Multiple batch joins on the same key results in multiple shuffles

[kennknowles]

The query like this:

SELECT a.*, b.*, c.* FROM a JOIN b ON a.some_id = b.some_id JOIN c ON a.some_id = c.some_id;

results in two shuffles. Can probably be optimized.

Relevant code:

• BeamJoinRel implements Join in SQL:

  beam/sdks/java/extensions/sql/src/main/java/org/apache/beam/sdk/extensions/sql/impl/rel/BeamJoinRel.java

  Line 194 in 1675b0f

  if ((leftRows.isBounded() == PCollection.IsBounded.BOUNDED

• CoGBK Join implementation:

  beam/sdks/java/extensions/join-library/src/main/java/org/apache/beam/sdk/extensions/joinlibrary/Join.java

  Line 36 in 279a056

  public class Join {

Imported from Jira BEAM-5049. Original Jira may contain additional context.
Reported by: kedin.

[AsmitBhardwaj]

Hi I would like to work on this issue