint

SELECT straight_join weather.wind_velocity, geospatial.altitude
  FROM weather JOIN /* +SHUFFLE */ geospatial
  ON weather.lat = geospatial.lat AND weather.long = geospatial.long;


[4] SQL Server Hash Keyword

SELECT p.Name, pr.ProductReviewID FROM Production.Product AS p LEFT OUTER
HASH JOIN Production.ProductReview AS pr ON p.ProductID = pr.ProductID ORDER
 BY ProductReviewID DESC;


Hive does not have similar grammars because shuffle join is default join
behavior of Hive. it only have map join hint  grammars.

I didn't find the similar query hint in Snowflake yet.


> About `SHUFFLE_HASH(left_table, right_table)`, one case can be shared:

SELECT * FROM left_t
  JOIN right_1 ON ...
  JOIN right_2 ON ...
  JOIN right_3 ON ...

What if we want to use shuffle_hash for all three joints?

SELECT /*+ SHUFFLE_HASH('left_t', 'right_1', 'right_2', 'right_3') */ ？

It does not work, because the left input of the second join is not
'left_t' anymore. It is the output of the first join.

Good point.
As mentioned before, now SHUFFLE_HASH hint only requires to specify build
table name.
So in the above case,
SELECT /*+ SHUFFLE_HASH('right_1', 'right_2', 'right_3') */
  * FROM left_t
  JOIN right_1 ON ...
  JOIN right_2 ON ...
  JOIN right_3 ON
It means require shuffle on lookup join which contain dimension table with
name as 'right_1' or 'right_2' or 'right_3'.

WDYT?

Best,
Jing Zhang

Jingsong Li  于2022年1月20日周四 14:33写道：

> Hi Jing,
>
> Sorry for the late reply!
>
> Is there a conclusion about naming here? (Maybe I missed something?)
> Use USE_HASH or some other names. Slightly confusing in the FLIP.
>
> And the problem of what to write inside the hint, as mentioned by lincoln.
>
> I think maybe we can list the grammars of other distributed systems,
> like Hive Spark(Databricks) Snowflake?
>
> Best,
> Jingsong
>
> On Thu, Jan 20, 2022 at 1:56 PM Lincoln Lee 
> wrote:
> >
> > Hi, Jing,
> >Sorry for the late reply!  The previous discussion for the hint syntax
> > left a minor difference there: whether to use both sides of join table
> > names or just one 'build' side table name only. I would prefer the later
> > one.
> >  Users only need to pass the `build` side table(usually the smaller one)
> > into `SHUFFLE_HASH(build_table)` join hint, more concisely than
> > `SHUFFLE_HASH(left_table, right_table)`, WDYT?
> >
> > Best,
> > Lincoln Lee
> >
> >
> > Jing Zhang  于2022年1月15日周六 17:22写道：
> >
> > > Hi all,
> > > Thanks for all the feedback so far.
> > > If there is no more suggestions, I would like to drive a vote in
> Tuesday
> > > next week (18 Jan).
> > >
> > > Best,
> > > Jing Zhang
> > >
> > > Jing Zhang  于2022年1月5日周三 11:33写道：
> > >
> > > > Hi Francesco,
> > > > Thanks a lot for the feedback.
> > > >
> > > > > does it makes sense for a lookup join to use hash distribution
> whenever
> > > > is possible by default?
> > > > I prefer to enable the hash lookup join only find the hint in the
> query
> > > > for the following reason:
> > > > 1. Plan compatibility
> > > > Add a hash shuffle by default would leads to the change of plan
> after
> > > > users upgrade the flink version.
> > > > Besides, lookup join is commonly used feature in flink SQL.
> > > > 2. Not all flink jobs could benefit from this improvement.
> > > > It is a trade off for the lookup join with dimension connectors
> which
> > > > has cache inside.
> > > > We hope the raise the cache hit ratio by Hash Lookup Join,
> however it
> > > > would leads to an extra shuffle at the same time.
> > > > It is not always a positive optimization, especially for the
> 

Re: Re: [DISCUSS] Introduce Hash Lookup Join

[Jing Zhang]

Hi Lincoln,

Thanks for the feedback.
> The previous discussion for the hint syntax
left a minor difference there: whether to use both sides of join table
names or just one 'build' side table name only. I would prefer the later
one.
 Users only need to pass the `build` side table(usually the smaller one)
into `SHUFFLE_HASH(build_table)` join hint, more concisely than
`SHUFFLE_HASH(left_table, right_table)`, WDYT?

Make sense.
Besides, Lookup Join only support dimension table as build table, it does
not support left input as build table because Lookup join is always
triggered by left side.
WDYT?

Best,
Jing Zhang



Jingsong Li  于2022年1月20日周四 15:09写道：

> Hi Jing,
>
> About `SHUFFLE_HASH(left_table, right_table)`, one case can be shared:
>
> SELECT * FROM left_t
>   JOIN right_1 ON ...
>   JOIN right_2 ON ...
>   JOIN right_3 ON ...
>
> What if we want to use shuffle_hash for all three joints?
>
> SELECT /*+ SHUFFLE_HASH('left_t', 'right_1', 'right_2', 'right_3') */ ？
>
> It does not work, because the left input of the second join is not
> 'left_t' anymore. It is the output of the first join.
>
> Best,
> Jingsong
>
> On Thu, Jan 20, 2022 at 2:33 PM Jingsong Li 
> wrote:
> >
> > Hi Jing,
> >
> > Sorry for the late reply!
> >
> > Is there a conclusion about naming here? (Maybe I missed something?)
> > Use USE_HASH or some other names. Slightly confusing in the FLIP.
> >
> > And the problem of what to write inside the hint, as mentioned by
> lincoln.
> >
> > I think maybe we can list the grammars of other distributed systems,
> > like Hive Spark(Databricks) Snowflake?
> >
> > Best,
> > Jingsong
> >
> > On Thu, Jan 20, 2022 at 1:56 PM Lincoln Lee 
> wrote:
> > >
> > > Hi, Jing,
> > >Sorry for the late reply!  The previous discussion for the hint
> syntax
> > > left a minor difference there: whether to use both sides of join table
> > > names or just one 'build' side table name only. I would prefer the
> later
> > > one.
> > >  Users only need to pass the `build` side table(usually the smaller
> one)
> > > into `SHUFFLE_HASH(build_table)` join hint, more concisely than
> > > `SHUFFLE_HASH(left_table, right_table)`, WDYT?
> > >
> > > Best,
> > > Lincoln Lee
> > >
> > >
> > > Jing Zhang  于2022年1月15日周六 17:22写道：
> > >
> > > > Hi all,
> > > > Thanks for all the feedback so far.
> > > > If there is no more suggestions, I would like to drive a vote in
> Tuesday
> > > > next week (18 Jan).
> > > >
> > > > Best,
> > > > Jing Zhang
> > > >
> > > > Jing Zhang  于2022年1月5日周三 11:33写道：
> > > >
> > > > > Hi Francesco,
> > > > > Thanks a lot for the feedback.
> > > > >
> > > > > > does it makes sense for a lookup join to use hash distribution
> whenever
> > > > > is possible by default?
> > > > > I prefer to enable the hash lookup join only find the hint in the
> query
> > > > > for the following reason:
> > > > > 1. Plan compatibility
> > > > > Add a hash shuffle by default would leads to the change of
> plan after
> > > > > users upgrade the flink version.
> > > > > Besides, lookup join is commonly used feature in flink SQL.
> > > > > 2. Not all flink jobs could benefit from this improvement.
> > > > > It is a trade off for the lookup join with dimension
> connectors which
> > > > > has cache inside.
> > > > > We hope the raise the cache hit ratio by Hash Lookup Join,
> however it
> > > > > would leads to an extra shuffle at the same time.
> > > > > It is not always a positive optimization, especially for the
> > > > > connectors which does not have cache inside.
> > > > >
> > > > > > Shouldn't the hint take the table alias as the "table name"?
> What if
> > > > > you do two lookup joins in cascade within the same query with the
> same
> > > > > table (once
> > > > > on a key, then on another one), where you use two different
> aliases for
> > > > > the table?
> > > > > In theory, it's better to support both table names and alias names.
> > > > > But in calcite, the alias name of subquery or table would not be
> lost in
> > > > > the sql conversion phase and sql optimization phase.
> > > > > So here we only support table names.
> > > > >
> > > > > Best,
> > > > > Jing Zhang
> > > > >
> > > > >
> > > > > Francesco Guardiani  于2022年1月3日周一
> 18:38写道：
> > > > >
> > > > >> Hi Jing,
> > > > >>
> > > > >> Thanks for the FLIP. I'm not very knowledgeable about the topic,
> but
> > > > going
> > > > >> through both the FLIP and the discussion here, I wonder, does it
> makes
> > > > >> sense for a lookup join to use hash distribution whenever is
> possible by
> > > > >> default?
> > > > >>
> > > > >> The point you're explaining here:
> > > > >>
> > > > >> > Many Lookup table sources introduce cache in order
> > > > >> to reduce the RPC call, such as JDBC, CSV, HBase connectors.
> > > > >> For those connectors, we could raise cache hit ratio by routing
> the same
> > > > >> lookup keys to the same task instance
> > > > >>
> > > > >> Seems something we can infer automatically, rather than manually
> asking
> > > > 

Re: Re: [DISCUSS] Introduce Hash Lookup Join

[Jingsong Li]

Hi Jing,

About `SHUFFLE_HASH(left_table, right_table)`, one case can be shared:

SELECT * FROM left_t
  JOIN right_1 ON ...
  JOIN right_2 ON ...
  JOIN right_3 ON ...

What if we want to use shuffle_hash for all three joints?

SELECT /*+ SHUFFLE_HASH('left_t', 'right_1', 'right_2', 'right_3') */ ？

It does not work, because the left input of the second join is not
'left_t' anymore. It is the output of the first join.

Best,
Jingsong

On Thu, Jan 20, 2022 at 2:33 PM Jingsong Li  wrote:
>
> Hi Jing,
>
> Sorry for the late reply!
>
> Is there a conclusion about naming here? (Maybe I missed something?)
> Use USE_HASH or some other names. Slightly confusing in the FLIP.
>
> And the problem of what to write inside the hint, as mentioned by lincoln.
>
> I think maybe we can list the grammars of other distributed systems,
> like Hive Spark(Databricks) Snowflake?
>
> Best,
> Jingsong
>
> On Thu, Jan 20, 2022 at 1:56 PM Lincoln Lee  wrote:
> >
> > Hi, Jing,
> >Sorry for the late reply!  The previous discussion for the hint syntax
> > left a minor difference there: whether to use both sides of join table
> > names or just one 'build' side table name only. I would prefer the later
> > one.
> >  Users only need to pass the `build` side table(usually the smaller one)
> > into `SHUFFLE_HASH(build_table)` join hint, more concisely than
> > `SHUFFLE_HASH(left_table, right_table)`, WDYT?
> >
> > Best,
> > Lincoln Lee
> >
> >
> > Jing Zhang  于2022年1月15日周六 17:22写道：
> >
> > > Hi all,
> > > Thanks for all the feedback so far.
> > > If there is no more suggestions, I would like to drive a vote in Tuesday
> > > next week (18 Jan).
> > >
> > > Best,
> > > Jing Zhang
> > >
> > > Jing Zhang  于2022年1月5日周三 11:33写道：
> > >
> > > > Hi Francesco,
> > > > Thanks a lot for the feedback.
> > > >
> > > > > does it makes sense for a lookup join to use hash distribution 
> > > > > whenever
> > > > is possible by default?
> > > > I prefer to enable the hash lookup join only find the hint in the query
> > > > for the following reason:
> > > > 1. Plan compatibility
> > > > Add a hash shuffle by default would leads to the change of plan 
> > > > after
> > > > users upgrade the flink version.
> > > > Besides, lookup join is commonly used feature in flink SQL.
> > > > 2. Not all flink jobs could benefit from this improvement.
> > > > It is a trade off for the lookup join with dimension connectors 
> > > > which
> > > > has cache inside.
> > > > We hope the raise the cache hit ratio by Hash Lookup Join, however 
> > > > it
> > > > would leads to an extra shuffle at the same time.
> > > > It is not always a positive optimization, especially for the
> > > > connectors which does not have cache inside.
> > > >
> > > > > Shouldn't the hint take the table alias as the "table name"?  What if
> > > > you do two lookup joins in cascade within the same query with the same
> > > > table (once
> > > > on a key, then on another one), where you use two different aliases for
> > > > the table?
> > > > In theory, it's better to support both table names and alias names.
> > > > But in calcite, the alias name of subquery or table would not be lost in
> > > > the sql conversion phase and sql optimization phase.
> > > > So here we only support table names.
> > > >
> > > > Best,
> > > > Jing Zhang
> > > >
> > > >
> > > > Francesco Guardiani  于2022年1月3日周一 18:38写道：
> > > >
> > > >> Hi Jing,
> > > >>
> > > >> Thanks for the FLIP. I'm not very knowledgeable about the topic, but
> > > going
> > > >> through both the FLIP and the discussion here, I wonder, does it makes
> > > >> sense for a lookup join to use hash distribution whenever is possible 
> > > >> by
> > > >> default?
> > > >>
> > > >> The point you're explaining here:
> > > >>
> > > >> > Many Lookup table sources introduce cache in order
> > > >> to reduce the RPC call, such as JDBC, CSV, HBase connectors.
> > > >> For those connectors, we could raise cache hit ratio by routing the 
> > > >> same
> > > >> lookup keys to the same task instance
> > > >>
> > > >> Seems something we can infer automatically, rather than manually asking
> > > >> the
> > > >> user to add this hint to the query. Note that I'm not talking against
> > > the
> > > >> hint syntax, which might still make sense to be introduced, but I feel
> > > >> like
> > > >> this optimization makes sense in the general case when using the
> > > >> connectors
> > > >> you have quoted. Perhaps there is some downside I'm not aware of?
> > > >>
> > > >> Talking about the hint themselves, taking this example as reference:
> > > >>
> > > >> SELECT /*+ SHUFFLE_HASH('Orders', 'Customers') */ o.order_id, o.total,
> > > >> c.country, c.zip
> > > >> FROM Orders AS o
> > > >> JOIN Customers FOR SYSTEM_TIME AS OF o.proc_time AS c
> > > >> ON o.customer_id = c.id;
> > > >>
> > > >> Shouldn't the hint take the table alias as the "table name"? What If 
> > > >> you
> > > >> do
> > > >> two lookup joins in cascade within the same query with the same 

Re: Re: [DISCUSS] Introduce Hash Lookup Join

[Jingsong Li]

Hi Jing,

Sorry for the late reply!

