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 <https://docs.oracle.com/cd/B12037_01/server.101/b10752/hintsref.htm#5683> 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 <https://impala.apache.org/docs/build/html/topics/impala_hints.html> 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 <jingsongl...@gmail.com> 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 <lincoln.8...@gmail.com> > 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 <beyond1...@gmail.com> 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 <beyond1...@gmail.com> 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 <france...@ververica.com> 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 <beyond1...@gmail.com> > > > 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 <beyond1...@gmail.com> 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 <lincoln.8...@gmail.com> 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 <mart...@ververica.com> 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 < > beyond1...@gmail.com> > > > >> > 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 <beyond1...@gmail.com> 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 <wenlong88....@gmail.com> 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 < > > > 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" < > beyond1...@gmail.com> > > > >> 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 <beyond1...@gmail.com> 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 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 <lincoln.8...@gmail.com> > 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 <beyond1...@gmail.com> 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 > > > >> > >> > > >> > >>> > < > https://issues.apache.org/jira/browse/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 <mart...@ververica.com> > > > 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 < > > > >> > >> > > beyond1...@gmail.com> > > > >> > >> > > >> > >>> 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 < > > > >> > >> > > >> > https://issues.apache.org/jira/browse/FLINK-23687> > > > >> > >> > > >> > >>> - > > > >> > >> > > >> > >>> > > > Introduce partitioned lookup join to enforce > > > >> input of > > > >> > >> > > >> LookupJoin > > > >> > >> > > >> > to > > > >> > >> > > >> > >>> > hash > > > >> > >> > > >> > >>> > > > shuffle by lookup keys > > > >> > >> > > >> > >>> > > > 2. FLINK-25396 < > > > >> > >> > > >> > https://issues.apache.org/jira/browse/FLINK-25396> > > > >> > >> > > >> > >>> - > > > >> > >> > > >> > >>> > > > lookupjoin source table for pre-partitioning > > > >> > >> > > >> > >>> > > > 3. FLINK-25262 < > > > >> > >> > > >> > https://issues.apache.org/jira/browse/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 > > > >> > >> > > >> > >>> > > > > > > >> > >> > > >> > >>> > > > > > >> > >> > > >> > >>> > > > > >> > >> > > >> > >>> > > > >> > >> > > >> > >> > > > >> > >> > > >> > > > > >> > >> > > >> > > > >> > >> > > > > > > >> > >> > > > > > >> > >> > > > > >> > >> > > > >> > > > > > >> > > > > >> > > > >> > > > > >
