Hi, Feng Thanks for driving this FLIP, Time travel is very useful for Flink integrate with data lake system. I have one question why the implementation of TimeTravel is delegated to Catalog? Assuming that we use Flink to query Hudi table with the time travel syntax, but we don't use the HudiCatalog, instead, we register the hudi table to InMemoryCatalog, can we support time travel for Hudi table in this case? In contrast, I think time travel should bind to connector instead of Catalog, so the rejected alternative should be considered.
Best, Ron yuxia <luoyu...@alumni.sjtu.edu.cn> 于2023年5月30日周二 09:40写道： > Hi, Feng. > Notice this FLIP only support batch mode for time travel. Would it also > make sense to support stream mode to a read a snapshot of the table as a > bounded stream? > > Best regards, > Yuxia > > ----- 原始邮件 ----- > 发件人: "Benchao Li" <libenc...@apache.org> > 收件人: "dev" <dev@flink.apache.org> > 发送时间: 星期一, 2023年 5 月 29日 下午 6:04:53 > 主题: Re: [DISCUSS] FLIP-308: Support Time Travel In Batch Mode > > # Can Calcite support this syntax ` VERSION AS OF` ? > > This also depends on whether this is defined in standard or any known > databases that have implemented this. If not, it would be hard to push it > to Calcite. > > # getTable(ObjectPath object, long timestamp) > > Then we again come to the problem of "casting between timestamp and > numeric", which has been disabled in FLINK-21978[1]. If you're gonna use > this, then we need to clarify that problem first. > > [1] https://issues.apache.org/jira/browse/FLINK-21978 > > > Feng Jin <jinfeng1...@gmail.com> 于2023年5月29日周一 15:57写道： > > > hi, thanks for your reply. > > > > @Benchao > > > did you consider the pushdown abilities compatible > > > > In the current design, the implementation of TimeTravel is delegated to > > Catalog. We have added a function called getTable(ObjectPath tablePath, > > long timestamp) to obtain the corresponding CatalogBaseTable at a > specific > > time. Therefore, I think it will not have any impact on the original > > pushdown abilities. > > > > > > > I see there is a rejected design for adding SupportsTimeTravel, but > I > > didn't see the alternative in the FLIP doc > > > > Sorry, the document description is not very clear. Regarding whether to > > support SupportTimeTravel, I have discussed it with yuxia. Since we have > > already passed the corresponding time in getTable(ObjectPath, long > > timestamp) of Catalog, SupportTimeTravel may not be necessary. > > > > In getTable(ObjectPath object, long timestamp), we can obtain the schema > of > > the corresponding time point and put the SNAPSHOT that needs to be > consumed > > into options. > > > > > > @Shammon > > > Could we support this in Flink too? > > > > I personally think it's possible, but limited by Calcite's syntax > > restrictions. I believe we should first support this syntax in Calcite. > > Currently, I think it may not be easy to support this syntax in Flink's > > parser. @Benchao, what do you think? Can Calcite support this syntax > > ` VERSION AS OF` ? > > > > > > Best, > > Feng. > > > > > > On Fri, May 26, 2023 at 2:55 PM Shammon FY <zjur...@gmail.com> wrote: > > > > > Thanks Feng, the feature of time travel sounds great! > > > > > > In addition to SYSTEM_TIME, lake houses such as paimon and iceberg > > support > > > snapshot or version. For example, users can query snapshot 1 for paimon > > by > > > the following statement > > > SELECT * FROM t VERSION AS OF 1 > > > > > > Could we support this in Flink too? > > > > > > Best, > > > Shammon FY > > > > > > On Fri, May 26, 2023 at 1:20 PM Benchao Li <libenc...