[DISCUSS] FLIP-84 Feedback Summary
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[DISCUSS] FLIP-84 Feedback Summary
 
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Re: [DISCUSS] FLIP-84 Feedback Summary
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Re: [DISCUSS] FLIP-84 Feedback Summary
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Re: [DISCUSS] FLIP-84 Feedback Summary
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Re: [DISCUSS] FLIP-84 Feedback Summary
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Re: [DISCUSS] FLIP-84 Feedback Summary
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Re: [DISCUSS] FLIP-84 Feedback Summary
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Re: [DISCUSS] FLIP-84 Feedback Summary
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Re: [DISCUSS] FLIP-84 Feedback Summary
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Re: [DISCUSS] FLIP-84 Feedback Summary
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Re: [DISCUSS] FLIP-84 Feedback Summary
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Re: [DISCUSS] FLIP-84 Feedback Summary
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Re: [DISCUSS] FLIP-84 Feedback Summary
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Re: [DISCUSS] FLIP-84 Feedback Summary
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Thank you Timo for the great summary! It covers (almost) all the topics.
Even though in the end we are not suggesting much changes to the current state of FLIP I think it is important to lay out all possible use cases so that we do not change the execution model every release. There is one additional thing we discussed. Could we change the result type of TableResult#collect to Iterator<Row>? Even though those interfaces do not differ much. I think Iterator better describes that the results might not be materialized on the client side, but can be retrieved on a per record basis. The contract of the Iterable#iterator is that it returns a new iterator each time, which effectively means we can iterate the results multiple times. Iterating the results is not possible when we don't retrieve all the results from the cluster at once. I think we should also use Iterator for TableEnvironment#executeMultilineSql(String statements): Iterator<TableResult>. Best, Dawid On 31/03/2020 19:27, Timo Walther wrote: > Hi Godfrey, > > Aljoscha, Dawid, Klou, and I had another discussion around FLIP-84. In > particular, we discussed how the current status of the FLIP and the > future requirements around multiline statements, async/sync, collect() > fit together. > > We also updated the FLIP-84 Feedback Summary document [1] with some > use cases. > > We believe that we found a good solution that also fits to what is in > the current FLIP. So no bigger changes necessary, which is great! > > Our findings were: > > 1. Async vs sync submission of Flink jobs: > > Having a blocking `execute()` in DataStream API was rather a mistake. > Instead all submissions should be async because this allows supporting > both modes if necessary. Thus, submitting all queries async sounds > good to us. If users want to run a job sync, they can use the > JobClient and wait for completion (or collect() in case of batch jobs). > > 2. Multi-statement execution: > > For the multi-statement execution, we don't see a contradication with > the async execution behavior. We imagine a method like: > > TableEnvironment#executeMultilineSql(String statements): > Iterable<TableResult> > > Where the `Iterator#next()` method would trigger the next statement > submission. This allows a caller to decide synchronously when to > submit statements async to the cluster. Thus, a service such as the > SQL Client can handle the result of each statement individually and > process statement by statement sequentially. > > 3. The role of TableResult and result retrieval in general > > `TableResult` is similar to `JobClient`. Instead of returning a > `CompletableFuture` of something, it is a concrete util class where > some methods have the behavior of completable future (e.g. collect(), > print()) and some are already completed (getTableSchema(), > getResultKind()). > > `StatementSet#execute()` returns a single `TableResult` because the > order is undefined in a set and all statements have the same schema. > Its `collect()` will return a row for each executed `INSERT INTO` in > the order of statement definition. > > For simple `SELECT * FROM ...