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https://issues.apache.org/jira/browse/DERBY-3002?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12724829#action_12724829
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Knut Anders Hatlen commented on DERBY-3002:
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Hi Bryan,
I'm not aware of any GROUP BY benchmarks that we can use, so I guess we'll have
to write a simple one ourselves. The reason why I asked was that it wasn't
quite clear to me (well, it still isn't... :)) whether your comment about
aggregate sort observers being an efficient technique meant that you thought
the new technique was less efficient.
As to the hash tables, one alternative is to use a BackingStoreHashTable, which
keeps the data in a HashMap up to a certain point, after which it spills data
to disk (or at least to the page cache). It'll probably increase the overhead,
though.
> Add support for GROUP BY ROLLUP
> -------------------------------
>
> Key: DERBY-3002
> URL: https://issues.apache.org/jira/browse/DERBY-3002
> Project: Derby
> Issue Type: New Feature
> Components: SQL
> Affects Versions: 10.4.1.3
> Reporter: Bryan Pendleton
> Assignee: Bryan Pendleton
> Priority: Minor
> Attachments: fixWhiteSpace.diff, IncludesASimpleTest.diff,
> passesRegressionTests.diff, prototypeChangeNoTests.diff,
> rewriteGroupByRS.diff, rollupNullability.diff, useLookahead.diff
>
>
> Provide an implementation of the ROLLUP form of multi-dimensional grouping
> according to the SQL standard.
> See http://wiki.apache.org/db-derby/OLAPRollupLists for some more detailed
> information about this aspect of the SQL standard.
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