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Posted to issues@flink.apache.org by "gustavodemorais (via GitHub)" <gi...@apache.org> on 2025/11/25 13:00:22 UTC
[PR] [FLINK-38731][table] Add support for MULTI_JOIN hint [flink]
gustavodemorais opened a new pull request, #27271:
URL: https://github.com/apache/flink/pull/27271
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## What is the purpose of the change
We want to expose the MultiJoin operator via a hint so that users can control which tables are merged into a MultiJoin and which ones should continue to use the regular join operator. The user can then control wether only some tables or all tables should be merged into the MultiJoin. The existing common join key restrictions continue to apply. The hint can be used in combination with the STATE_TTL hint as well.
## Brief change log
- Introduce MULTI_JOIN hint
- Adjust Join to MultiJoin rule
- Add documentation to tunind and hints
## Verifying this change
- Added multiple plan tests to check if the proper plans are created
- Added semantic test to check if execution and results are correct
## Does this pull request potentially affect one of the following parts:
- Dependencies (does it add or upgrade a dependency): (no)
- The public API, i.e., is any changed class annotated with `@Public(Evolving)`: (no)
- The serializers: (no)
- The runtime per-record code paths (performance sensitive): (no)
- Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (no)
- The S3 file system connector: (no)
## Documentation
- Does this pull request introduce a new feature? (yes)
- If yes, how is the feature documented? (docs)
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Re: [PR] [FLINK-38731][table] Add support for MULTI_JOIN hint [flink]
Posted by "gustavodemorais (via GitHub)" <gi...@apache.org>.
gustavodemorais commented on code in PR #27271:
URL: https://github.com/apache/flink/pull/27271#discussion_r2564595215
##########
docs/content/docs/dev/table/sql/queries/hints.md:
##########
@@ -279,6 +279,49 @@ SELECT /*+ NEST_LOOP(t1) */ * FROM t1 JOIN t2 ON t1.id = t2.id;
SELECT /*+ NEST_LOOP(t1, t3) */ * FROM t1 JOIN t2 ON t1.id = t2.id JOIN t3 ON t1.id = t3.id;
```
+#### MULTI_JOIN
+
+{{< label Streaming >}}
+
+`MULTI_JOIN` suggests that Flink uses the `MultiJoin operator` to process multiple regular joins simultaneously. This type of join hint is recommended when you have multiple joins that share at least one common join key and experience large intermediate state or record amplification. The MultiJoin operator eliminates intermediate state by processing joins across various input streams simultaneously, which can significantly reduce state size and improve performance in some cases.
+
+For more details on the MultiJoin operator, including when to use it and configuration options, see [Multiple Regular Joins]({{< ref "docs/dev/table/tuning" >}}#multiple-regular-joins).
+
+{{< hint info >}}
+Note:
+- The MULTI_JOIN hint can specify table names or table aliases. If a table has an alias, the hint must use the alias name.
Review Comment:
I've opened another PR so we add this as a small note https://github.com/apache/flink/pull/27277/files
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Re: [PR] [FLINK-38731][table] Add support for MULTI_JOIN hint [flink]
Posted by "davidradl (via GitHub)" <gi...@apache.org>.
davidradl commented on code in PR #27271:
URL: https://github.com/apache/flink/pull/27271#discussion_r2565087858
##########
docs/content/docs/dev/table/sql/queries/hints.md:
##########
@@ -279,6 +279,49 @@ SELECT /*+ NEST_LOOP(t1) */ * FROM t1 JOIN t2 ON t1.id = t2.id;
SELECT /*+ NEST_LOOP(t1, t3) */ * FROM t1 JOIN t2 ON t1.id = t2.id JOIN t3 ON t1.id = t3.id;
```
+#### MULTI_JOIN
Review Comment:
@gustavodemorais the usual way is to add new files as English into the chinese section.
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Re: [PR] [FLINK-38731][table] Add support for MULTI_JOIN hint [flink]
Posted by "flinkbot (via GitHub)" <gi...@apache.org>.
flinkbot commented on PR #27271:
URL: https://github.com/apache/flink/pull/27271#issuecomment-3575541322
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## CI report:
* 90fac6461335a041ed795656d01056314375cc83 UNKNOWN
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Re: [PR] [FLINK-38731][table] Add support for MULTI_JOIN hint [flink]
Posted by "davidradl (via GitHub)" <gi...@apache.org>.
davidradl commented on code in PR #27271:
URL: https://github.com/apache/flink/pull/27271#discussion_r2564394617
##########
docs/content/docs/dev/table/sql/queries/hints.md:
##########
@@ -279,6 +279,49 @@ SELECT /*+ NEST_LOOP(t1) */ * FROM t1 JOIN t2 ON t1.id = t2.id;
SELECT /*+ NEST_LOOP(t1, t3) */ * FROM t1 JOIN t2 ON t1.id = t2.id JOIN t3 ON t1.id = t3.id;
```
+#### MULTI_JOIN
Review Comment:
Please add the Chinese version of this as well.