`, the query execution might block until > `collect()` is called to pull buffered rows from the job (from > socket/REST API what ever we will use in the future). We can say that > a statement finished successfully, when the `collect#Iterator#hasNext` > has returned false. > > I hope this summarizes our discussion @Dawid/Aljoscha/Klou? > > It would be great if we can add these findings to the FLIP before we > start voting. > > One minor thing: some `execute()` methods still throw a checked > exception; can we remove that from the FLIP? Also the above mentioned > `Iterator#next()` would trigger an execution without throwing a > checked exception. > > Thanks, > Timo > > [1] > https://docs.google.com/document/d/1ueLjQWRPdLTFB_TReAyhseAX-1N3j4WYWD0F02Uau0E/edit# > > On 31.03.20 06:28, godfrey he wrote: >> Hi, Timo & Jark >> >> Thanks for your explanation. >> Agree with you that async execution should always be async, >> and sync execution scenario can be covered by async execution. >> It helps provide an unified entry point for batch and streaming. >> I think we can also use sync execution for some testing. >> So, I agree with you that we provide `executeSql` method and it's async >> method. >> If we want sync method in the future, we can add method named >> `executeSqlSync`. >> >> I think we've reached an agreement. I will update the document, and >> start >> voting process. >> >> Best, >> Godfrey >> >> >> Jark Wu <[hidden email]> 于2020年3月31日周二 上午12:46写道： >> >>> Hi, >>> >>> I didn't follow the full discussion. >>> But I share the same concern with Timo that streaming queries should >>> always >>> be async. >>> Otherwise, I can image it will cause a lot of confusion and problems if >>> users don't deeply keep the "sync" in mind (e.g. client hangs). >>> Besides, the streaming mode is still the majority use cases of Flink >>> and >>> Flink SQL. We should put the usability at a high priority. >>> >>> Best, >>> Jark >>> >>> >>> On Mon, 30 Mar 2020 at 23:27, Timo Walther <[hidden email]> wrote: >>> >>>> Hi Godfrey, >>>> >>>> maybe I wasn't expressing my biggest concern enough in my last mail. >>>> Even in a singleline and sync execution, I think that streaming >>>> queries >>>> should not block the execution. Otherwise it is not possible to call >>>> collect() or print() on them afterwards. >>>> >>>> "there are too many things need to discuss for multiline": >>>> >>>> True, I don't want to solve all of them right now. But what I know is >>>> that our newly introduced methods should fit into a multiline >>>> execution. >>>> There is no big difference of calling `executeSql(A), >>>> executeSql(B)` and >>>> processing a multiline file `A;\nB;`. >>>> >>>> I think the example that you mentioned can simply be undefined for >>>> now. >>>> Currently, no catalog is modifying data but just metadata. This is a >>>> separate discussion. >>>> >>>> "result of the second statement is indeterministic": >>>> >>>> Sure this is indeterministic. But this is the implementers fault >>>> and we >>>> cannot forbid such pipelines. >>>> >>>> How about we always execute streaming queries async? It would unblock >>>> executeSql() and multiline statements. >>>> >>>> Having a `executeSqlAsync()` is useful for batch. However, I don't >>>> want >>>> `sync/async` be the new batch/stream flag. The execution behavior >>>> should >>>> come from the query itself. >>>> >>>> Regards, >>>> Timo >>>> >>>> >>>> On 30.03.20 11:12, godfrey he wrote: >>>>> Hi Timo, >>>>> >>>>> Agree with you that streaming queries is our top priority, >>>>> but I think there are too many things need to discuss for multiline >>>>> statements: >>>>> e.g. >>>>> 1. what's the behaivor of DDL and DML mixing for async execution: >>>>> create table t1 xxx; >>>>> create table t2 xxx; >>>>> insert into t2 select * from t1 where xxx; >>>>> drop