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From "Taras Bobrovytsky (Code Review)" <ger...@cloudera.org>
Subject [Impala-ASF-CR] IMPALA-4787: Optimize APPX MEDIAN() memory usage
Date Wed, 15 Feb 2017 23:49:44 GMT
Taras Bobrovytsky has uploaded a new change for review.

  http://gerrit.cloudera.org:8080/6025

Change subject: IMPALA-4787: Optimize APPX_MEDIAN() memory usage
......................................................................

IMPALA-4787: Optimize APPX_MEDIAN() memory usage

Before this change, ReservoirSample functions (such as APPX_MEDIAN())
allocated memory for 20,000 elements up front per grouping key. This
caused inefficient memory usage for aggregations with many grouping
keys.

This patch fixes this by initially allocating memory for 20 elements.
Once the buffer becomes full, we allocate room for 200 elements and
copy the original buffer into the new one. We continue increasing the
buffer size this way until the buffer has room for 20,000 elements as
before.

Testing:
Ran BE and some relevant EE tests locally.
No new tests were added, the existing tests should provide enough
coverage.

Change-Id: I99adaad574d4fb0a3cf38c6cbad8b2a23df12968
---
M be/src/exprs/aggregate-functions-ir.cc
1 file changed, 124 insertions(+), 30 deletions(-)


  git pull ssh://gerrit.cloudera.org:29418/Impala-ASF refs/changes/25/6025/1
-- 
To view, visit http://gerrit.cloudera.org:8080/6025
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Gerrit-MessageType: newchange
Gerrit-Change-Id: I99adaad574d4fb0a3cf38c6cbad8b2a23df12968
Gerrit-PatchSet: 1
Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-Owner: Taras Bobrovytsky <tbobrovytsky@cloudera.com>

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