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Re: [PR] [FLINK-38731][table] Add support for MULTI_JOIN hint [flink]
Posted by "gustavodemorais (via GitHub)" <gi...@apache.org>.
gustavodemorais commented on code in PR #27271:
URL: https://github.com/apache/flink/pull/27271#discussion_r2564557600
##########
docs/content/docs/dev/table/sql/queries/hints.md:
##########
@@ -279,6 +279,49 @@ SELECT /*+ NEST_LOOP(t1) */ * FROM t1 JOIN t2 ON t1.id = t2.id;
SELECT /*+ NEST_LOOP(t1, t3) */ * FROM t1 JOIN t2 ON t1.id = t2.id JOIN t3 ON t1.id = t3.id;
```
+#### MULTI_JOIN
Review Comment:
I'll create a ticket for the community to pick it up since I have no Chinese knowledge to review the output of automatic translation
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Re: [PR] [FLINK-38731][table] Add support for MULTI_JOIN hint [flink]
Posted by "davidradl (via GitHub)" <gi...@apache.org>.
davidradl commented on code in PR #27271:
URL: https://github.com/apache/flink/pull/27271#discussion_r2564414457
##########
docs/content/docs/dev/table/sql/queries/hints.md:
##########
@@ -279,6 +279,49 @@ SELECT /*+ NEST_LOOP(t1) */ * FROM t1 JOIN t2 ON t1.id = t2.id;
SELECT /*+ NEST_LOOP(t1, t3) */ * FROM t1 JOIN t2 ON t1.id = t2.id JOIN t3 ON t1.id = t3.id;
```
+#### MULTI_JOIN
+
+{{< label Streaming >}}
+
+`MULTI_JOIN` suggests that Flink uses the `MultiJoin operator` to process multiple regular joins simultaneously. This type of join hint is recommended when you have multiple joins that share at least one common join key and experience large intermediate state or record amplification. The MultiJoin operator eliminates intermediate state by processing joins across various input streams simultaneously, which can significantly reduce state size and improve performance in some cases.
+
+For more details on the MultiJoin operator, including when to use it and configuration options, see [Multiple Regular Joins]({{< ref "docs/dev/table/tuning" >}}#multiple-regular-joins).
+
+{{< hint info >}}
+Note:
+- The MULTI_JOIN hint can specify table names or table aliases. If a table has an alias, the hint must use the alias name.
Review Comment:
We have the OptimizerConfigOptions.TABLE_OPTIMIZER_MULTI_JOIN_ENABLED table config and the hints now. If both are specified then I think we need to document and be clear on the precedence i.e. do the hints always get honoured if they are specified or does the table config win.
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Re: [PR] [FLINK-38731][table] Add support for MULTI_JOIN hint [flink]
Posted by "davidradl (via GitHub)" <gi...@apache.org>.
davidradl commented on code in PR #27271:
URL: https://github.com/apache/flink/pull/27271#discussion_r2564406659
##########
flink-table/flink-table-planner/src/main/scala/org/apache/flink/table/planner/plan/optimize/program/FlinkStreamProgram.scala:
##########
@@ -233,22 +233,20 @@ object FlinkStreamProgram {
}
// multi-join
- if (tableConfig.get(OptimizerConfigOptions.TABLE_OPTIMIZER_MULTI_JOIN_ENABLED)) {
Review Comment:
I am curious as to effect of removing this if. I would have expected the if to say if multi join is enabled in table config or there are hints then we should do multi join processing.
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Re: [PR] [FLINK-38731][table] Add support for MULTI_JOIN hint [flink]
Posted by "dawidwys (via GitHub)" <gi...@apache.org>.
dawidwys merged PR #27271:
URL: https://github.com/apache/flink/pull/27271
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Re: [PR] [FLINK-38731][table] Add support for MULTI_JOIN hint [flink]
Posted by "gustavodemorais (via GitHub)" <gi...@apache.org>.
gustavodemorais commented on code in PR #27271:
URL: https://github.com/apache/flink/pull/27271#discussion_r2564523708
##########
flink-table/flink-table-planner/src/main/scala/org/apache/flink/table/planner/plan/optimize/program/FlinkStreamProgram.scala:
##########
@@ -233,22 +233,20 @@ object FlinkStreamProgram {
}
// multi-join
- if (tableConfig.get(OptimizerConfigOptions.TABLE_OPTIMIZER_MULTI_JOIN_ENABLED)) {
Review Comment:
There are no effects because I moved the check to the rule https://github.com/apache/flink/pull/27271/files#diff-44d9c5d7695b96ec29f833777fcfd24c78c5e0a9d0dab52d4b5403ccd3a7d165R191
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