table t1; // t1 may be a MySQL table, the data will also be >>> deleted. >>>>> >>>>> t1 is dropped when "insert" job is running. >>>>> >>>>> 2. what's the behaivor of unified scenario for async execution: >>>>> (as you >>>>> mentioned) >>>>> INSERT INTO t1 SELECT * FROM s; >>>>> INSERT INTO t2 SELECT * FROM s JOIN t1 EMIT STREAM; >>>>> >>>>> The result of the second statement is indeterministic, because the >>> first >>>>> statement maybe is running. >>>>> I think we need to put a lot of effort to define the behavior of >>>> logically >>>>> related queries. >>>>> >>>>> In this FLIP, I suggest we only handle single statement, and we also >>>>> introduce an async execute method >>>>> which is more important and more often used for users. >>>>> >>>>> Dor the sync methods (like `TableEnvironment.executeSql` and >>>>> `StatementSet.execute`), >>>>> the result will be returned until the job is finished. The following >>>>> methods will be introduced in this FLIP: >>>>> >>>>> /** >>>>> * Asynchronously execute the given single statement >>>>> */ >>>>> TableEnvironment.executeSqlAsync(String statement): TableResult >>>>> >>>>> /** >>>>> * Asynchronously execute the dml statements as a batch >>>>> */ >>>>> StatementSet.executeAsync(): TableResult >>>>> >>>>> public interface TableResult { >>>>> /** >>>>> * return JobClient for DQL and DML in async mode, else return >>>>> Optional.empty >>>>> */ >>>>> Optional<JobClient> getJobClient(); >>>>> } >>>>> >>>>> what do you think? >>>>> >>>>> Best, >>>>> Godfrey >>>>> >>>>> Timo Walther <[hidden email]> 于2020年3月26日周四 下午9:15写道： >>>>> >>>>>> Hi Godfrey, >>>>>> >>>>>> executing streaming queries must be our top priority because this is >>>>>> what distinguishes Flink from competitors. If we change the >>>>>> execution >>>>>> behavior, we should think about the other cases as well to not break >>> the >>>>>> API a third time. >>>>>> >>>>>> I fear that just having an async execute method will not be enough >>>>>> because users should be able to mix streaming and batch queries in a >>>>>> unified scenario. >>>>>> >>>>>> If I remember it correctly, we had some discussions in the past >>>>>> about >>>>>> what decides about the execution mode of a query. Currently, we >>>>>> would >>>>>> like to let the query decide, not derive it from the sources. >>>>>> >>>>>> So I could image a multiline pipeline as: >>>>>> >>>>>> USE CATALOG 'mycat'; >>>>>> INSERT INTO t1 SELECT * FROM s; >>>>>> INSERT INTO t2 SELECT * FROM s JOIN t1 EMIT STREAM; >>>>>> >>>>>> For executeMultilineSql(): >>>>>> >>>>>> sync because regular SQL >>>>>> sync because regular Batch SQL >>>>>> async because Streaming SQL >>>>>> >>>>>> For executeAsyncMultilineSql(): >>>>>> >>>>>> async because everything should be async >>>>>> async because everything should be async >>>>>> async because everything should be async >>>>>> >>>>>> What we should not start for executeAsyncMultilineSql(): >>>>>> >>>>>> sync because DDL >>>>>> async because everything should be async >>>>>> async because everything should be async >>>>>> >>>>>> What are you thoughts here? >>>>>> >>>>>> Regards, >>>>>> Timo >>>>>> >>>>>> >>>>>> On 26.03.20 12:50, godfrey he wrote: >>>>>>> Hi Timo, >>>>>>> >>>>>>> I agree with you that streaming queries mostly need async >>>>>>> execution. >>>>>>> In fact, our original plan is only introducing sync methods in this >>>> FLIP, >>>>>>> and async methods (like "executeSqlAsync") will be introduced in >>>>>>> the >>>>>> future >>>>>>> which is mentioned in the appendix. >>>>>>> >>>>>>> Maybe the async methods also need to be considered in this FLIP. >>>>>>> >>>>>>> I think sync methods is also useful for streaming which can be used >>> to >>>>>> run >>>>>>> bounded source. >>>>>>> Maybe we should check whether all sources are bounded in sync >>> execution >>>>>>> mode. >>>>>>> >>>>>>>> Also, if we block for streaming queries, we could never support >>>>>>>> multiline files. Because the first INSERT INTO would block the >>> further >>>>>>>> execution. >>>>>>> agree with you, we need async method to submit multiline files, >>>>>>> and files should be limited that the DQL and DML should be >>>>>>> always in >>>> the >>>>>>> end for streaming. >>>>>>> >>>>>>> Best, >>>>>>> Godfrey >>>>>>> >>>>>>> Timo Walther <[hidden email]> 于2020年3月26日周四 下午4:29写道： >>>>>>> >>>>>>> >>>>>>>> Hi Godfrey, >>>>>>>> >>>>>>>> having control over the job after submission is a requirement that >>> was >>>>>>>> requested frequently (some examples are [1], [2]). Users would >>>>>>>> like >>> to >>>>>>>> get insights about the running or completed job. Including the >>> jobId, >>>>>>>> jobGraph etc., the JobClient summarizes these properties. >>>>>>>> >>>>>>>> It is good to have a discussion about synchronous/asynchronous >>>>>>>> submission now to have a complete execution picture. >>>>>>>> >>>>>>>> I thought we submit streaming queries mostly async and just >>>>>>>> wait for >>>> the >>>>>>>> successful submission. If we block for streaming queries, how >>>>>>>> can we >>>>>>>> collect() or print() results? >>>>>>>> >>>>>>>> Also, if we block for streaming queries, we could never support >>>>>>>> multiline files. Because the first INSERT INTO would block the >>> further >>>>>>>> execution. >>>>>>>> >>>>>>>> If we decide to block entirely on streaming queries, we need the >>> async >>>>>>>> execution methods in the design already. However, I would >>>>>>>> rather go >>>> for >>>>>>>> non-blocking streaming queries. Also with the `EMIT STREAM` key >>>>>>>> word >>>> in >>>>>>>> mind that we might add to SQL statements soon. >>>>>>>> >>>>>>>> Regards, >>>>>>>> Timo >>>>>>>> >>>>>>>> [1] https://issues.apache.org/jira/browse/FLINK-16761 >>>>>>>> [2] https://issues.apache.org/jira/browse/FLINK-12214 >>>>>>>> >>>>>>>> On 25.03.20 16:30, godfrey he wrote: >>>>>>>>> Hi Timo, >>>>>>>>> >>>>>>>>> Thanks for the updating. >>>>>>>>> >>>>>>>>> Regarding to "multiline statement support", I'm also fine that >>>>>>>>> `TableEnvironment.executeSql()` only supports single line >>> statement, >>>>>> and >>>>>>>> we >>>>>>>>> can support multiline statement later (needs more discussion >>>>>>>>> about >>>>>> this). >>>>>>>>> >>>>>>>>> Regarding to "StatementSet.explian()", I don't have strong >>>>>>>>> opinions >>>>>> about >>>>>>>>> that. >>>>>>>>> >>>>>>>>> Regarding to "TableResult.getJobClient()", I think it's >>> unnecessary. >>>>>> The >>>>>>>>> reason is: first, many statements (e.g. DDL, show xx, use xx) >>>>>>>>> will >>>> not >>>>>>>>> submit a Flink job. second, `TableEnvironment.executeSql()` and >>>>>>>>> `StatementSet.execute()` are synchronous method, `TableResult` >>>>>>>>> will >>>> be >>>>>>>>> returned only after the job is finished or failed. >>>>>>>>> >>>>>>>>> Regarding to "whether StatementSet.execute() needs to throw >>>>>> exception", I >>>>>>>>> think we should choose a unified way to tell whether the >>>>>>>>> execution >>> is >>>>>>>>> successful. If `TableResult` contains ERROR kind (non-runtime >>>>>> exception), >>>>>>>>> users need to not only check the result but also catch the >>>>>>>>> runtime >>>>>>>>> exception in their code. or `StatementSet.execute()` does not >>>>>>>>> throw >>>> any >>>>>>>>> exception (including runtime exception), all exception >>>>>>>>> messages are >>>> in >>>>>>>> the >>>>>>>>> result. I prefer "StatementSet.execute() needs to throw >>> exception". >>>> cc >>>>>>>> @Jark >>>>>>>>> Wu <[hidden email]> >>>>>>>>> >>>>>>>>> I will update the agreed parts to the document first. >>>>>>>>> >>>>>>>>> Best, >>>>>>>>> Godfrey >>>>>>>>> >>>>>>>>> >>>>>>>>> Timo Walther <[hidden email]> 于2020年3月25日周三 >>>>>>>>> 下午6:51写道： >>>>>>>>> >>>>>>>>>> Hi Godfrey, >>>>>>>>>> >>>>>>>>>> thanks for starting the discussion on the mailing list. And >>>>>>>>>> sorry >>>>>> again >>>>>>>>>> for the late reply to FLIP-84. I have updated the Google doc one >>>> more >>>>>>>>>> time to incorporate the offline discussions. >>>>>>>>>> >>>>>>>>>> From Dawid's and my view, it is fine to postpone the >>>>>>>>>> multiline >>>>>> support >>>>>>>>>> to a separate method. This can be future work even though we >>>>>>>>>> will >>>> need >>>>>>>>>> it rather soon. >>>>>>>>>> >>>>>>>>>> If there are no objections, I suggest to update the FLIP-84 >>>>>>>>>> again >>>> and >>>>>>>>>> have another voting