@apache.org> > wrote: > > > > > > > Regarding the implementation, did you consider the pushdown abilities > > > > compatible, e.g., projection pushdown, filter pushdown, partition > > > pushdown. > > > > Since `Snapshot` is not handled much in existing rules, I have a > > concern > > > > about this. Of course, it depends on your implementation detail, what > > is > > > > important is that we'd better add some cross tests for these. > > > > > > > > Regarding the interface exposed to Connector, I see there is a > rejected > > > > design for adding SupportsTimeTravel, but I didn't see the > alternative > > in > > > > the FLIP doc. IMO, this is an important thing we need to clarify > > because > > > we > > > > need to know whether the Connector supports this, and what > > > column/metadata > > > > corresponds to 'system_time'. > > > > > > > > Feng Jin <jinfeng1...@gmail.com> 于2023年5月25日周四 22:50写道： > > > > > > > > > Thanks for your reply > > > > > > > > > > @Timo @BenChao @yuxia > > > > > > > > > > Sorry for the mistake, Currently , calcite only supports `FOR > > > > SYSTEM_TIME > > > > > AS OF ` syntax. We can only support `FOR SYSTEM_TIME AS OF` . > I've > > > > > updated the syntax part of the FLIP. > > > > > > > > > > > > > > > @Timo > > > > > > > > > > > We will convert it to TIMESTAMP_LTZ? > > > > > > > > > > Yes, I think we need to convert TIMESTAMP to TIMESTAMP_LTZ and then > > > > convert > > > > > it into a long value. > > > > > > > > > > > How do we want to query the most recent version of a table > > > > > > > > > > I think we can use `AS OF CURRENT_TIMESTAMP` ，But it does cause > > > > > inconsistency with the real-time concept. > > > > > However, from my personal understanding, the scope of `AS OF > > > > > CURRENT_TIMESTAMP` is the table itself, not the table record. So, > I > > > > think > > > > > using CURRENT_TIMESTAMP should also be reasonable?. > > > > > Additionally, if no version is specified, the latest version should > > be > > > > used > > > > > by default. > > > > > > > > > > > > > > > > > > > > Best, > > > > > Feng > > > > > > > > > > > > > > > On Thu, May 25, 2023 at 7:47 PM yuxia <luoyu...@alumni.sjtu.edu.cn > > > > > > wrote: > > > > > > > > > > > Thanks Feng for bringing this up. It'll be great to introduce > time > > > > travel > > > > > > to Flink to have a better integration with external data soruces. > > > > > > > > > > > > I also share same concern about the syntax. > > > > > > I see in the part of `Whether to support other syntax > > > implementations` > > > > in > > > > > > this FLIP, seems the syntax in Calcite should be `FOR SYSTEM_TIME > > AS > > > > OF`, > > > > > > right? > > > > > > But the the syntax part in this FLIP, it seems to be `AS OF > > > TIMESTAMP` > > > > > > instead of `FOR SYSTEM_TIME AS OF`. Is it just a mistake or by > > > design? > > > > > > > > > > > > > > > > > > Best regards, > > > > > > Yuxia > > > > > > > > > > > > ----- 原始邮件 ----- > > > > > > 发件人: "Benchao Li" <libenc...@apache.org> > > > > > > 收件人: "dev" <dev@flink.apache.org> > > > > > > 发送时间: 星期四, 2023年 5 月 25日 下午 7:27:17 > > > > > > 主题: Re: [DISCUSS] FLIP-308: Support Time Travel In Batch Mode > > > > > > > > > > > > Thanks Feng, it's exciting to have this ability. > > > > > > > > > > > > Regarding the syntax section, are you proposing `AS OF` instead > of > > > `FOR > > > > > > SYSTEM AS OF` to do this? I know `FOR SYSTEM AS OF` is in the SQL > > > > > standard > > > > > > and has been supported in some database vendors such as SQL > Server. > > > > About > > > > > > `AS OF`, is it in the standard or any database vendor supports > > this, > > > if > > > > > > yes, I think it's worth to add this support to Calcite, and I > would > > > > give > > > > > a > > > > > > hand in Calcite side. Otherwise, I think we'd better to use `FOR > > > SYSTEM > > > > > AS > > > > > > OF`. > > > > > > > > > > > > Timo Walther <twal...