ngsg opened a new pull request, #6007:
URL: https://github.com/apache/hive/pull/6007
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### What changes were proposed in this pull request?
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This patch modifies `HiveSubQueryRemoveRule` to use InnerJoin instead of
SemiJoin for uncorrelated IN/EXISTS subqueries with `logic ==
RelOptUtil.Logic.TRUE`. This restores the logic in
`HiveSubQRemoveRelBuilder$join`, which is replaced by Calcite's RelBuilder.
### Why are the changes needed?
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To restore the previous logic and increase the chances of applying
optimizations to the query plan.
We started using SemiJoin in `HiveSubQueryRemoveRule` with HIVE-17767, which
introduced SemiJoin for correlated subqueries in conjunction with removing the
input Aggregate. Since HIVE-24685, we have been using SemiJoin for both
uncorrelated and correlated subqueries, but we currently do not remove the
input Aggregate for uncorrelated subqueries.
In addition, some optimization rules are not applicable to HiveSemiJoin,
which reduces the chances of finding an optimal plan. Therefore, I suggest
restoring the previous logic by using InnerJoin for uncorrelated cases.
### Does this PR introduce _any_ user-facing change?
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No
### How was this patch tested?
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I added a new `EXPLAIN CBO` query with uncorrelated IN subquery in
`subquery_in.q` to check whether join reordering is applied. One can verify
that CalcitePlanner produces a query plan with a different join order when this
patch is applied.
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