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https://issues.apache.org/jira/browse/IMPALA-13660?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Work on IMPALA-13660 stopped by Michael Smith.
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> Cache broadcast hash joins
> --------------------------
>
> Key: IMPALA-13660
> URL: https://issues.apache.org/jira/browse/IMPALA-13660
> Project: IMPALA
> Issue Type: Improvement
> Reporter: Michael Smith
> Assignee: Michael Smith
> Priority: Major
>
> Enable intermediate result caching for broadcast hash joins. The cache key
> must incorporate probe and build sides; since the build side will be part of
> the cache key, we can rely on the broadcast results being stable.
> This differs from a partition join, where we don't have the same guarantees;
> partition joins would also incorporate an exchange on the probe side, so our
> normal rules would preclude caching it right now.
> The build side comes from another fragment, so we need to tolerate an
> exchange on the build side, similar to what was done in IMPALA-13185.
> We need to make sure cached results are returned immediately when available
> rather than waiting on a build side we don't need; also make sure the build
> side can complete even if its results are not needed by any joins (because
> they all had cache hits). It would be nice to cancel the build side fragment
> if a cache hit is identified on all join fragments, since the build side
> results would no longer be needed.
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