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https://issues.apache.org/jira/browse/DERBY-6938?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16088752#comment-16088752
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Bryan Pendleton commented on DERBY-6938:
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Hi Vardhan,
I think your observation about the Optimizer being unwilling to choose Hash
Join plans if it believes they will not fit in memory is very interesting. Our
documentation
(https://db.apache.org/derby/docs/10.13/tuning/ctunoptimz23173.html) definitely
claims that Derby will choose a hash join, and will spill to disk if the join
is larger than will fit in memory, and I believe that was definitely the intent
of DERBY-106.
But it appears that it isn't working as we expect.
In researching this, I came across a very interesting discussion in DERBY-4620.
Perhaps you could look through the DERBY-4620 work, and see if you have any
additional observations to share regarding the behavior that you see?
> Obtain cardinality estimates and true estimates for base tables as well as
> for intermediate results for queries involving multiple joins.
> -------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: DERBY-6938
> URL: https://issues.apache.org/jira/browse/DERBY-6938
> Project: Derby
> Issue Type: Sub-task
> Components: SQL
> Reporter: Harshvardhan Gupta
> Assignee: Harshvardhan Gupta
> Attachments: explain.txt
>
>
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