Is there a conclusion about naming here? (Maybe I missed something?)
Use USE_HASH or some other names. Slightly confusing in the FLIP.

And the problem of what to write inside the hint, as mentioned by lincoln.

I think maybe we can list the grammars of other distributed systems,
like Hive Spark(Databricks) Snowflake?

Best,
Jingsong

On Thu, Jan 20, 2022 at 1:56 PM Lincoln Lee  wrote:
>
> Hi, Jing,
>Sorry for the late reply!  The previous discussion for the hint syntax
> left a minor difference there: whether to use both sides of join table
> names or just one 'build' side table name only. I would prefer the later
> one.
>  Users only need to pass the `build` side table(usually the smaller one)
> into `SHUFFLE_HASH(build_table)` join hint, more concisely than
> `SHUFFLE_HASH(left_table, right_table)`, WDYT?
>
> Best,
> Lincoln Lee
>
>
> Jing Zhang  于2022年1月15日周六 17:22写道：
>
> > Hi all,
> > Thanks for all the feedback so far.
> > If there is no more suggestions, I would like to drive a vote in Tuesday
> > next week (18 Jan).
> >
> > Best,
> > Jing Zhang
> >
> > Jing Zhang  于2022年1月5日周三 11:33写道：
> >
> > > Hi Francesco,
> > > Thanks a lot for the feedback.
> > >
> > > > does it makes sense for a lookup join to use hash distribution whenever
> > > is possible by default?
> > > I prefer to enable the hash lookup join only find the hint in the query
> > > for the following reason:
> > > 1. Plan compatibility
> > > Add a hash shuffle by default would leads to the change of plan after
> > > users upgrade the flink version.
> > > Besides, lookup join is commonly used feature in flink SQL.
> > > 2. Not all flink jobs could benefit from this improvement.
> > > It is a trade off for the lookup join with dimension connectors which
> > > has cache inside.
> > > We hope the raise the cache hit ratio by Hash Lookup Join, however it
> > > would leads to an extra shuffle at the same time.
> > > It is not always a positive optimization, especially for the
> > > connectors which does not have cache inside.
> > >
> > > > Shouldn't the hint take the table alias as the "table name"?  What if
> > > you do two lookup joins in cascade within the same query with the same
> > > table (once
> > > on a key, then on another one), where you use two different aliases for
> > > the table?
> > > In theory, it's better to support both table names and alias names.
> > > But in calcite, the alias name of subquery or table would not be lost in
> > > the sql conversion phase and sql optimization phase.
> > > So here we only support table names.
> > >
> > > Best,
> > > Jing Zhang
> > >
> > >
> > > Francesco Guardiani  于2022年1月3日周一 18:38写道：
> > >
> > >> Hi Jing,
> > >>
> > >> Thanks for the FLIP. I'm not very knowledgeable about the topic, but
> > going
> > >> through both the FLIP and the discussion here, I wonder, does it makes
> > >> sense for a lookup join to use hash distribution whenever is possible by
> > >> default?
> > >>
> > >> The point you're explaining here:
> > >>
> > >> > Many Lookup table sources introduce cache in order
> > >> to reduce the RPC call, such as JDBC, CSV, HBase connectors.
> > >> For those connectors, we could raise cache hit ratio by routing the same
> > >> lookup keys to the same task instance
> > >>
> > >> Seems something we can infer automatically, rather than manually asking
> > >> the
> > >> user to add this hint to the query. Note that I'm not talking against
> > the
> > >> hint syntax, which might still make sense to be introduced, but I feel
> > >> like
> > >> this optimization makes sense in the general case when using the
> > >> connectors
> > >> you have quoted. Perhaps there is some downside I'm not aware of?
> > >>
> > >> Talking about the hint themselves, taking this example as reference:
> > >>
> > >> SELECT /*+ SHUFFLE_HASH('Orders', 'Customers') */ o.order_id, o.total,
> > >> c.country, c.zip
> > >> FROM Orders AS o
> > >> JOIN Customers FOR SYSTEM_TIME AS OF o.proc_time AS c
> > >> ON o.customer_id = c.id;
> > >>
> > >> Shouldn't the hint take the table alias as the "table name"? What If you
> > >> do
> > >> two lookup joins in cascade within the same query with the same table
> > >> (once
> > >> on a key, then on another one), where you use two different aliases for
> > >> the
> > >> table?
> > >>
> > >>
> > >> On Fri, Dec 31, 2021 at 9:56 AM Jing Zhang 
> > wrote:
> > >>
> > >> > Hi Lincoln,
> > >> > Thanks for the feedback.
> > >> >
> > >> > > 1. For the hint name, +1 for WenLong's proposal.
> > >> >
> > >> > I've added add 'SHUFFLE_HASH' to other alternatives in FLIP. Let's
> > >> waiting
> > >> > for more voices here.
> > >> >
> > >> > > Regarding the `SKEW` hint, agree with you that it can be used
> > widely,
> > >> and
> > >> > I
> > >> > prefer to treat it as a metadata hint, a new category differs from a
> > >> join
> > >> > hint.
> > >> > For your example:
> > >> > ```
> > >> > SELECT /*+ USE_HASH('Orders', 'Customers'), 

Re: Re: [DISCUSS] Introduce Hash Lookup Join

[Lincoln Lee]

Hi, Jing,
   Sorry for the late reply!  The previous discussion for the hint syntax
left a minor difference there: whether to use both sides of join table
names or just one 'build' side table name only. I would prefer the later
one.
 Users only need to pass the `build` side table(usually the smaller one)
into `SHUFFLE_HASH(build_table)` join hint, more concisely than
`SHUFFLE_HASH(left_table, right_table)`, WDYT?

Best,
Lincoln Lee


Jing Zhang  于2022年1月15日周六 17:22写道：

> Hi all,
> Thanks for all the feedback so far.
> If there is no more suggestions, I would like to drive a vote in Tuesday
> next week (18 Jan).
>
> Best,
> Jing Zhang
>
> Jing Zhang  于2022年1月5日周三 11:33写道：
>
> > Hi Francesco,
> > Thanks a lot for the feedback.
> >
> > > does it makes sense for a lookup join to use hash distribution whenever
> > is possible by default?
> > I prefer to enable the hash lookup join only find the hint in the query
> > for the following reason:
> > 1. Plan compatibility
> > Add a hash shuffle by default would leads to the change of plan after
> > users upgrade the flink version.
> > Besides, lookup join is commonly used feature in flink SQL.
> > 2. Not all flink jobs could benefit from this improvement.
> > It is a trade off for the lookup join with dimension connectors which
> > has cache inside.
> > We hope the raise the cache hit ratio by Hash Lookup Join, however it
> > would leads to an extra shuffle at the same time.
> > It is not always a positive optimization, especially for the
> > connectors which does not have cache inside.
> >
> > > Shouldn't the hint take the table alias as the "table name"?  What if
> > you do two lookup joins in cascade within the same query with the same
> > table (once
> > on a key, then on another one), where you use two different aliases for
> > the table?
> > In theory, it's better to support both table names and alias names.
> > But in calcite, the alias name of subquery or table would not be lost in
> > the sql conversion phase and sql optimization phase.
> > So here we only support table names.
> >
> > Best,
> > Jing Zhang
> >
> >
> > Francesco Guardiani  于2022年1月3日周一 18:38写道：
> >
> >> Hi Jing,
> >>
> >> Thanks for the FLIP. I'm not very knowledgeable about the topic, but
> going
> >> through both the FLIP and the discussion here, I wonder, does it makes
> >> sense for a lookup join to use hash distribution whenever is possible by
> >> default?
> >>
> >> The point you're explaining here:
> >>
> >> > Many Lookup table sources introduce cache in order
> >> to reduce the RPC call, such as JDBC, CSV, HBase connectors.
> >> For those connectors, we could raise cache hit ratio by routing the same
> >> lookup keys to the same task instance
> >>
> >> Seems something we can infer automatically, rather than manually asking
> >> the
> >> user to add this hint to the query. Note that I'm not talking against
> the
> >> hint syntax, which might still make sense to be introduced, but I feel
> >> like
> >> this optimization makes sense in the general case when using the
> >> connectors
> >> you have quoted. Perhaps there is some downside I'm not aware of?
> >>
> >> Talking about the hint themselves, taking this example as reference:
> >>
> >> SELECT /*+ SHUFFLE_HASH('Orders', 'Customers') */ o.order_id, o.total,
> >> c.country, c.zip
> >> FROM Orders AS o
> >> JOIN Customers FOR SYSTEM_TIME AS OF o.proc_time AS c
> >> ON o.customer_id = c.id;
> >>
> >> Shouldn't the hint take the table alias as the "table name"? What If you
> >> do
> >> two lookup joins in cascade within the same query with the same table
> >> (once
> >> on a key, then on another one), where you use two different aliases for
> >> the
> >> table?
> >>
> >>
> >> On Fri, Dec 31, 2021 at 9:56 AM Jing Zhang 
> wrote:
> >>
> >> > Hi Lincoln,
> >> > Thanks for the feedback.
> >> >
> >> > > 1. For the hint name, +1 for WenLong's proposal.
> >> >
> >> > I've added add 'SHUFFLE_HASH' to other alternatives in FLIP. Let's
> >> waiting
> >> > for more voices here.
> >> >
> >> > > Regarding the `SKEW` hint, agree with you that it can be used
> widely,
> >> and
> >> > I
> >> > prefer to treat it as a metadata hint, a new category differs from a
> >> join
> >> > hint.
> >> > For your example:
> >> > ```
> >> > SELECT /*+ USE_HASH('Orders', 'Customers'), SKEW('Orders') */
> >> o.order_id,
> >> > o.total, c.country, c.zip
> >> > FROM Orders AS o
> >> > JOIN Customers FOR SYSTEM_TIME AS OF o.proc_time AS c
> >> > ON o.customer_id = c.id;
> >> > ```
> >> > I would prefer another form:
> >> > ```
> >> > -- provide the skew info to let the engine choose the optimal plan
> >> > SELECT /*+ SKEW('Orders') */ o.order_id, ...
> >> >
> >> > -- or introduce a new hint for the join case, e.g.,
> >> > SELECT /*+ REPLICATED_SHUFFLE_HASH('Orders') */ o.order_id, ...
> >> > ```
> >> >
> >> > Maybe there is misunderstanding here.
> >> > I just use a syntax sugar here.
> >> >
> >> > SELECT /*+ USE_HASH('Orders', 'Customers'), 

Re: Re: [DISCUSS] Introduce Hash Lookup Join

[Jing Zhang]

Hi all,
Thanks for all the feedback so far.
If there is no more suggestions, I would like to drive a vote in Tuesday
next week (18 Jan).

