[jira] [Created] (IMPALA-9416) Reduce minimum reservation for shared broadcast join builders

["Tim Armstrong (Jira)" <ji...@apache.org>]

Tim Armstrong created IMPALA-9416:
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             Summary: Reduce minimum reservation for shared broadcast join builders
                 Key: IMPALA-9416
                 URL: https://issues.apache.org/jira/browse/IMPALA-9416
             Project: IMPALA
          Issue Type: Improvement
          Components: Frontend
            Reporter: Tim Armstrong


This is an optimisation that I'm deferring from IMPALA-9156. The initial version of IMPALA-9156 will be conservative in the amount of memory it reserves for the broadcast join builder.

We should make it more precise to avoid blowing up the memory requirements. Specifically:
* the reservation should depend on the number of consuming fragments scheduled, not mt_dop
* we may want to look at how to reduce the amount of memory reserved per probe side. E.g. use smaller buffer sizes for the probe streams, under the assumption that a broadcast join is unlikely to spill.



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