process. >>>>>>>>>> >>>>>>>>>> Thanks, >>>>>>>>>> Timo >>>>>>>>>> >>>>>>>>>> >>>>>>>>>> On 25.03.20 11:17, godfrey he wrote: >>>>>>>>>>> Hi community, >>>>>>>>>>> Timo, Fabian and Dawid have some feedbacks about FLIP-84[1]. >>>>>>>>>>> The >>>>>>>>>> feedbacks >>>>>>>>>>> are all about new introduced methods. We had a discussion >>>> yesterday, >>>>>>>> and >>>>>>>>>>> most of feedbacks have been agreed upon. Here is the >>>>>>>>>>> conclusions: >>>>>>>>>>> >>>>>>>>>>> *1. about proposed methods in `TableEnvironment`:* >>>>>>>>>>> >>>>>>>>>>> the original proposed methods: >>>>>>>>>>> >>>>>>>>>>> TableEnvironment.createDmlBatch(): DmlBatch >>>>>>>>>>> TableEnvironment.executeStatement(String statement): >>>>>>>>>>> ResultTable >>>>>>>>>>> >>>>>>>>>>> the new proposed methods: >>>>>>>>>>> >>>>>>>>>>> // we should not use abbreviations in the API, and the term >>> "Batch" >>>>>> is >>>>>>>>>>> easily confused with batch/streaming processing >>>>>>>>>>> TableEnvironment.createStatementSet(): StatementSet >>>>>>>>>>> >>>>>>>>>>> // every method that takes SQL should have `Sql` in its name >>>>>>>>>>> // supports multiline statement ??? >>>>>>>>>>> TableEnvironment.executeSql(String statement): TableResult >>>>>>>>>>> >>>>>>>>>>> // new methods. supports explaining DQL and DML >>>>>>>>>>> TableEnvironment.explainSql(String statement, ExplainDetail... >>>>>>>> details): >>>>>>>>>>> String >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> *2. about proposed related classes:* >>>>>>>>>>> >>>>>>>>>>> the original proposed classes: >>>>>>>>>>> >>>>>>>>>>> interface DmlBatch { >>>>>>>>>>> void addInsert(String insert); >>>>>>>>>>> void addInsert(String targetPath, Table table); >>>>>>>>>>> ResultTable execute() throws Exception ; >>>>>>>>>>> String explain(boolean extended); >>>>>>>>>>> } >>>>>>>>>>> >>>>>>>>>>> public interface ResultTable { >>>>>>>>>>> TableSchema getResultSchema(); >>>>>>>>>>> Iterable<Row> getResultRows(); >>>>>>>>>>> } >>>>>>>>>>> >>>>>>>>>>> the new proposed classes: >>>>>>>>>>> >>>>>>>>>>> interface StatementSet { >>>>>>>>>>> // every method that takes SQL should have `Sql` in >>>>>>>>>>> its >>>> name >>>>>>>>>>> // return StatementSet instance for fluent programming >>>>>>>>>>> addInsertSql(String statement): StatementSet >>>>>>>>>>> >>>>>>>>>>> // return StatementSet instance for fluent programming >>>>>>>>>>> addInsert(String tablePath, Table table): StatementSet >>>>>>>>>>> >>>>>>>>>>> // new method. support overwrite mode >>>>>>>>>>> addInsert(String tablePath, Table table, boolean >>>> overwrite): >>>>>>>>>>> StatementSet >>>>>>>>>>> >>>>>>>>>>> explain(): String >>>>>>>>>>> >>>>>>>>>>> // new method. supports adding more details for the >>> result >>>>>>>>>>> explain(ExplainDetail... extraDetails): String >>>>>>>>>>> >>>>>>>>>>> // throw exception ??? >>>>>>>>>>> execute(): TableResult >>>>>>>>>>> } >>>>>>>>>>> >>>>>>>>>>> interface TableResult { >>>>>>>>>>> getTableSchema(): TableSchema >>>>>>>>>>> >>>>>>>>>>> // avoid custom parsing of an "OK" row in programming >>>>>>>>>>> getResultKind(): ResultKind >>>>>>>>>>> >>>>>>>>>>> // instead of `get` make it explicit that this is >>>>>>>>>>> might >>> be >>>>>>>>>> triggering >>>>>>>>>>> an expensive operation >>>>>>>>>>> collect(): Iterable<Row> >>>>>>>>>>> >>>>>>>>>>> // for fluent programming >>>>>>>>>>> print(): Unit >>>>>>>>>>> } >>>>>>>>>>> >>>>>>>>>>> enum ResultKind { >>>>>>>>>>> SUCCESS, // for DDL, DCL and statements with a simple >>> "OK" >>>>>>>>>>> SUCCESS_WITH_CONTENT, // rows with important >>>>>>>>>>> content are >>>>>>>> available >>>>>>>>>>> (DML, DQL) >>>>>>>>>>> } >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> *3. new proposed methods in `Table`* >>>>>>>>>>> >>>>>>>>>>> `Table.insertInto()` will be deprecated, and the following >>> methods >>>>>> are >>>>>>>>>>> introduced: >>>>>>>>>>> >>>>>>>>>>> Table.executeInsert(String tablePath): TableResult >>>>>>>>>>> Table.executeInsert(String tablePath, boolean overwrite): >>>> TableResult >>>>>>>>>>> Table.explain(ExplainDetail... details): String >>>>>>>>>>> Table.execute(): TableResult >>>>>>>>>>> >>>>>>>>>>> There are two issues need further