Best,
Jing Zhang

Jing Zhang  于2022年1月5日周三 11:33写道：

> Hi Francesco,
> Thanks a lot for the feedback.
>
> > does it makes sense for a lookup join to use hash distribution whenever
> is possible by default?
> I prefer to enable the hash lookup join only find the hint in the query
> for the following reason:
> 1. Plan compatibility
> Add a hash shuffle by default would leads to the change of plan after
> users upgrade the flink version.
> Besides, lookup join is commonly used feature in flink SQL.
> 2. Not all flink jobs could benefit from this improvement.
> It is a trade off for the lookup join with dimension connectors which
> has cache inside.
> We hope the raise the cache hit ratio by Hash Lookup Join, however it
> would leads to an extra shuffle at the same time.
> It is not always a positive optimization, especially for the
> connectors which does not have cache inside.
>
> > Shouldn't the hint take the table alias as the "table name"?  What if
> you do two lookup joins in cascade within the same query with the same
> table (once
> on a key, then on another one), where you use two different aliases for
> the table?
> In theory, it's better to support both table names and alias names.
> But in calcite, the alias name of subquery or table would not be lost in
> the sql conversion phase and sql optimization phase.
> So here we only support table names.
>
> Best,
> Jing Zhang
>
>
> Francesco Guardiani  于2022年1月3日周一 18:38写道：
>
>> Hi Jing,
>>
>> Thanks for the FLIP. I'm not very knowledgeable about the topic, but going
>> through both the FLIP and the discussion here, I wonder, does it makes
>> sense for a lookup join to use hash distribution whenever is possible by
>> default?
>>
>> The point you're explaining here:
>>
>> > Many Lookup table sources introduce cache in order
>> to reduce the RPC call, such as JDBC, CSV, HBase connectors.
>> For those connectors, we could raise cache hit ratio by routing the same
>> lookup keys to the same task instance
>>
>> Seems something we can infer automatically, rather than manually asking
>> the
>> user to add this hint to the query. Note that I'm not talking against the
>> hint syntax, which might still make sense to be introduced, but I feel
>> like
>> this optimization makes sense in the general case when using the
>> connectors
>> you have quoted. Perhaps there is some downside I'm not aware of?
>>
>> Talking about the hint themselves, taking this example as reference:
>>
>> SELECT /*+ SHUFFLE_HASH('Orders', 'Customers') */ o.order_id, o.total,
>> c.country, c.zip
>> FROM Orders AS o
>> JOIN Customers FOR SYSTEM_TIME AS OF o.proc_time AS c
>> ON o.customer_id = c.id;
>>
>> Shouldn't the hint take the table alias as the "table name"? What If you
>> do
>> two lookup joins in cascade within the same query with the same table
>> (once
>> on a key, then on another one), where you use two different aliases for
>> the
>> table?
>>
>>
>> On Fri, Dec 31, 2021 at 9:56 AM Jing Zhang  wrote:
>>
>> > Hi Lincoln,
>> > Thanks for the feedback.
>> >
>> > > 1. For the hint name, +1 for WenLong's proposal.
>> >
>> > I've added add 'SHUFFLE_HASH' to other alternatives in FLIP. Let's
>> waiting
>> > for more voices here.
>> >
>> > > Regarding the `SKEW` hint, agree with you that it can be used widely,
>> and
>> > I
>> > prefer to treat it as a metadata hint, a new category differs from a
>> join
>> > hint.
>> > For your example:
>> > ```
>> > SELECT /*+ USE_HASH('Orders', 'Customers'), SKEW('Orders') */
>> o.order_id,
>> > o.total, c.country, c.zip
>> > FROM Orders AS o
>> > JOIN Customers FOR SYSTEM_TIME AS OF o.proc_time AS c
>> > ON o.customer_id = c.id;
>> > ```
>> > I would prefer another form:
>> > ```
>> > -- provide the skew info to let the engine choose the optimal plan
>> > SELECT /*+ SKEW('Orders') */ o.order_id, ...
>> >
>> > -- or introduce a new hint for the join case, e.g.,
>> > SELECT /*+ REPLICATED_SHUFFLE_HASH('Orders') */ o.order_id, ...
>> > ```
>> >
>> > Maybe there is misunderstanding here.
>> > I just use a syntax sugar here.
>> >
>> > SELECT /*+ USE_HASH('Orders', 'Customers'), SKEW('Orders') */
>> o.order_id,
>> > 
>> >
>> > is just a syntax with
>> >
>> > SELECT /*+ USE_HASH('Orders', 'Customers') */ /*+SKEW('Orders') */
>> > o.order_id,
>> > 
>> >
>> > Although I list 'USE_HASH' and 'SKEW' hint in a query hint clause, it
>> does
>> > not mean they must appear together as a whole.
>> > Based on calcite syntax doc [1], you could list more than one hint in
>> > a /*+' hint [, hint ]* '*/ clause.
>> >
>> > Each hint has different function.
>> > The'USE_HASH' hint suggests the optimizer use hash partitioner for
>> Lookup
>> > Join for table 'Orders' and table 'Customers' while the 'SKEW' hint
>> tells
>> > the optimizer the skew metadata about the table 'Orders'.
>> >
>> > Best,
>> > Jing Zhang
>> 

Re: Re: [DISCUSS] Introduce Hash Lookup Join

[Jing Zhang]

Hi Francesco,
Thanks a lot for the feedback.

> does it makes sense for a lookup join to use hash distribution whenever
is possible by default?
I prefer to enable the hash lookup join only find the hint in the query for
the following reason:
1. Plan compatibility
Add a hash shuffle by default would leads to the change of plan after
users upgrade the flink version.
Besides, lookup join is commonly used feature in flink SQL.
2. Not all flink jobs could benefit from this improvement.
It is a trade off for the lookup join with dimension connectors which
has cache inside.
We hope the raise the cache hit ratio by Hash Lookup Join, however it
would leads to an extra shuffle at the same time.
It is not always a positive optimization, especially for the connectors
which does not have cache inside.

> Shouldn't the hint take the table alias as the "table name"?  What if you
do two lookup joins in cascade within the same query with the same table
(once
on a key, then on another one), where you use two different aliases for the
table?
In theory, it's better to support both table names and alias names.
But in calcite, the alias name of subquery or table would not be lost in
the sql conversion phase and sql optimization phase.
So here we only support table names.

Best,
Jing Zhang


Francesco Guardiani  于2022年1月3日周一 18:38写道：

> Hi Jing,
>
> Thanks for the FLIP. I'm not very knowledgeable about the topic, but going
> through both the FLIP and the discussion here, I wonder, does it makes
> sense for a lookup join to use hash distribution whenever is possible by
> default?
>
> The point you're explaining here:
>
> > Many Lookup table sources introduce cache in order
> to reduce the RPC call, such as JDBC, CSV, HBase connectors.
> For those connectors, we could raise cache hit ratio by routing the same
> lookup keys to the same task instance
>
> Seems something we can infer automatically, rather than manually asking the
> user to add this hint to the query. Note that I'm not talking against the
> hint syntax, which might still make sense to be introduced, but I feel like
> this optimization makes sense in the general case when using the connectors
> you have quoted. Perhaps there is some downside I'm not aware of?
>
> Talking about the hint themselves, taking this example as reference:
>
> SELECT /*+ SHUFFLE_HASH('Orders', 'Customers') */ o.order_id, o.total,
> c.country, c.zip
> FROM Orders AS o
> JOIN Customers FOR SYSTEM_TIME AS OF o.proc_time AS c
> ON o.customer_id = c.id;
>
> Shouldn't the hint take the table alias as the "table name"? What If you do
> two lookup joins in cascade within the same query with the same table (once
> on a key, then on another one), where you use two different aliases for the
> table?
>
>
> On Fri, Dec 31, 2021 at 9:56 AM Jing Zhang  wrote:
>
> > Hi Lincoln,
> > Thanks for the feedback.
> >
> > > 1. For the hint name, +1 for WenLong's proposal.
> >
> > I've added add 'SHUFFLE_HASH' to other alternatives in FLIP. Let's
> waiting
> > for more voices here.
> >
> > > Regarding the `SKEW` hint, agree with you that it can be used widely,
> and
> > I
> > prefer to treat it as a metadata hint, a new category differs from a join
> > hint.
> > For your example:
> > ```
> > SELECT /*+ USE_HASH('Orders', 'Customers'), SKEW('Orders') */ o.order_id,
> > o.total, c.country, c.zip
> > FROM Orders AS o
> > JOIN Customers FOR SYSTEM_TIME AS OF o.proc_time AS c
> > ON o.customer_id = c.id;
> > ```
> > I would prefer another form:
> > ```
> > -- provide the skew info to let the engine choose the optimal plan
> > SELECT /*+ SKEW('Orders') */ o.order_id, ...
> >
> > -- or introduce a new hint for the join case, e.g.,
> > SELECT /*+ REPLICATED_SHUFFLE_HASH('Orders') */ o.order_id, ...
> > ```
> >
> > Maybe there is misunderstanding here.
> > I just use a syntax sugar here.
> >
> > SELECT /*+ USE_HASH('Orders', 'Customers'), SKEW('Orders') */ o.order_id,
> > 
> >
> > is just a syntax with
> >
> > SELECT /*+ USE_HASH('Orders', 'Customers') */ /*+SKEW('Orders') */
> > o.order_id,
> > 
> >
> > Although I list 'USE_HASH' and 'SKEW' hint in a query hint clause, it
> does
> > not mean they must appear together as a whole.
> > Based on calcite syntax doc [1], you could list more than one hint in
> > a /*+' hint [, hint ]* '*/ clause.
> >
> > Each hint has different function.
> > The'USE_HASH' hint suggests the optimizer use hash partitioner for Lookup
> > Join for table 'Orders' and table 'Customers' while the 'SKEW' hint tells
> > the optimizer the skew metadata about the table 'Orders'.
> >
> > Best,
> > Jing Zhang
> >
> > [1] https://calcite.apache.org/docs/reference.html#sql-hints
> >
> >
> >
> >
> > Jing Zhang  于2021年12月31日周五 16:39写道：
> >
> > > Hi Martijn,
> > > Thanks for the feedback.
> > >
> > > Glad to hear that we reached a consensus on the first and second point.
> > >
> > > About whether to use `use_hash` as a term, I think your concern makes
> > > sense.
> > > Although the hash 

Re: Re: [DISCUSS] Introduce Hash Lookup Join

[Francesco Guardiani]

Hi Jing,

Thanks for the FLIP. I'm not very knowledgeable about the topic, but going
through both the FLIP and the discussion here, I wonder, does it makes
sense for a lookup join to use hash distribution whenever is possible by
default?

The point you're explaining here:

> Many Lookup table sources introduce cache in order
to reduce the RPC call, such as JDBC, CSV, HBase connectors.
For those connectors, we could raise cache hit ratio by routing the same
lookup keys to the same task instance

Seems something we can infer automatically, rather than manually asking the
user to add this hint to the query. Note that I'm not talking against the
hint syntax, which might still make sense to be introduced, but I feel like
this optimization makes sense in the general case when using the connectors
you have quoted. Perhaps there is some downside I'm not aware of?

Talking about the hint themselves, taking this example as reference:

SELECT /*+ SHUFFLE_HASH('Orders', 'Customers') */ o.order_id, o.total,
c.country, c.zip
FROM Orders AS o
JOIN Customers FOR SYSTEM_TIME AS OF o.proc_time AS c
ON o.customer_id = c.id;

Shouldn't the hint take the table alias as the "table name"? What If you do
two lookup joins in cascade within the same query with the same table (once
on a key, then on another one), where you use two different aliases for the
table?


On Fri, Dec 31, 2021 at 9:56 AM Jing Zhang  wrote:

> Hi Lincoln,
> Thanks for the feedback.
>
> > 1. For the hint name, +1 for WenLong's proposal.
>
> I've added add 'SHUFFLE_HASH' to other alternatives in FLIP. Let's waiting
> for more voices here.
>
> > Regarding the `SKEW` hint, agree with you that it can be used widely, and
> I
> prefer to treat it as a metadata hint, a new category differs from a join
> hint.
> For your example:
> ```
> SELECT /*+ USE_HASH('Orders', 'Customers'), SKEW('Orders') */ o.order_id,
> o.total, c.country, c.zip
> FROM Orders AS o
> JOIN Customers FOR SYSTEM_TIME AS OF o.proc_time AS c
> ON o.customer_id = c.id;
> ```
> I would prefer another form:
> ```
> -- provide the skew info to let the engine choose the optimal plan
> SELECT /*+ SKEW('Orders') */ o.order_id, ...
>
> -- or introduce a new hint for the join case, e.g.,
> SELECT /*+ REPLICATED_SHUFFLE_HASH('Orders') */ o.order_id, ...
> ```
>
> Maybe there is misunderstanding here.
> I just use a syntax sugar here.
>
> SELECT /*+ USE_HASH('Orders', 'Customers'), SKEW('Orders') */ o.order_id,
> 
>
> is just a syntax with
>
> SELECT /*+ USE_HASH('Orders', 'Customers') */ /*+SKEW('Orders') */
> o.order_id,
> 
>
> Although I list 'USE_HASH' and 'SKEW' hint in a query hint clause, it does
> not mean they must appear together as a whole.
> Based on calcite syntax doc [1], you could list more than one hint in
> a /*+' hint [, hint ]* '*/ clause.
>
> Each hint has different function.
> The'USE_HASH' hint suggests the optimizer use hash partitioner for Lookup
> Join for table 'Orders' and table 'Customers' while the 'SKEW' hint tells
> the optimizer the skew metadata about the table 'Orders'.
>
> Best,
> Jing Zhang
>
> [1] https://calcite.apache.org/docs/reference.html#sql-hints
>
>
>
>
> Jing Zhang  于2021年12月31日周五 16:39写道：
>
> > Hi Martijn,
> > Thanks for the feedback.
> >
> > Glad to hear that we reached a consensus on the first and second point.
> >
> > About whether to use `use_hash` as a term, I think your concern makes
> > sense.
> > Although the hash lookup join is similar to Hash join in oracle that they
> > all require hash distribution on input, there exists a little difference
> > between them.
> > About this point, Lincoln and WenLong both prefer the term
> 'SHUFFLE_HASH',
> > WDYT?
> >
> > Best,
> > Jing Zhang
> >
> >
> > Lincoln Lee  于2021年12月30日周四 11:21写道：
> >
> >> Hi Jing,
> >> Thanks for your explanation!
> >>
> >> 1. For the hint name, +1 for WenLong's proposal. I think the `SHUFFLE`
> >> keyword is important in a classic distributed computing system,
> >> a hash-join usually means there's a shuffle stage(include shuffle
> >> hash-join, broadcast hash-join). Users only need to pass the `build`
> side
> >> table(usually the smaller one) into `SHUFFLE_HASH` join hint, more
> >> concisely than `USE_HASH(left_table, right_table)`. Please correct me if
> >> my
> >> understanding is wrong.
> >> Regarding the `SKEW` hint, agree with you that it can be used widely,
> and
> >> I
> >> prefer to treat it as a metadata hint, a new category differs from a
> join
> >> hint.
> >> For your example:
> >> ```
> >> SELECT /*+ USE_HASH('Orders', 'Customers'), SKEW('Orders') */
> o.order_id,
> >> o.total, c.country, c.zip
> >> FROM Orders AS o
> >> JOIN Customers FOR SYSTEM_TIME AS OF o.proc_time AS c
> >> ON o.customer_id = c.id;
> >> ```
> >> I would prefer another form:
> >> ```
> >> -- provide the skew info to let the engine choose the optimal plan
> >> SELECT /*+ SKEW('Orders') */ o.order_id, ...
> >>
> >> -- or introduce a new hint for the join case, e.g.,
> >> SELECT /*+ 

