ygf11 opened a new pull request, #5087:
URL: https://github.com/apache/arrow-datafusion/pull/5087
# Which issue does this PR close?
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Closes #5022.
# Rationale for this change
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1. Currently the required distribution of `NestedLoopJoinExec` is not
consistent with `CrossJoinExec`, and some optimization(`JoinSelection`) already
done for `CrossJoinExec` will not take effect for `NestedLoopJoinExec`.
2. `NestedLoopJoinExec` will collect both left and right to a single
partition for `Full` join, this may cause performance issue.
We can always collect left for `NestedLoopJoinExec` like `CrossJoinExec`
does.
# What changes are included in this PR?
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1. Always collect left side for `NestedLoopJoinExec` like `CrossJoinExec`
does.
2. For `LEFT/LEFT-SEMI/LEFT-ANTI/FULL`, we need generate the additional data
for the unmatched rows, so maintain a global state of `visited_left_side` in
`NestedLoopJoinExec`.
3. Merge partition state - `visited_left_side` to global after one partition
is finished.
4. Generate the additional data for the unmatched rows based on `global
state` after all partition is finished.
# Are these changes tested?
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# Are there any user-facing changes?
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