discussion, one is whether >>>>>>>>>>> `TableEnvironment.executeSql(String statement): TableResult` >>> needs >>>> to >>>>>>>>>>> support multiline statement (or whether `TableEnvironment` >>>>>>>>>>> needs >>> to >>>>>>>>>> support >>>>>>>>>>> multiline statement), and another one is whether >>>>>>>> `StatementSet.execute()` >>>>>>>>>>> needs to throw exception. >>>>>>>>>>> >>>>>>>>>>> please refer to the feedback document [2] for the details. >>>>>>>>>>> >>>>>>>>>>> Any suggestions are warmly welcomed! >>>>>>>>>>> >>>>>>>>>>> [1] >>>>>>>>>>> >>>>>>>>>> >>>>>>>> >>>>>> >>>> >>> https://wiki.apache.org/confluence/pages/viewpage.action?pageId=134745878 >>> >>>>>>>>>>> [2] >>>>>>>>>>> >>>>>>>>>> >>>>>>>> >>>>>> >>>> >>> https://docs.google.com/document/d/1ueLjQWRPdLTFB_TReAyhseAX-1N3j4WYWD0F02Uau0E/edit >>> >>>>>>>>>>> >>>>>>>>>>> Best, >>>>>>>>>>> Godfrey >>>>>>>>>>> >>>>>>>>>> >>>>>>>>>> >>>>>>>>> >>>>>>>> >>>>>>>> >>>>>>> >>>>>> >>>>>> >>>>> >>>> >>>> >>> >> > |
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Re: [DISCUSS] FLIP-84 Feedback Summary
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Re: [DISCUSS] FLIP-84 Feedback Summary
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Re: [DISCUSS] FLIP-84 Feedback Summary
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Re: [DISCUSS] FLIP-84 Feedback Summary
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Re: [DISCUSS] FLIP-84 Feedback Summary
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When considering the multi-line support I think it is helpful to start with a use case in mind. In my opinion consumers of this method will be:
@Godfrey As for the quit/source/... commands. I think those belong to the responsibility of aforementioned. I think they should not be understandable by the TableEnvironment. What would quit on a TableEnvironment do? Moreover I think such commands should be prefixed appropriately. I think it's a common practice to e.g. prefix those with ! or : to say they are meta commands of the tool rather than a query. I also don't necessarily understand why platform users need to
know the kind of the query to use the proposed method. They should
get the type from the TableResult#ResultKind. If the ResultKind is
SUCCESS, it was a DCL/DDL. If SUCCESS_WITH_CONTENT it was a
DML/DQL. If that's not enough we can enrich the TableResult with
more explicit kind of query, but so far I don't see such a need. @Kurt In those cases I would assume the developers want to
present results of the queries anyway. Moreover I think it is safe
to assume they can adhere to such a contract that the results must
be iterated. For direct users of TableEnvironment/Table API this method does not make much sense anyway, in my opinion. I think we can rather safely assume in this scenario they do not want to submit multiple queries at a single time. Best, Dawid
On 01/04/2020 15:07, Kurt Young wrote:
One comment to `executeMultilineSql`, I'm afraid sometimes user might forget to iterate the returned iterators, e.g. user submits a bunch of DDLs and expect the framework will execute them one by one. But it didn't. Best, Kurt On Wed, Apr 1, 2020 at 5:10 PM Aljoscha Krettek [hidden email] wrote:Agreed to what Dawid and Timo said. To answer your question about multi line SQL: no, we don't think we need this in Flink 1.11, we only wanted to make sure that the interfaces that we now put in place will potentially allow this in the future. Best, Aljoscha On 01.04.20 09:31, godfrey he wrote:Hi, Timo & Dawid, Thanks so much for the effort of `multiline statements supporting`, I have a few questions about this method: 1. users can well control the execution logic through the proposed method if they know what the statements are (a statement is a DDL, a DML or others). but if a statement is from a file, that means users do not know what the statements are, the execution behavior is unclear. As a platform user, I think this method is hard to use, unless theplatformdefines a set of rule about the statements order, such as: no select in themiddle,dml must be at tail of sql file (which may be the most case in product env). Otherwise the platform must parse the sql first, then know what the statements are. If do like that, the platform can handle all cases through `executeSql`and`StatementSet`. 