Re: Re: [DISCUSS] Introduce Hash Lookup Join

[Jing Zhang]

Hi Lincoln,
Thanks for the feedback.

> 1. For the hint name, +1 for WenLong's proposal.

I've added add 'SHUFFLE_HASH' to other alternatives in FLIP. Let's waiting
for more voices here.

> Regarding the `SKEW` hint, agree with you that it can be used widely, and
I
prefer to treat it as a metadata hint, a new category differs from a join
hint.
For your example:
```
SELECT /*+ USE_HASH('Orders', 'Customers'), SKEW('Orders') */ o.order_id,
o.total, c.country, c.zip
FROM Orders AS o
JOIN Customers FOR SYSTEM_TIME AS OF o.proc_time AS c
ON o.customer_id = c.id;
```
I would prefer another form:
```
-- provide the skew info to let the engine choose the optimal plan
SELECT /*+ SKEW('Orders') */ o.order_id, ...

-- or introduce a new hint for the join case, e.g.,
SELECT /*+ REPLICATED_SHUFFLE_HASH('Orders') */ o.order_id, ...
```

Maybe there is misunderstanding here.
I just use a syntax sugar here.

SELECT /*+ USE_HASH('Orders', 'Customers'), SKEW('Orders') */ o.order_id,


is just a syntax with

SELECT /*+ USE_HASH('Orders', 'Customers') */ /*+SKEW('Orders') */
o.order_id,


Although I list 'USE_HASH' and 'SKEW' hint in a query hint clause, it does
not mean they must appear together as a whole.
Based on calcite syntax doc [1], you could list more than one hint in
a /*+' hint [, hint ]* '*/ clause.

Each hint has different function.
The'USE_HASH' hint suggests the optimizer use hash partitioner for Lookup
Join for table 'Orders' and table 'Customers' while the 'SKEW' hint tells
the optimizer the skew metadata about the table 'Orders'.

Best,
Jing Zhang

[1] https://calcite.apache.org/docs/reference.html#sql-hints




Jing Zhang  于2021年12月31日周五 16:39写道：

> Hi Martijn,
> Thanks for the feedback.
>
> Glad to hear that we reached a consensus on the first and second point.
>
> About whether to use `use_hash` as a term, I think your concern makes
> sense.
> Although the hash lookup join is similar to Hash join in oracle that they
> all require hash distribution on input, there exists a little difference
> between them.
> About this point, Lincoln and WenLong both prefer the term 'SHUFFLE_HASH',
> WDYT?
>
> Best,
> Jing Zhang
>
>
> Lincoln Lee  于2021年12月30日周四 11:21写道：
>
>> Hi Jing,
>> Thanks for your explanation!
>>
>> 1. For the hint name, +1 for WenLong's proposal. I think the `SHUFFLE`
>> keyword is important in a classic distributed computing system,
>> a hash-join usually means there's a shuffle stage(include shuffle
>> hash-join, broadcast hash-join). Users only need to pass the `build` side
>> table(usually the smaller one) into `SHUFFLE_HASH` join hint, more
>> concisely than `USE_HASH(left_table, right_table)`. Please correct me if
>> my
>> understanding is wrong.
>> Regarding the `SKEW` hint, agree with you that it can be used widely, and
>> I
>> prefer to treat it as a metadata hint, a new category differs from a join
>> hint.
>> For your example:
>> ```
>> SELECT /*+ USE_HASH('Orders', 'Customers'), SKEW('Orders') */ o.order_id,
>> o.total, c.country, c.zip
>> FROM Orders AS o
>> JOIN Customers FOR SYSTEM_TIME AS OF o.proc_time AS c
>> ON o.customer_id = c.id;
>> ```
>> I would prefer another form:
>> ```
>> -- provide the skew info to let the engine choose the optimal plan
>> SELECT /*+ SKEW('Orders') */ o.order_id, ...
>>
>> -- or introduce a new hint for the join case, e.g.,
>> SELECT /*+ REPLICATED_SHUFFLE_HASH('Orders') */ o.order_id, ...
>> ```
>>
>> 2. Agree with Martin adding the feature to 1.16, we need time to complete
>> the change in calcite and also the upgrading work.
>>
>> 3. I misunderstood the 'Other Alternatives' part as the 'Rejected' ones in
>> the FLIP doc. And my point is avoiding the hacky way with our best effort.
>> The potential issues for calcite's hint propagation， e.g., join hints
>> correctly propagate into proper join scope include subquery or views which
>> may have various sql operators, so we should check all kinds of operators
>> for the correct propagation. Hope this may help. And also cc @Shuo Cheng
>> may
>> offer more help.
>>
>>
>> Best,
>> Lincoln Lee
>>
>>
>> Martijn Visser  于2021年12月29日周三 22:21写道：
>>
>> > Hi Jing,
>> >
>> > Thanks for explaining this in more detail and also to others
>> > participating.
>> >
>> > > I think using query hints in this case is more natural for users,
>> WDYT?
>> >
>> > Yes, I agree. As long as we properly explain in our documentation that
>> we
>> > support both Query Hints and Table Hints, what's the difference between
>> > them and how to use them, I think our users can understand this
>> perfectly.
>> >
>> > > I admit upgrading from Calcite 1.26 to 1.30 would be a big change.
>> > However we could not always avoid upgrade for the following reason
>> >
>> > We have to upgrade Calcite. We actually considered putting that in the
>> > Flink 1.15 scope but ultimately had to drop it, but I definitely think
>> this
>> > needs to be done for 1.16. It's not only because of new features that
>> are
>> > depending on Calcite 

Re: Re: [DISCUSS] Introduce Hash Lookup Join

[Jing Zhang]

Hi Martijn,
Thanks for the feedback.

Glad to hear that we reached a consensus on the first and second point.

About whether to use `use_hash` as a term, I think your concern makes sense.
Although the hash lookup join is similar to Hash join in oracle that they
all require hash distribution on input, there exists a little difference
between them.
About this point, Lincoln and WenLong both prefer the term 'SHUFFLE_HASH',
WDYT?

Best,
Jing Zhang


Lincoln Lee  于2021年12月30日周四 11:21写道：

> Hi Jing,
> Thanks for your explanation!
>
> 1. For the hint name, +1 for WenLong's proposal. I think the `SHUFFLE`
> keyword is important in a classic distributed computing system,
> a hash-join usually means there's a shuffle stage(include shuffle
> hash-join, broadcast hash-join). Users only need to pass the `build` side
> table(usually the smaller one) into `SHUFFLE_HASH` join hint, more
> concisely than `USE_HASH(left_table, right_table)`. Please correct me if my
> understanding is wrong.
> Regarding the `SKEW` hint, agree with you that it can be used widely, and I
> prefer to treat it as a metadata hint, a new category differs from a join
> hint.
> For your example:
> ```
> SELECT /*+ USE_HASH('Orders', 'Customers'), SKEW('Orders') */ o.order_id,
> o.total, c.country, c.zip
> FROM Orders AS o
> JOIN Customers FOR SYSTEM_TIME AS OF o.proc_time AS c
> ON o.customer_id = c.id;
> ```
> I would prefer another form:
> ```
> -- provide the skew info to let the engine choose the optimal plan
> SELECT /*+ SKEW('Orders') */ o.order_id, ...
>
> -- or introduce a new hint for the join case, e.g.,
> SELECT /*+ REPLICATED_SHUFFLE_HASH('Orders') */ o.order_id, ...
> ```
>
> 2. Agree with Martin adding the feature to 1.16, we need time to complete
> the change in calcite and also the upgrading work.
>
> 3. I misunderstood the 'Other Alternatives' part as the 'Rejected' ones in
> the FLIP doc. And my point is avoiding the hacky way with our best effort.
> The potential issues for calcite's hint propagation， e.g., join hints
> correctly propagate into proper join scope include subquery or views which
> may have various sql operators, so we should check all kinds of operators
> for the correct propagation. Hope this may help. And also cc @Shuo Cheng
> may
> offer more help.
>
>
> Best,
> Lincoln Lee
>
>
> Martijn Visser  于2021年12月29日周三 22:21写道：
>
> > Hi Jing,
> >
> > Thanks for explaining this in more detail and also to others
> > participating.
> >
> > > I think using query hints in this case is more natural for users, WDYT?
> >
> > Yes, I agree. As long as we properly explain in our documentation that we
> > support both Query Hints and Table Hints, what's the difference between
> > them and how to use them, I think our users can understand this
> perfectly.
> >
> > > I admit upgrading from Calcite 1.26 to 1.30 would be a big change.
> > However we could not always avoid upgrade for the following reason
> >
> > We have to upgrade Calcite. We actually considered putting that in the
> > Flink 1.15 scope but ultimately had to drop it, but I definitely think
> this
> > needs to be done for 1.16. It's not only because of new features that are
> > depending on Calcite upgrades, but also because newer versions have
> > resolved bugs that also hurt our users. That's why we also already have
> > tickets for upgrading to Calcite 1.27 [1] and 1.28 [2].
> >
> > With regards to using `use_hash` as a term, I think the most important
> part
> > is that if we re-use a term like Oracle is using, is that the behaviour
> and
> > outcome should be the same/comparable to the one from (in this case)
> > Oracle. If their behaviour and outcome are not the same or comparable, I
> > would probably introduce our own term to avoid that users get confused.
> >
> > Best regards,
> >
> > Martijn
> >
> > [1] https://issues.apache.org/jira/browse/FLINK-20873
> > [2] https://issues.apache.org/jira/browse/FLINK-21239
> >
> > On Wed, 29 Dec 2021 at 14:18, Jing Zhang  wrote:
> >
> > > Hi Jian gang,
> > > Thanks for the feedback.
> > >
> > > > When it comes to hive, how do you load partial data instead of the
> > >whole data? Any change related with hive?
> > >
> > > The question is same as Yuan mentioned before.
> > > I prefer to drive another FLIP on this topic to further discussion
> > > individually because this point involves many extension on API.
> > > Here I would like to share the implementation in our internal version
> > > firstly, it maybe very different with the final solution which merged
> to
> > > community.
> > > The core idea is push the partitioner information down to the lookup
> > table
> > > source.
> > > Hive connector need also upgrades. When loading data into caches, each
> > task
> > > could only store records which look keys are sent to current task.
> > >
> > > > How to define the cache configuration? For example, the size and the
> > ttl.
> > >
> > > I'm afraid there is no a unify caching configuration and cache
> > > implementation of 

Re: Re: [DISCUSS] Introduce Hash Lookup Join

[Lincoln Lee]

Hi Jing,
Thanks for your explanation!

1. For the hint name, +1 for WenLong's proposal. I think the `SHUFFLE`
keyword is important in a classic distributed computing system,
a hash-join usually means there's a shuffle stage(include shuffle
hash-join, broadcast hash-join). Users only need to pass the `build` side
table(usually the smaller one) into `SHUFFLE_HASH` join hint, more
concisely than `USE_HASH(left_table, right_table)`. Please correct me if my
understanding is wrong.
Regarding the `SKEW` hint, agree with you that it can be used widely, and I
prefer to treat it as a metadata hint, a new category differs from a join
hint.
For your example:
```
SELECT /*+ USE_HASH('Orders', 'Customers'), SKEW('Orders') */ o.order_id,
o.total, c.country, c.zip
FROM Orders AS o
JOIN Customers FOR SYSTEM_TIME AS OF o.proc_time AS c
ON o.customer_id = c.id;
```
I would prefer another form:
```
-- provide the skew info to let the engine choose the optimal plan
SELECT /*+ SKEW('Orders') */ o.order_id, ...

-- or introduce a new hint for the join case, e.g.,
SELECT /*+ REPLICATED_SHUFFLE_HASH('Orders') */ o.order_id, ...
```

2. Agree with Martin adding the feature to 1.16, we need time to complete
the change in calcite and also the upgrading work.

