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https://issues.apache.org/jira/browse/IMPALA-7836?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16690195#comment-16690195
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ASF subversion and git services commented on IMPALA-7836:
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Commit 3dea93ef0f364325dff2893642d5516a4ecd16bd in impala's branch
refs/heads/master from [~arodoni_cloudera]
[ https://git-wip-us.apache.org/repos/asf?p=impala.git;h=3dea93e ]
IMPALA-7836: [DOCS] Format changes in impala_topn_bytes_limit.xml
Change-Id: I731b26fe2c225e706454f16cd3b6de697ec70fe2
Reviewed-on: http://gerrit.cloudera.org:8080/11935
Reviewed-by: Alex Rodoni <[email protected]>
Tested-by: Impala Public Jenkins <[email protected]>
> Impala 3.1 Doc: New query option 'topn_bytes_limit' for TopN to Sort
> conversion
> -------------------------------------------------------------------------------
>
> Key: IMPALA-7836
> URL: https://issues.apache.org/jira/browse/IMPALA-7836
> Project: IMPALA
> Issue Type: Sub-task
> Components: Docs, Frontend
> Affects Versions: Impala 2.9.0
> Reporter: Sahil Takiar
> Assignee: Alex Rodoni
> Priority: Major
> Labels: future_release_doc
> Fix For: Impala 3.1.0
>
>
> IMPALA-5004 adds a new query level option called 'topn_bytes_limit' that we
> should document. The changes in IMPALA-5004 work by estimating the amount of
> memory required to run a TopN operator. The memory estimate is based on the
> size of the individual tuples that need to be processed by the TopN operator,
> as well as the sum of the limit and offset in the query. TopN operators don't
> spill to disk so they have to keep all rows they process in memory.
> If the estimated size of the working set of the TopN operator exceeds the
> threshold of 'topn_bytes_limit' the TopN operator will be replaced with a
> Sort operator. The Sort operator can spill to disk, but it processes all the
> data (the limit and offset have no affect). So switching to Sort might incur
> performance penalties, but it will require less memory.
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