@apache.org> 于2023年5月25日周四 19:02写道： > > > > > > > > > > > > > Also: How do we want to query the most recent version of a > table? > > > > > > > > > > > > > > `AS OF CURRENT_TIMESTAMP` would be ideal, but according to the > > docs > > > > > both > > > > > > > the type is TIMESTAMP_LTZ and what is even more concerning is > the > > > it > > > > > > > actually is evalated row-based: > > > > > > > > > > > > > > > Returns the current SQL timestamp in the local time zone, > the > > > > return > > > > > > > type is TIMESTAMP_LTZ(3). It is evaluated for each record in > > > > streaming > > > > > > > mode. But in batch mode, it is evaluated once as the query > starts > > > and > > > > > > > uses the same result for every row. > > > > > > > > > > > > > > This could make it difficult to explain in a join scenario of > > > > multiple > > > > > > > snapshotted tables. > > > > > > > > > > > > > > Regards, > > > > > > > Timo > > > > > > > > > > > > > > > > > > > > > On 25.05.23 12:29, Timo Walther wrote: > > > > > > > > Hi Feng, > > > > > > > > > > > > > > > > thanks for proposing this FLIP. It makes a lot of sense to > > > finally > > > > > > > > support querying tables at a specific point in time or > > hopefully > > > > also > > > > > > > > ranges soon. Following time-versioned tables. > > > > > > > > > > > > > > > > Here is some feedback from my side: > > > > > > > > > > > > > > > > 1. Syntax > > > > > > > > > > > > > > > > Can you elaborate a bit on the Calcite restrictions? > > > > > > > > > > > > > > > > Does Calcite currently support `AS OF` syntax for this but > not > > > `FOR > > > > > > > > SYSTEM_TIME AS OF`? > > > > > > > > > > > > > > > > It would be great to support `AS OF` also for time-versioned > > > joins > > > > > and > > > > > > > > have a unified and short syntax. > > > > > > > > > > > > > > > > Once a fix is merged in Calcite for this, we can make this > > > > available > > > > > in > > > > > > > > Flink earlier by copying the corresponding classes until the > > next > > > > > > > > Calcite upgrade is performed. > > > > > > > > > > > > > > > > 2. Semantics > > > > > > > > > > > > > > > > How do we interpret the timestamp? In Flink we have 2 > timestamp > > > > types > > > > > > > > (TIMESTAMP and TIMESTAMP_LTZ). If users specify AS OF > TIMESTAMP > > > > > > > > '2023-04-27 00:00:00', in which timezone will the timestamp > be? > > > We > > > > > will > > > > > > > > convert it to TIMESTAMP_LTZ? > > > > > > > > > > > > > > > > We definely need to clarify this because the past has shown > > that > > > > > > > > daylight saving times make our lives hard. > > > > > > > > > > > > > > > > Thanks, > > > > > > > > Timo > > > > > > > > > > > > > > > > On 25.05.23 10:57, Feng Jin wrote: > > > > > > > >> Hi, everyone. > > > > > > > >> > > > > > > > >> I’d like to start a discussion about FLIP-308: Support Time > > > Travel > > > > > In > > > > > > > >> Batch > > > > > > > >> Mode [1] > > > > > > > >> > > > > > > > >> > > > > > > > >> Time travel is a SQL syntax used to query historical > versions > > of > > > > > data. > > > > > > > It > > > > > > > >> allows users to specify a point in time and retrieve the > data > > > and > > > > > > > >> schema of > > > > > > > >> a table as it appeared at that time. With time travel, users > > can > > > > > > easily > > > > > > > >> analyze and compare historical versions of data. > > > > > > > >> > > > > > > > >> > > > > > > > >> With the widespread use of data lake systems such as Paimon, > > > > > Iceberg, > > > > > > > and > > > > > > > >> Hudi, time travel can provide more convenience for users' > data > > > > > > analysis. > > > > > > > >> > > > > > > > >> > > > > > > > >> Looking forward to your opinions, any suggestions are > > welcomed. > > > > > > > >> > > > > > > > >> > > > > > > > >> > > > > > > > >> 1. > > > > > > > >> > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://cwiki.apache.org/confluence/display/FLINK/FLIP-308%3A+Support+Time+Travel+In+Batch+Mode > > > > > > > >> > > > > > > > >> > > > > > > > >> > > > > > > > >> Best. > > > > > > > >> > > > > > > > >> Feng > > > > > > > >> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > -- > > > > > > > > > > > > Best, > > > > > > Benchao Li > > > > > > > > > > > > > > > > > > > > > > > -- > > > > > > > > Best, > > > > Benchao Li > > > > > > > > > > > > -- > > Best, > Benchao Li >