3. I misunderstood the 'Other Alternatives' part as the 'Rejected' ones in
the FLIP doc. And my point is avoiding the hacky way with our best effort.
The potential issues for calcite's hint propagation， e.g., join hints
correctly propagate into proper join scope include subquery or views which
may have various sql operators, so we should check all kinds of operators
for the correct propagation. Hope this may help. And also cc @Shuo Cheng may
offer more help.


Best,
Lincoln Lee


Martijn Visser  于2021年12月29日周三 22:21写道：

> Hi Jing,
>
> Thanks for explaining this in more detail and also to others
> participating.
>
> > I think using query hints in this case is more natural for users, WDYT?
>
> Yes, I agree. As long as we properly explain in our documentation that we
> support both Query Hints and Table Hints, what's the difference between
> them and how to use them, I think our users can understand this perfectly.
>
> > I admit upgrading from Calcite 1.26 to 1.30 would be a big change.
> However we could not always avoid upgrade for the following reason
>
> We have to upgrade Calcite. We actually considered putting that in the
> Flink 1.15 scope but ultimately had to drop it, but I definitely think this
> needs to be done for 1.16. It's not only because of new features that are
> depending on Calcite upgrades, but also because newer versions have
> resolved bugs that also hurt our users. That's why we also already have
> tickets for upgrading to Calcite 1.27 [1] and 1.28 [2].
>
> With regards to using `use_hash` as a term, I think the most important part
> is that if we re-use a term like Oracle is using, is that the behaviour and
> outcome should be the same/comparable to the one from (in this case)
> Oracle. If their behaviour and outcome are not the same or comparable, I
> would probably introduce our own term to avoid that users get confused.
>
> Best regards,
>
> Martijn
>
> [1] https://issues.apache.org/jira/browse/FLINK-20873
> [2] https://issues.apache.org/jira/browse/FLINK-21239
>
> On Wed, 29 Dec 2021 at 14:18, Jing Zhang  wrote:
>
> > Hi Jian gang,
> > Thanks for the feedback.
> >
> > > When it comes to hive, how do you load partial data instead of the
> >whole data? Any change related with hive?
> >
> > The question is same as Yuan mentioned before.
> > I prefer to drive another FLIP on this topic to further discussion
> > individually because this point involves many extension on API.
> > Here I would like to share the implementation in our internal version
> > firstly, it maybe very different with the final solution which merged to
> > community.
> > The core idea is push the partitioner information down to the lookup
> table
> > source.
> > Hive connector need also upgrades. When loading data into caches, each
> task
> > could only store records which look keys are sent to current task.
> >
> > > How to define the cache configuration? For example, the size and the
> ttl.
> >
> > I'm afraid there is no a unify caching configuration and cache
> > implementation of different connectors yet.
> > You could find cache size and ttl config of JDBC in doc [1], HBase in doc
> > [2]
> >
> > >  Will this feature add another shuffle phase compared with the default
> >behavior? In what situations will user choose this feature?
> >
> > Yes, if user specify hash hint in query, optimizer would prefer to choose
> > Hash Lookup Join, which would add a Hash Shuffle.
> > If lookup table source has cache inside (for example HBase/Jdbc) and the
> > benefit of increasing cache hit ratio is bigger than add an extra shuffle
> > cost, the user could use Hash Lookup Join.
> >
> > >  For the keys, the default implementation will be ok. But I wonder
> > whether we can support more 

Re: Re: [DISCUSS] Introduce Hash Lookup Join

[Martijn Visser]

Hi Jing,

Thanks for explaining this in more detail and also to others
participating.

> I think using query hints in this case is more natural for users, WDYT?

Yes, I agree. As long as we properly explain in our documentation that we
support both Query Hints and Table Hints, what's the difference between
them and how to use them, I think our users can understand this perfectly.

> I admit upgrading from Calcite 1.26 to 1.30 would be a big change.
However we could not always avoid upgrade for the following reason

We have to upgrade Calcite. We actually considered putting that in the
Flink 1.15 scope but ultimately had to drop it, but I definitely think this
needs to be done for 1.16. It's not only because of new features that are
depending on Calcite upgrades, but also because newer versions have
resolved bugs that also hurt our users. That's why we also already have
tickets for upgrading to Calcite 1.27 [1] and 1.28 [2].

With regards to using `use_hash` as a term, I think the most important part
is that if we re-use a term like Oracle is using, is that the behaviour and
outcome should be the same/comparable to the one from (in this case)
Oracle. If their behaviour and outcome are not the same or comparable, I
would probably introduce our own term to avoid that users get confused.

Best regards,

Martijn

[1] https://issues.apache.org/jira/browse/FLINK-20873
[2] https://issues.apache.org/jira/browse/FLINK-21239

On Wed, 29 Dec 2021 at 14:18, Jing Zhang  wrote:

> Hi Jian gang,
> Thanks for the feedback.
>
> > When it comes to hive, how do you load partial data instead of the
>whole data? Any change related with hive?
>
> The question is same as Yuan mentioned before.
> I prefer to drive another FLIP on this topic to further discussion
> individually because this point involves many extension on API.
> Here I would like to share the implementation in our internal version
> firstly, it maybe very different with the final solution which merged to
> community.
> The core idea is push the partitioner information down to the lookup table
> source.
> Hive connector need also upgrades. When loading data into caches, each task
> could only store records which look keys are sent to current task.
>
> > How to define the cache configuration? For example, the size and the ttl.
>
> I'm afraid there is no a unify caching configuration and cache
> implementation of different connectors yet.
> You could find cache size and ttl config of JDBC in doc [1], HBase in doc
> [2]
>
> >  Will this feature add another shuffle phase compared with the default
>behavior? In what situations will user choose this feature?
>
> Yes, if user specify hash hint in query, optimizer would prefer to choose
> Hash Lookup Join, which would add a Hash Shuffle.
> If lookup table source has cache inside (for example HBase/Jdbc) and the
> benefit of increasing cache hit ratio is bigger than add an extra shuffle
> cost, the user could use Hash Lookup Join.
>
> >  For the keys, the default implementation will be ok. But I wonder
> whether we can support more flexible strategies.
>
> The question is same as Yuan mentioned before.
>
> I'm afraid there is no plan to support flexible strategies yet because the
> feature involves many things, for example:
> 1. sql syntax
> 2. user defined partitioner API
> 3. RelDistribution type extension and Flink RelDistribution extension
> 4. FlinkExpandConversionRule
> 5. Exchange execNode extension
> 6. 
> It needs well designed and more discussion. If this is a strong
> requirement, we would drive another discussion on this point individually.
> In this FLIP, I would first support hash shuffle. WDYT?
>
> Best,
> Jing Zhang
>
> [1]
>
> https://nightlies.apache.org/flink/flink-docs-master/docs/connectors/table/jdbc/#connector-options
> [2]
>
> https://nightlies.apache.org/flink/flink-docs-master/docs/connectors/table/hbase/#connector-options
>
> Jing Zhang  于2021年12月29日周三 20:37写道：
>
> > Hi Wenlong,
> > Thanks for the feedback.
> > I've checked similar syntax in other systems, they are all different from
> > each other. It seems to be without consensus.
> > As mentioned in FLIP-204, oracle uses a query hint, the hint name is
> > 'use_hash' [1].
> > Spark also uses a query hint, its name is 'SHUFFLE_HASH' [2].
> > SQL Server uses keyword 'HASH' instead of query hint [3].
> > Note, the purposes of hash shuffle in [1][2][3] are a little different
> > from the purpose of FLIP-204, we just discuss syntax here.
> >
> > I've added this part to FLIP waiting for further discussion.
> >
> > Best,
> > Jing Zhang
> >
> > [1]
> > https://docs.oracle.com/cd/B12037_01/server.101/b10752/hintsref.htm#5683
> > [2]
> > https://spark.apache.org/docs/3.0.0/sql-ref-syntax-qry-select-hints.html
> > [3]
> >
> https://docs.microsoft.com/en-us/sql/t-sql/queries/hints-transact-sql-join?view=sql-server-ver15
> >
> >
> > wenlong.lwl  于2021年12月29日周三 17:18写道：
> >
> >> Hi, Jing, thanks for driving the discussion.
> >>
> >> Have you made 

Re: Re: [DISCUSS] Introduce Hash Lookup Join

[Jing Zhang]

Hi Jian gang,
Thanks for the feedback.

> When it comes to hive, how do you load partial data instead of the
   whole data? Any change related with hive?

The question is same as Yuan mentioned before.
I prefer to drive another FLIP on this topic to further discussion
individually because this point involves many extension on API.
Here I would like to share the implementation in our internal version
firstly, it maybe very different with the final solution which merged to
community.
The core idea is push the partitioner information down to the lookup table
source.
Hive connector need also upgrades. When loading data into caches, each task
could only store records which look keys are sent to current task.

> How to define the cache configuration? For example, the size and the ttl.

I'm afraid there is no a unify caching configuration and cache
implementation of different connectors yet.
You could find cache size and ttl config of JDBC in doc [1], HBase in doc
[2]

>  Will this feature add another shuffle phase compared with the default
   behavior? In what situations will user choose this feature?

Yes, if user specify hash hint in query, optimizer would prefer to choose
Hash Lookup Join, which would add a Hash Shuffle.
If lookup table source has cache inside (for example HBase/Jdbc) and the
benefit of increasing cache hit ratio is bigger than add an extra shuffle
cost, the user could use Hash Lookup Join.

>  For the keys, the default implementation will be ok. But I wonder
whether we can support more flexible strategies.

The question is same as Yuan mentioned before.

I'm afraid there is no plan to support flexible strategies yet because the
feature involves many things, for example:
1. sql syntax
2. user defined partitioner API
3. RelDistribution type extension and Flink RelDistribution extension
4. FlinkExpandConversionRule
5. Exchange execNode extension
6. 
It needs well designed and more discussion. If this is a strong
requirement, we would drive another discussion on this point individually.
In this FLIP, I would first support hash shuffle. WDYT?

Best,
Jing Zhang

[1]
https://nightlies.apache.org/flink/flink-docs-master/docs/connectors/table/jdbc/#connector-options
[2]
https://nightlies.apache.org/flink/flink-docs-master/docs/connectors/table/hbase/#connector-options

Jing Zhang  于2021年12月29日周三 20:37写道：

> Hi Wenlong,
> Thanks for the feedback.
> I've checked similar syntax in other systems, they are all different from
> each other. It seems to be without consensus.
> As mentioned in FLIP-204, oracle uses a query hint, the hint name is
> 'use_hash' [1].
> Spark also uses a query hint, its name is 'SHUFFLE_HASH' [2].
> SQL Server uses keyword 'HASH' instead of query hint [3].
> Note, the purposes of hash shuffle in [1][2][3] are a little different
> from the purpose of FLIP-204, we just discuss syntax here.
>
> I've added this part to FLIP waiting for further discussion.
>
> Best,
> Jing Zhang
>
> [1]
> https://docs.oracle.com/cd/B12037_01/server.101/b10752/hintsref.htm#5683
> [2]
> https://spark.apache.org/docs/3.0.0/sql-ref-syntax-qry-select-hints.html
> [3]
> https://docs.microsoft.com/en-us/sql/t-sql/queries/hints-transact-sql-join?view=sql-server-ver15
>
>
> wenlong.lwl  于2021年12月29日周三 17:18写道：
>
>> Hi, Jing, thanks for driving the discussion.
>>
>> Have you made some investigation on the syntax of join hint?
>> Why do you choose USE_HASH from oracle instead of the style of spark
>> SHUFFLE_HASH, they are quite different.
>> People in the big data world may be more familiar with spark/hive, if we
>> need to choose one, personally, I prefer the style of spark.
>>
>>
>> Best,
>> Wenlong
>>
>> On Wed, 29 Dec 2021 at 16:48, zst...@163.com  wrote:
>>
>> >
>> >
>> >
>> > Hi Jing,
>> > Thanks for your detail reply.
>> > 1) In the last suggestion, hash by primary key is not use for raising
>> the
>> > cache hit, but handling with skew of left source. Now that you have
>> 'skew'
>> > hint and other discussion about it, I'm looking forward to it.
>> > 2) I mean to support user defined partitioner function. We have a case
>> > that joining a datalake source with special way of partition, and have
>> > implemented not elegantly in our internal version. As you said, it needs
>> > more design.
>> > 3) I thing so-called 'HashPartitionedCache' is usefull, otherwise
>> loading
>> > all data such as hive lookup table source is almost not available in big
>> > data.
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> > Best regards,
>> > Yuan
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> > 在 2021-12-29 14:52:11，"Jing Zhang"  写道：
>> > >Hi, Lincoln
>> > >Thanks a lot for the feedback.
>> > >
>> > >>  Regarding the hint name ‘USE_HASH’, could we consider more
>> candidates?
>> > >Things are a little different from RDBMS in the distributed world, and
>> we
>> > >also aim to solve the data skew problem, so all these incoming hints
>> names
>> > >should be considered together.
>> > >
>> > >About skew problem, I would discuss this 

Re: Re: [DISCUSS] Introduce Hash Lookup Join

[Jing Zhang]

 Hi Wenlong,
Thanks for the feedback.
I've checked similar syntax in other systems, they are all different from
each other. It seems to be without consensus.
As mentioned in FLIP-204, oracle uses a query hint, the hint name is
'use_hash' [1].
Spark also uses a query hint, its name is 'SHUFFLE_HASH' [2].
SQL Server uses keyword 'HASH' instead of query hint [3].
Note, the purposes of hash shuffle in [1][2][3] are a little different from
the purpose of FLIP-204, we just discuss syntax here.