2. SQL client can't also use `executeMultilineSql` to supports multiline statements, because there are some special commands introduced in SQL client, such as `quit`, `source`, `load jar` (not exist now, but maybe we needthiscommand to support dynamic table source and udf). Does TableEnvironment also supports those commands? 3. btw, we must have this feature in release-1.11? I find there are few user cases in the feedback document which behavior is unclear now. regarding to "change the return value from `Iterable<Row` to `Iterator<Row`", I couldn't agree more with this change. Just as Dawid mentioned "The contract of the Iterable#iterator is that it returns a new iterator each time, which effectively means we can iterate the results multiple times.", we does not provide iterate the results multiple times. If we want do that, the client must buffer all results. but it'simpossiblefor streaming job. Best, Godfrey Dawid Wysakowicz [hidden email] 于2020年4月1日周三 上午3:14写道：Thank you Timo for the great summary! It covers (almost) all the topics. Even though in the end we are not suggesting much changes to the current state of FLIP I think it is important to lay out all possible use cases so that we do not change the execution model every release. There is one additional thing we discussed. Could we change the result type of TableResult#collect to Iterator<Row>? Even though those interfaces do not differ much. I think Iterator better describes that the results might not be materialized on the client side, but can be retrieved on a per record basis. The contract of the Iterable#iterator is that it returns a new iterator each time, which effectively means we can iterate the results multiple times. Iterating the results is not possible when we don't retrieve all the results from the cluster atonce.I think we should also use Iterator for TableEnvironment#executeMultilineSql(String statements): Iterator<TableResult>. Best, Dawid On 31/03/2020 19:27, Timo Walther wrote:Hi Godfrey, Aljoscha, Dawid, Klou, and I had another discussion around FLIP-84. In particular, we discussed how the current status of the FLIP and the future requirements around multiline statements, async/sync, collect() fit together. We also updated the FLIP-84 Feedback Summary document [1] with some use cases. We believe that we found a good solution that also fits to what is in the current FLIP. So no bigger changes necessary, which is great! Our findings were: 1. Async vs sync submission of Flink jobs: Having a blocking `execute()` in DataStream API was rather a mistake. Instead all submissions should be async because this allows supporting both modes if necessary. Thus, submitting all queries async sounds good to us. If users want to run a job sync, they can use the JobClient and wait for completion (or collect() in case of batch jobs). 2. Multi-statement execution: For the multi-statement execution, we don't see a contradication with the async execution behavior. We imagine a method like: TableEnvironment#executeMultilineSql(String statements): Iterable<TableResult> Where the `Iterator#next()` method would trigger the next statement submission. This allows a caller to decide synchronously when to submit statements async to the cluster. Thus, a service such as the SQL Client can handle the result of each statement individually and process statement by statement sequentially. 3. The role of TableResult and result retrieval in general `TableResult` is similar to `JobClient`. Instead of returning a `CompletableFuture` of something, it is a concrete util class where some methods have the behavior of completable future (e.g. collect(), print()) and some are already completed (getTableSchema(), getResultKind()). `StatementSet#execute()` returns a single `TableResult` because the order is undefined in a set and all statements have the same schema. Its `collect()` will return a row for each executed `INSERT INTO` in the order of statement definition. For simple `SELECT * FROM ...