I've added this part to FLIP waiting for further discussion.

Best,
Jing Zhang

[1] https://docs.oracle.com/cd/B12037_01/server.101/b10752/hintsref.htm#5683
[2] https://spark.apache.org/docs/3.0.0/sql-ref-syntax-qry-select-hints.html
[3]
https://docs.microsoft.com/en-us/sql/t-sql/queries/hints-transact-sql-join?view=sql-server-ver15


wenlong.lwl  于2021年12月29日周三 17:18写道：

> Hi, Jing, thanks for driving the discussion.
>
> Have you made some investigation on the syntax of join hint?
> Why do you choose USE_HASH from oracle instead of the style of spark
> SHUFFLE_HASH, they are quite different.
> People in the big data world may be more familiar with spark/hive, if we
> need to choose one, personally, I prefer the style of spark.
>
>
> Best,
> Wenlong
>
> On Wed, 29 Dec 2021 at 16:48, zst...@163.com  wrote:
>
> >
> >
> >
> > Hi Jing,
> > Thanks for your detail reply.
> > 1) In the last suggestion, hash by primary key is not use for raising the
> > cache hit, but handling with skew of left source. Now that you have
> 'skew'
> > hint and other discussion about it, I'm looking forward to it.
> > 2) I mean to support user defined partitioner function. We have a case
> > that joining a datalake source with special way of partition, and have
> > implemented not elegantly in our internal version. As you said, it needs
> > more design.
> > 3) I thing so-called 'HashPartitionedCache' is usefull, otherwise loading
> > all data such as hive lookup table source is almost not available in big
> > data.
> >
> >
> >
> >
> >
> >
> >
> > Best regards,
> > Yuan
> >
> >
> >
> >
> >
> >
> >
> >
> > 在 2021-12-29 14:52:11，"Jing Zhang"  写道：
> > >Hi, Lincoln
> > >Thanks a lot for the feedback.
> > >
> > >>  Regarding the hint name ‘USE_HASH’, could we consider more
> candidates?
> > >Things are a little different from RDBMS in the distributed world, and
> we
> > >also aim to solve the data skew problem, so all these incoming hints
> names
> > >should be considered together.
> > >
> > >About skew problem, I would discuss this in next FLIP individually. I
> > would
> > >like to share hint proposal for skew here.
> > >I want to introduce 'skew' hint which is a query hint, similar with skew
> > >hint in spark [1] and MaxCompute[2].
> > >The 'skew' hint could only contain the name of the table with skew.
> > >Besides, skew hint could accept table name and column names.
> > >In addition, skew hint could accept table name, column names and skew
> > >values.
> > >For example:
> > >
> > >SELECT /*+ USE_HASH('Orders', 'Customers'), SKEW('Orders') */
> o.order_id,
> > >o.total, c.country, c.zip
> > >FROM Orders AS o
> > >JOIN Customers FOR SYSTEM_TIME AS OF o.proc_time AS c
> > >ON o.customer_id = c.id;
> > >
> > >The 'skew' hint is not only used for look up join here, but also could
> be
> > >used for other types of join later, for example, batch hash join or
> > >streaming regular join.
> > >Go back to better name problem for hash look up join. Since the 'skew'
> > hint
> > >is a separate hint, so 'use_hash' is still an alternative.
> > >WDYT?
> > >I don't have a good idea about the better hint name yet. I would like to
> > >heard more suggestions about hint names.
> > >
> > >>  As you mentioned in the flip, this solution depends on future changes
> > to
> > >calcite (and also upgrading calcite would be another possible big
> change:
> > >at least calicite-1.30 vs 1.26, are we preparing to accept this big
> > >change?).
> > >
> > >Indeed, solution 1 depends on calcite upgrade.
> > >I admit upgrade from Calcite 1.26 to 1.30 would be a big change. I still
> > >remember what we have suffered from last upgrade to Calcite 1.26.
> > >However we could not always avoid upgrade for the following reason:
> > >1. Other features also depends on the Calcite upgrade. For example,
> > Session
> > >Window and Count Window.
> > >2. If we always avoid Calcite upgrade, there would be more gap with the
> > >latest version. One day, if upgrading becomes a thing which has to be
> > done,
> > >the pain is more.
> > >
> > >WDYT?
> > >
> > >>  Is there another possible way to minimize the change in calcite?
> > >
> > >Do you check the 'Other Alternatives' part in the FLIP-204? It gives
> > >another solution which does not depend on calcite upgrade and do not
> need
> > >to worry about the hint would be missed in the propagation.
> > >This is also what we have done in the internal version.
> > >The core idea is propagating 'use_hash' hint to TableScan with matched
> > >table 

Re: Re: [DISCUSS] Introduce Hash Lookup Join

[刘建刚]

Thank you for the proposal, Jing. I like the idea to partition data by some
key to improve the cache hit. I have some questions:

   1. When it comes to hive, how do you load partial data instead of the
   whole data? Any change related with hive?
   2. How to define the cache configuration? For example, the size and the
   ttl.
   3. Will this feature add another shuffle phase compared with the default
   behavior? In what situations will user choose this feature?
   4. For the keys, the default implementation will be ok. But I wonder
   whether we can support more flexible strategies.


wenlong.lwl  于2021年12月29日周三 17:18写道：

> Hi, Jing, thanks for driving the discussion.
>
> Have you made some investigation on the syntax of join hint?
> Why do you choose USE_HASH from oracle instead of the style of spark
> SHUFFLE_HASH, they are quite different.
> People in the big data world may be more familiar with spark/hive, if we
> need to choose one, personally, I prefer the style of spark.
>
>
> Best,
> Wenlong
>
> On Wed, 29 Dec 2021 at 16:48, zst...@163.com  wrote:
>
> >
> >
> >
> > Hi Jing,
> > Thanks for your detail reply.
> > 1) In the last suggestion, hash by primary key is not use for raising the
> > cache hit, but handling with skew of left source. Now that you have
> 'skew'
> > hint and other discussion about it, I'm looking forward to it.
> > 2) I mean to support user defined partitioner function. We have a case
> > that joining a datalake source with special way of partition, and have
> > implemented not elegantly in our internal version. As you said, it needs
> > more design.
> > 3) I thing so-called 'HashPartitionedCache' is usefull, otherwise loading
> > all data such as hive lookup table source is almost not available in big
> > data.
> >
> >
> >
> >
> >
> >
> >
> > Best regards,
> > Yuan
> >
> >
> >
> >
> >
> >
> >
> >
> > 在 2021-12-29 14:52:11，"Jing Zhang"  写道：
> > >Hi, Lincoln
> > >Thanks a lot for the feedback.
> > >
> > >>  Regarding the hint name ‘USE_HASH’, could we consider more
> candidates?
> > >Things are a little different from RDBMS in the distributed world, and
> we
> > >also aim to solve the data skew problem, so all these incoming hints
> names
> > >should be considered together.
> > >
> > >About skew problem, I would discuss this in next FLIP individually. I
> > would
> > >like to share hint proposal for skew here.
> > >I want to introduce 'skew' hint which is a query hint, similar with skew
> > >hint in spark [1] and MaxCompute[2].
> > >The 'skew' hint could only contain the name of the table with skew.
> > >Besides, skew hint could accept table name and column names.
> > >In addition, skew hint could accept table name, column names and skew
> > >values.
> > >For example:
> > >
> > >SELECT /*+ USE_HASH('Orders', 'Customers'), SKEW('Orders') */
> o.order_id,
> > >o.total, c.country, c.zip
> > >FROM Orders AS o
> > >JOIN Customers FOR SYSTEM_TIME AS OF o.proc_time AS c
> > >ON o.customer_id = c.id;
> > >
> > >The 'skew' hint is not only used for look up join here, but also could
> be
> > >used for other types of join later, for example, batch hash join or
> > >streaming regular join.
> > >Go back to better name problem for hash look up join. Since the 'skew'
> > hint
> > >is a separate hint, so 'use_hash' is still an alternative.
> > >WDYT?
> > >I don't have a good idea about the better hint name yet. I would like to
> > >heard more suggestions about hint names.
> > >
> > >>  As you mentioned in the flip, this solution depends on future changes
> > to
> > >calcite (and also upgrading calcite would be another possible big
> change:
> > >at least calicite-1.30 vs 1.26, are we preparing to accept this big
> > >change?).
> > >
> > >Indeed, solution 1 depends on calcite upgrade.
> > >I admit upgrade from Calcite 1.26 to 1.30 would be a big change. I still
> > >remember what we have suffered from last upgrade to Calcite 1.26.
> > >However we could not always avoid upgrade for the following reason:
> > >1. Other features also depends on the Calcite upgrade. For example,
> > Session
> > >Window and Count Window.
> > >2. If we always avoid Calcite upgrade, there would be more gap with the
> > >latest version. One day, if upgrading becomes a thing which has to be
> > done,
> > >the pain is more.
> > >
> > >WDYT?
> > >
> > >>  Is there another possible way to minimize the change in calcite?
> > >
> > >Do you check the 'Other Alternatives' part in the FLIP-204? It gives
> > >another solution which does not depend on calcite upgrade and do not
> need
> > >to worry about the hint would be missed in the propagation.
> > >This is also what we have done in the internal version.
> > >The core idea is propagating 'use_hash' hint to TableScan with matched
> > >table names.  However, it is a little hacky.
> > >
> > >> As I know there're more limitations than `Correlate`.
> > >
> > >As mentioned before, in our external version, I choose the the 'Other
> > >Alternatives' part in the FLIP-204.
> > 

Re: Re: [DISCUSS] Introduce Hash Lookup Join

[wenlong.lwl]

Hi, Jing, thanks for driving the discussion.

Have you made some investigation on the syntax of join hint?
Why do you choose USE_HASH from oracle instead of the style of spark
SHUFFLE_HASH, they are quite different.
People in the big data world may be more familiar with spark/hive, if we
need to choose one, personally, I prefer the style of spark.


Best,
Wenlong

On Wed, 29 Dec 2021 at 16:48, zst...@163.com  wrote:

>
>
>
> Hi Jing,
> Thanks for your detail reply.
> 1) In the last suggestion, hash by primary key is not use for raising the
> cache hit, but handling with skew of left source. Now that you have 'skew'
> hint and other discussion about it, I'm looking forward to it.
> 2) I mean to support user defined partitioner function. We have a case
> that joining a datalake source with special way of partition, and have
> implemented not elegantly in our internal version. As you said, it needs
> more design.
> 3) I thing so-called 'HashPartitionedCache' is usefull, otherwise loading
> all data such as hive lookup table source is almost not available in big
> data.
>
>
>
>
>
>
>
> Best regards,
> Yuan
>
>
>
>
>
>
>
>
> 在 2021-12-29 14:52:11，"Jing Zhang"  写道：
> >Hi, Lincoln
> >Thanks a lot for the feedback.
> >
> >>  Regarding the hint name ‘USE_HASH’, could we consider more candidates?
> >Things are a little different from RDBMS in the distributed world, and we
> >also aim to solve the data skew problem, so all these incoming hints names
> >should be considered together.
> >
> >About skew problem, I would discuss this in next FLIP individually. I
> would
> >like to share hint proposal for skew here.
> >I want to introduce 'skew' hint which is a query hint, similar with skew
> >hint in spark [1] and MaxCompute[2].
> >The 'skew' hint could only contain the name of the table with skew.
> >Besides, skew hint could accept table name and column names.
> >In addition, skew hint could accept table name, column names and skew
> >values.
> >For example:
> >
> >SELECT /*+ USE_HASH('Orders', 'Customers'), SKEW('Orders') */ o.order_id,
> >o.total, c.country, c.zip
> >FROM Orders AS o
> >JOIN Customers FOR SYSTEM_TIME AS OF o.proc_time AS c
> >ON o.customer_id = c.id;
> >
> >The 'skew' hint is not only used for look up join here, but also could be
> >used for other types of join later, for example, batch hash join or
> >streaming regular join.
> >Go back to better name problem for hash look up join. Since the 'skew'
> hint
> >is a separate hint, so 'use_hash' is still an alternative.
> >WDYT?
> >I don't have a good idea about the better hint name yet. I would like to
> >heard more suggestions about hint names.
> >
> >>  As you mentioned in the flip, this solution depends on future changes
> to
> >calcite (and also upgrading calcite would be another possible big change:
> >at least calicite-1.30 vs 1.26, are we preparing to accept this big
> >change?).
> >
> >Indeed, solution 1 depends on calcite upgrade.
> >I admit upgrade from Calcite 1.26 to 1.30 would be a big change. I still
> >remember what we have suffered from last upgrade to Calcite 1.26.
> >However we could not always avoid upgrade for the following reason:
> >1. Other features also depends on the Calcite upgrade. For example,
> Session
> >Window and Count Window.
> >2. If we always avoid Calcite upgrade, there would be more gap with the
> >latest version. One day, if upgrading becomes a thing which has to be
> done,
> >the pain is more.
> >
> >WDYT?
> >
> >>  Is there another possible way to minimize the change in calcite?
> >
> >Do you check the 'Other Alternatives' part in the FLIP-204? It gives
> >another solution which does not depend on calcite upgrade and do not need
> >to worry about the hint would be missed in the propagation.
> >This is also what we have done in the internal version.
> >The core idea is propagating 'use_hash' hint to TableScan with matched
> >table names.  However, it is a little hacky.
> >
> >> As I know there're more limitations than `Correlate`.
> >
> >As mentioned before, in our external version, I choose the the 'Other
> >Alternatives' part in the FLIP-204.
> >Although I do a POC in the solution 1 and lists all changes I found in the
> >FLIP, there may still be something I missed.
> >I'm very happy to hear that you point out there're more limitations except
> >for `Correlate`, would you please give more details on this part?
> >
> >Best,
> >Jing Zhang
> >
> >[1] https://docs.databricks.com/delta/join-performance/skew-join.html
> >[2]
> >
> https://help.aliyun.com/apsara/enterprise/v_3_13_0_20201215/odps/enterprise-ascm-user-guide/hotspot-tilt.html?spm=a2c4g.14484438.10001.669
> >
> >Jing Zhang  于2021年12月29日周三 14:40写道：
> >
> >> Hi Yuan and Lincoln,
> >> thanks a lot for the attention. I would answer the email one by one.
> >>
> >> To Yuan
> >> > How shall we deal with CDC data? If there is CDC data in the pipeline,
> >> IMHO, shuffle by join key will cause CDC data disorder. Will it be
> better
> >> to use primary key in this 

Re: [DISCUSS] Introduce Hash Lookup Join

[Jing Zhang]

Hi, Lincoln
Thanks a lot for the feedback.

>  Regarding the hint name ‘USE_HASH’, could we consider more candidates?
Things are a little different from RDBMS in the distributed world, and we
also aim to solve the data skew problem, so all these incoming hints names
should be considered together.

About skew problem, I would discuss this in next FLIP individually. I would
like to share hint proposal for skew here.
I want to introduce 'skew' hint which is a query hint, similar with skew
hint in spark [1] and MaxCompute[2].
The 'skew' hint could only contain the name of the table with skew.
Besides, skew hint could accept table name and column names.
In addition, skew hint could accept table name, column names and skew
values.
For example:

SELECT /*+ USE_HASH('Orders', 'Customers'), SKEW('Orders') */ o.order_id,
o.total, c.country, c.zip
FROM Orders AS o
JOIN Customers FOR SYSTEM_TIME AS OF o.proc_time AS c
ON o.customer_id = c.id;

The 'skew' hint is not only used for look up join here, but also could be
used for other types of join later, for example, batch hash join or
streaming regular join.
Go back to better name problem for hash look up join. Since the 'skew' hint
is a separate hint, so 'use_hash' is still an alternative.
WDYT?
I don't have a good idea about the better hint name yet. I would like to
heard more suggestions about hint names.

>  As you mentioned in the flip, this solution depends on future changes to
calcite (and also upgrading calcite would be another possible big change:
at least calicite-1.30 vs 1.26, are we preparing to accept this big
change?).

Indeed, solution 1 depends on calcite upgrade.
I admit upgrade from Calcite 1.26 to 1.30 would be a big change. I still
remember what we have suffered from last upgrade to Calcite 1.26.
However we could not always avoid upgrade for the following reason:
1. Other features also depends on the Calcite upgrade. For example, Session
Window and Count Window.
2. If we always avoid Calcite upgrade, there would be more gap with the
latest version. One day, if upgrading becomes a thing which has to be done,
the pain is more.

WDYT?

>  Is there another possible way to minimize the change in calcite?

Do you check the 'Other Alternatives' part in the FLIP-204? It gives
another solution which does not depend on calcite upgrade and do not need
to worry about the hint would be missed in the propagation.
This is also what we have done in the internal version.
The core idea is propagating 'use_hash' hint to TableScan with matched
table names.  However, it is a little hacky.

> As I know there're more limitations than `Correlate`.

As mentioned before, in our external version, I choose the the 'Other
Alternatives' part in the FLIP-204.
Although I do a POC in the solution 1 and lists all changes I found in the
FLIP, there may still be something I missed.
I'm very happy to hear that you point out there're more limitations except
for `Correlate`, would you please give more details on this part?

Best,
Jing Zhang

[1] https://docs.databricks.com/delta/join-performance/skew-join.html
[2]
https://help.aliyun.com/apsara/enterprise/v_3_13_0_20201215/odps/enterprise-ascm-user-guide/hotspot-tilt.html?spm=a2c4g.14484438.10001.669

Jing Zhang  于2021年12月29日周三 14:40写道：

> Hi Yuan and Lincoln,
> thanks a lot for the attention. I would answer the email one by one.
>
> To Yuan
> > How shall we deal with CDC data? If there is CDC data in the pipeline,
> IMHO, shuffle by join key will cause CDC data disorder. Will it be better
> to use primary key in this case?
>
> Good question.
> The problem could not only exists in CDC data source, but also exists when
> the input stream is not insert-only stream (for example, the result of
> unbounded aggregate or regular join).
> I think use hash by primary key is not a good choise. It could not raise
> the cache hit because cache key is look up key instead of primary key of
> input.
>
> To avoid wrong result, hash lookup Join requires that the input stream
> should be insert_only stream or its upsert keys contains lookup keys.
>
> I've added this limitation to FLIP, thanks a lot for reminding.
>
> > If the shuffle keys can be customized  when users have the knowledge
> about distribution of data?
>
> I'm not sure I understand your question.
>
> Do you mean to support user defined partitioner function on keys just like
> flink DataStream sql?
> If yes, I'm afraid there is no plan to support this feature yet because
> the feature involves many things, for example:
> 1. sql syntax
> 2. user defined partitioner API
> 3. RelDistribution type extension and Flink RelDistribution extension
> 4. FlinkExpandConversionRule
> 5. Exchange execNode extension
> 6. 
> It needs well designed and more discussion. If this is a strong
> requirement, we would drive another discussion on this point individually.
> In this FLIP, I would first support hash shuffle. WDYT?
>
> Or do you mean support hash by other keys instead of lookup key?
> If yes, would 

Re: [DISCUSS] Introduce Hash Lookup Join

[Jing Zhang]

Hi Yuan and Lincoln,
thanks a lot for the attention. I would answer the email one by one.

To Yuan
> How shall we deal with CDC data? If there is CDC data in the pipeline,
IMHO, shuffle by join key will cause CDC data disorder. Will it be better
to use primary key in this case?

Good question.
The problem could not only exists in CDC data source, but also exists when
the input stream is not insert-only stream (for example, the result of
unbounded aggregate or regular join).
I think use hash by primary key is not a good choise. It could not raise
the cache hit because cache key is look up key instead of primary key of
input.

To avoid wrong result, hash lookup Join requires that the input stream
should be insert_only stream or its upsert keys contains lookup keys.

I've added this limitation to FLIP, thanks a lot for reminding.

> If the shuffle keys can be customized  when users have the knowledge
about distribution of data?

I'm not sure I understand your question.

Do you mean to support user defined partitioner function on keys just like
flink DataStream sql?
If yes, I'm afraid there is no plan to support this feature yet because the
feature involves many things, for example:
1. sql syntax
2. user defined partitioner API
3. RelDistribution type extension and Flink RelDistribution extension
4. FlinkExpandConversionRule
5. Exchange execNode extension
6. 
It needs well designed and more discussion. If this is a strong
requirement, we would drive another discussion on this point individually.
In this FLIP, I would first support hash shuffle. WDYT?

Or do you mean support hash by other keys instead of lookup key?
If yes, would you please tell me a specific user case?
We need to fetch the record from external storage of dimension table by
look up key, so those dimension table source uses look up keys as cache
key.
We could only increase  the cache ratio by shuffle lookup keys.
I need more use cases to understand this requirement.

> Some connectors such as hive, caches all data in LookupFunction. How to
decrease the valid cache data size if data can be shuffled?

Very good idea.
There are two types of cache.
For Key-Value storage, such as Redis/HBase, the lookup table source stores
the visited lookup keys and it's record into cache lazily.
For other storage without keys, such as hive, each task loads all data into
cache eagerly in the initialize phase.
After introduce hash partitioner, for key-value storages, there is no need
to change; for hive, each task could only load part of cache instead of
load all cache.

We have implemented this optimization in our internal version.
The core idea is push the partitioner information down to the lookup table
source. When loading data into caches, each task could only store those
records which look keys are sent to current task.
We called this 'HashPartitionedCache'.

I have added this point into the Lookup Join requirements list in the
motivation of the FLIP, but I would not do this point in this FLIP right
now.
If this is a strong requirement, we need drive another discussion on this
topic individually because this point involves many extension on API.

Best,
Jing Zhang


Lincoln Lee  于2021年12月29日周三 10:01写道：

> Hi Jing,
> Thanks for bringing up this discussion!  Agree that this join hints
> should benefit both bounded and unbounded cases as Martin mentioned.
> I also agree that implementing the query hint is the right way for a more
> general purpose since the dynamic table options has a limited scope.
>Some points I'd like to share are:
> 1. Regarding the hint name ‘USE_HASH’, could we consider more candidates?
> Things are a little different from RDBMS in the distributed world, and we
> also aim to solve the data skew problem, so all these incoming hints names
> should be considered together.
> 2. As you mentioned in the flip, this solution depends on future changes to
> calcite (and also upgrading calcite would be another possible big change:
> at least calicite-1.30 vs 1.26, are we preparing to accept this big
> change?). Is there another possible way to minimize the change in calcite?
> As I know there're more limitations than `Correlate`.
>
> Best,
> Lincoln Lee
>
>
> Jing Zhang  于2021年12月28日周二 23:04写道：
>
> > Hi Martijn,
> > Thanks a lot for your attention.
> > I'm sorry I didn't explain the motivation clearly. I would like to
> explain
> > it in detail, and then give response on your questions.
> > A lookup join is typically used to enrich a table with data that is
> queried
> > from an external system. Many Lookup table sources introduce cache in
> order
> > to reduce the RPC call, such as JDBC, CSV, HBase connectors.
> > For those connectors, we could raise cache hit ratio by routing the same
> > lookup keys to the same task instance. This is the purpose of
> >
> >
> https://cwiki.apache.org/confluence/display/FLINK/FLIP-204%3A+Introduce+Hash+Lookup+Join
> > .
> > Other cases might benefit from Hash distribution, such as batch hash join
> > as 

Re: [DISCUSS] Introduce Hash Lookup Join

[Lincoln Lee]

Hi Jing,
Thanks for bringing up this discussion!  Agree that this join hints
should benefit both bounded and unbounded cases as Martin mentioned.
I also agree that implementing the query hint is the right way for a more
general purpose since the dynamic table options has a limited scope.
   Some points I'd like to share are:
1. Regarding the hint name ‘USE_HASH’, could we consider more candidates?
Things are a little different from RDBMS in the distributed world, and we
also aim to solve the data skew problem, so all these incoming hints names
should be considered together.
2. As you mentioned in the flip, this solution depends on future changes to
calcite (and also upgrading calcite would be another possible big change:
at least calicite-1.30 vs 1.26, are we preparing to accept this big
change?). Is there another possible way to minimize the change in calcite?
As I know there're more limitations than `Correlate`.

Best,
Lincoln Lee


Jing Zhang  于2021年12月28日周二 23:04写道：

> Hi Martijn,
> Thanks a lot for your attention.
> I'm sorry I didn't explain the motivation clearly. I would like to explain
> it in detail, and then give response on your questions.
> A lookup join is typically used to enrich a table with data that is queried
> from an external system. Many Lookup table sources introduce cache in order
> to reduce the RPC call, such as JDBC, CSV, HBase connectors.
> For those connectors, we could raise cache hit ratio by routing the same
> lookup keys to the same task instance. This is the purpose of
>
> https://cwiki.apache.org/confluence/display/FLINK/FLIP-204%3A+Introduce+Hash+Lookup+Join
> .
> Other cases might benefit from Hash distribution, such as batch hash join
> as you mentioned. It is a cool idea, however it is not the purpose of this
> FLIP, we could discuss this in FLINK-20670
> .
>
> > - When I was reading about this topic [1] I was wondering if this feature
> would be more beneficial for bounded use cases and not so much for
> unbounded use cases. What do you think?
>
> As mentioned before, the purpose of Hash Lookup Join is to increase the
> cache hit ratio which is different from Oracle Hash Join. However we could
> use the similar hint syntax.
>
> > - If I look at the current documentation for SQL Hints in Flink [2], I
> notice that all of the hints there are located at the end of the SQL
> statement. In the FLIP, the use_hash is defined directly after the 'SELECT'
> keyword. Can we somehow make this consistent for the user? Or should the
> user be able to specify hints anywhere in its SQL statement?
>
> Calcite supports hints in two locations [3]:
> Query Hint: right after the SELECT keyword;
> Table Hint: right after the referenced table name.
> Now Flink has supported dynamic table options based on the Hint framework
> of Calcite which is mentioned in doc[2].
> Besides, query hints are also important, it could give a hint for
> optimizers to choose a better plan. Almost all popular databases and
> big-data engines support sql query hints, such as oracle, hive, spark and
> so on.
> I think using query hints in this case is more natural for users, WDYT?
>
> I have updated the motivation part in the FLIP,
> Thanks for the feedback!
>
> [1] https://logicalread.com/oracle-11g-hash-joins-mc02/#.V5Wm4_mnoUI
> [2]
>
> https://nightlies.apache.org/flink/flink-docs-stable/docs/dev/table/sql/queries/hints/
> [3] https://calcite.apache.org/docs/reference.html#sql-hints
>
> Best,
> Jing Zhang
>
> Martijn Visser  于2021年12月28日周二 22:02写道：
>
> > Hi Jing,
> >
> > Thanks a lot for the explanation and the FLIP. I definitely learned
> > something when reading more about `use_hash`. My interpretation would be
> > that the primary benefit of a hash lookup join would be improved
> > performance by allowing the user to explicitly optimise the planner.
> >
> > I have a couple of questions:
> >
> > - When I was reading about this topic [1] I was wondering if this feature
> > would be more beneficial for bounded use cases and not so much for
> > unbounded use cases. What do you think?
> > - If I look at the current documentation for SQL Hints in Flink [2], I
> > notice that all of the hints there are located at the end of the SQL
> > statement. In the FLIP, the use_hash is defined directly after the
> 'SELECT'
> > keyword. Can we somehow make this consistent for the user? Or should the
> > user be able to specify hints anywhere in its SQL statement?
> >
> > Best regards,
> >
> > Martijn
> >
> > [1] https://logicalread.com/oracle-11g-hash-joins-mc02/#.V5Wm4_mnoUI
> > [2]
> >
> >
> https://nightlies.apache.org/flink/flink-docs-stable/docs/dev/table/sql/queries/hints/
> >
> >
> > On Tue, 28 Dec 2021 at 08:17, Jing Zhang  wrote:
> >
> > > Hi everyone,
> > > Look up join
> > > <
> > >
> >
> https://nightlies.apache.org/flink/flink-docs-master/docs/dev/table/sql/queries/joins/#lookup-join
> > > >[1]
> > > is
> > > commonly used feature in Flink SQL. We have 

Re: [DISCUSS] Introduce Hash Lookup Join

[zst...@163.com]

Hi Jing,


Thanks very much for your FLIP. I have some points:


- How shall we deal with CDC data? If there is CDC data in the pipeline, IMHO, 
shuffle by join key will cause CDC data disorder. Will it be better to use 
primary key in this case?


- If the shuffle keys can be customized  when users have the knowledge about 
distribution of data?


- Some connectors such as hive, caches all data in LookupFunction. How to 
decrease the valid cache data size if data can be shuffled?


Best regards,


Yuan
On 12/28/2021 15:11，Jing Zhang wrote：
Hi everyone,
Look up join
[1]
is
commonly used feature in Flink SQL. We have received many optimization
requirements on look up join. For example:
1. Enforces left side of lookup join do a hash partitioner to raise cache
hint ratio
2. Solves the data skew problem after introduces hash lookup join
3. Enables mini-batch optimization to reduce RPC call

Next we will solve these problems one by one. Firstly,  we would focus on
point 1, and continue to discuss point 2 and point 3 later.

There are many similar requirements from user mail list and JIRA about hash
Lookup Join, for example:
1. FLINK-23687  -
Introduce partitioned lookup join to enforce input of LookupJoin to hash
shuffle by lookup keys
2. FLINK-25396  -
lookupjoin source table for pre-partitioning
3. FLINK-25262  -
Support to send data to lookup table for KeyGroupStreamPartitioner way for
SQL.

In this FLIP, I would like to start a discussion about Hash Lookup Join.
The core idea is introducing a 'USE_HASH' hint in query.  This syntax is
directly user-oriented and therefore requires careful design.
There are two ways about how to propagate this hint to LookupJoin in
optimizer. We need further discussion to do final decide. Anyway, the
difference between the two solution is only about the internal
implementation and has no impact on the user.

For more detail on the proposal:
https://cwiki.apache.org/confluence/display/FLINK/FLIP-204%3A+Introduce+Hash+Lookup+Join


Looking forward to your feedback, thanks.

Best,
Jing Zhang

[1]
https://nightlies.apache.org/flink/flink-docs-master/docs/dev/table/sql/queries/joins/#lookup-join

Re: [DISCUSS] Introduce Hash Lookup Join

[Jing Zhang]

Hi Martijn,
Thanks a lot for your attention.
I'm sorry I didn't explain the motivation clearly. I would like to explain
it in detail, and then give response on your questions.
A lookup join is typically used to enrich a table with data that is queried
from an external system. Many Lookup table sources introduce cache in order
to reduce the RPC call, such as JDBC, CSV, HBase connectors.
For those connectors, we could raise cache hit ratio by routing the same
lookup keys to the same task instance. This is the purpose of
https://cwiki.apache.org/confluence/display/FLINK/FLIP-204%3A+Introduce+Hash+Lookup+Join
.
Other cases might benefit from Hash distribution, such as batch hash join
as you mentioned. It is a cool idea, however it is not the purpose of this
FLIP, we could discuss this in FLINK-20670
.

> - When I was reading about this topic [1] I was wondering if this feature
would be more beneficial for bounded use cases and not so much for
unbounded use cases. What do you think?

As mentioned before, the purpose of Hash Lookup Join is to increase the
cache hit ratio which is different from Oracle Hash Join. However we could
use the similar hint syntax.

> - If I look at the current documentation for SQL Hints in Flink [2], I
notice that all of the hints there are located at the end of the SQL
statement. In the FLIP, the use_hash is defined directly after the 'SELECT'
keyword. Can we somehow make this consistent for the user? Or should the
user be able to specify hints anywhere in its SQL statement?

Calcite supports hints in two locations [3]:
Query Hint: right after the SELECT keyword;
Table Hint: right after the referenced table name.
Now Flink has supported dynamic table options based on the Hint framework
of Calcite which is mentioned in doc[2].
Besides, query hints are also important, it could give a hint for
optimizers to choose a better plan. Almost all popular databases and
big-data engines support sql query hints, such as oracle, hive, spark and
so on.
I think using query hints in this case is more natural for users, WDYT?

I have updated the motivation part in the FLIP,
Thanks for the feedback!

[1] https://logicalread.com/oracle-11g-hash-joins-mc02/#.V5Wm4_mnoUI
[2]
https://nightlies.apache.org/flink/flink-docs-stable/docs/dev/table/sql/queries/hints/
[3] https://calcite.apache.org/docs/reference.html#sql-hints

Best,
Jing Zhang

Martijn Visser  于2021年12月28日周二 22:02写道：

> Hi Jing,
>
> Thanks a lot for the explanation and the FLIP. I definitely learned
> something when reading more about `use_hash`. My interpretation would be
> that the primary benefit of a hash lookup join would be improved
> performance by allowing the user to explicitly optimise the planner.
>
> I have a couple of questions:
>
> - When I was reading about this topic [1] I was wondering if this feature
> would be more beneficial for bounded use cases and not so much for
> unbounded use cases. What do you think?
> - If I look at the current documentation for SQL Hints in Flink [2], I
> notice that all of the hints there are located at the end of the SQL
> statement. In the FLIP, the use_hash is defined directly after the 'SELECT'
> keyword. Can we somehow make this consistent for the user? Or should the
> user be able to specify hints anywhere in its SQL statement?
>
> Best regards,
>
> Martijn
>
> [1] https://logicalread.com/oracle-11g-hash-joins-mc02/#.V5Wm4_mnoUI
> [2]
>
> https://nightlies.apache.org/flink/flink-docs-stable/docs/dev/table/sql/queries/hints/
>
>
> On Tue, 28 Dec 2021 at 08:17, Jing Zhang  wrote:
>
> > Hi everyone,
> > Look up join
> > <
> >
> https://nightlies.apache.org/flink/flink-docs-master/docs/dev/table/sql/queries/joins/#lookup-join
> > >[1]
> > is
> > commonly used feature in Flink SQL. We have received many optimization
> > requirements on look up join. For example:
> > 1. Enforces left side of lookup join do a hash partitioner to raise cache
> > hint ratio
> > 2. Solves the data skew problem after introduces hash lookup join
> > 3. Enables mini-batch optimization to reduce RPC call
> >
> > Next we will solve these problems one by one. Firstly,  we would focus on
> > point 1, and continue to discuss point 2 and point 3 later.
> >
> > There are many similar requirements from user mail list and JIRA about
> hash
> > Lookup Join, for example:
> > 1. FLINK-23687  -
> > Introduce partitioned lookup join to enforce input of LookupJoin to hash
> > shuffle by lookup keys
> > 2. FLINK-25396  -
> > lookupjoin source table for pre-partitioning
> > 3. FLINK-25262  -
> > Support to send data to lookup table for KeyGroupStreamPartitioner way
> for
> > SQL.
> >
> > In this FLIP, I would like to start a discussion about Hash Lookup Join.
> > The core idea is introducing a 'USE_HASH' hint in query.  This syntax is
> 

Re: [DISCUSS] Introduce Hash Lookup Join

[Martijn Visser]

Hi Jing,

Thanks a lot for the explanation and the FLIP. I definitely learned
something when reading more about `use_hash`. My interpretation would be
that the primary benefit of a hash lookup join would be improved
performance by allowing the user to explicitly optimise the planner.

I have a couple of questions:

- When I was reading about this topic [1] I was wondering if this feature
would be more beneficial for bounded use cases and not so much for
unbounded use cases. What do you think?
- If I look at the current documentation for SQL Hints in Flink [2], I
notice that all of the hints there are located at the end of the SQL
statement. In the FLIP, the use_hash is defined directly after the 'SELECT'
keyword. Can we somehow make this consistent for the user? Or should the
user be able to specify hints anywhere in its SQL statement?

Best regards,

Martijn

[1] https://logicalread.com/oracle-11g-hash-joins-mc02/#.V5Wm4_mnoUI
[2]
https://nightlies.apache.org/flink/flink-docs-stable/docs/dev/table/sql/queries/hints/


On Tue, 28 Dec 2021 at 08:17, Jing Zhang  wrote:

> Hi everyone,
> Look up join
> <
> https://nightlies.apache.org/flink/flink-docs-master/docs/dev/table/sql/queries/joins/#lookup-join
> >[1]
> is
> commonly used feature in Flink SQL. We have received many optimization
> requirements on look up join. For example:
> 1. Enforces left side of lookup join do a hash partitioner to raise cache
> hint ratio
> 2. Solves the data skew problem after introduces hash lookup join
> 3. Enables mini-batch optimization to reduce RPC call
>
> Next we will solve these problems one by one. Firstly,  we would focus on
> point 1, and continue to discuss point 2 and point 3 later.
>
> There are many similar requirements from user mail list and JIRA about hash
> Lookup Join, for example:
> 1. FLINK-23687  -
> Introduce partitioned lookup join to enforce input of LookupJoin to hash
> shuffle by lookup keys
> 2. FLINK-25396  -
> lookupjoin source table for pre-partitioning
> 3. FLINK-25262  -
> Support to send data to lookup table for KeyGroupStreamPartitioner way for
> SQL.
>
> In this FLIP, I would like to start a discussion about Hash Lookup Join.
> The core idea is introducing a 'USE_HASH' hint in query.  This syntax is
> directly user-oriented and therefore requires careful design.
> There are two ways about how to propagate this hint to LookupJoin in
> optimizer. We need further discussion to do final decide. Anyway, the
> difference between the two solution is only about the internal
> implementation and has no impact on the user.
>
> For more detail on the proposal:
>
> https://cwiki.apache.org/confluence/display/FLINK/FLIP-204%3A+Introduce+Hash+Lookup+Join
>
>
> Looking forward to your feedback, thanks.
>
> Best,
> Jing Zhang
>
> [1]
>
> https://nightlies.apache.org/flink/flink-docs-master/docs/dev/table/sql/queries/joins/#lookup-join
>