`, the query execution might block until `collect()` is called to pull buffered rows from the job (from socket/REST API what ever we will use in the future). We can say that a statement finished successfully, when the `collect#Iterator#hasNext` has returned false. I hope this summarizes our discussion @Dawid/Aljoscha/Klou? It would be great if we can add these findings to the FLIP before we start voting. One minor thing: some `execute()` methods still throw a checked exception; can we remove that from the FLIP? Also the above mentioned `Iterator#next()` would trigger an execution without throwing a checked exception. Thanks, Timo [1]https://docs.google.com/document/d/1ueLjQWRPdLTFB_TReAyhseAX-1N3j4WYWD0F02Uau0E/edit#On 31.03.20 06:28, godfrey he wrote:Hi, Timo & Jark Thanks for your explanation. Agree with you that async execution should always be async, and sync execution scenario can be covered by async execution. It helps provide an unified entry point for batch and streaming. I think we can also use sync execution for some testing. So, I agree with you that we provide `executeSql` method and it'sasyncmethod. If we want sync method in the future, we can add method named `executeSqlSync`. I think we've reached an agreement. I will update the document, and start voting process. Best, Godfrey Jark Wu [hidden email] 于2020年3月31日周二 上午12:46写道：Hi, I didn't follow the full discussion. But I share the same concern with Timo that streaming queries should always be async. Otherwise, I can image it will cause a lot of confusion and problemsifusers don't deeply keep the "sync" in mind (e.g. client hangs). Besides, the streaming mode is still the majority use cases of Flink and Flink SQL. We should put the usability at a high priority. Best, Jark On Mon, 30 Mar 2020 at 23:27, Timo Walther [hidden email]wrote:Hi Godfrey, maybe I wasn't expressing my biggest concern enough in my last mail. Even in a singleline and sync execution, I think that streaming queries should not block the execution. Otherwise it is not possible to call collect() or print() on them afterwards. "there are too many things need to discuss for multiline": True, I don't want to solve all of them right now. But what I knowisthat our newly introduced methods should fit into a multiline execution. There is no big difference of calling `executeSql(A), executeSql(B)` and processing a multiline file `A;\nB;`. I think the example that you mentioned can simply be undefined for now. Currently, no catalog is modifying data but just metadata. This is a separate discussion. "result of the second statement is indeterministic": Sure this is indeterministic. But this is the implementers fault and we cannot forbid such pipelines. How about we always execute streaming queries async? It wouldunblockexecuteSql() and multiline statements. Having a `executeSqlAsync()` is useful for batch. However, I don't want `sync/async` be the new batch/stream flag. The execution behavior should come from the query itself. Regards, Timo On 30.03.20 11:12, godfrey he wrote:Hi Timo, Agree with you that streaming queries is our top priority, but I think there are too many things need to discuss for multiline statements: e.g. 1. what's the behaivor of DDL and DML mixing for async execution: create table t1 xxx; create table t2 xxx; insert into t2 select * from t1 where xxx; drop table t1; // t1 may be a MySQL table, the data will also bedeleted.t1 is dropped when "insert" job is running. 2. what's the behaivor of unified scenario for async execution: (as you mentioned) INSERT INTO t1 SELECT * FROM s; INSERT INTO t2 SELECT * FROM s JOIN t1 EMIT STREAM; The result of the second statement is indeterministic, because thefirststatement maybe is running. I think we need to put a lot of effort to define the behavior oflogicallyrelated queries. In this FLIP, I suggest we only handle single statement, and wealsointroduce an async execute method which is more important and more often used for users. Dor the sync methods (like `TableEnvironment.executeSql` and `StatementSet.execute`), the result will be returned until the job is finished. Thefollowing |
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