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From "Tianyi Wang (Code Review)" <>
Subject [Impala-ASF-CR] IMPALA-4794: Grouping distinct agg plan robust to data skew
Date Mon, 14 Aug 2017 21:01:13 GMT
Tianyi Wang has uploaded a new patch set (#3).

Change subject: IMPALA-4794: Grouping distinct agg plan robust to data skew

IMPALA-4794: Grouping distinct agg plan robust to data skew

This patch changes the query plan for grouping distinct aggregations to
be more robust to data skew in the grouping expressions. The existing
plan partitions data between phase-1 and phase-2 by grouping expr and
the data skewness on grouping expr directly impacts performance. The
new plan partitions data by both grouping expr and distinct aggregation
expr, then adds one more aggregation and exchange node. It is supposed
to be faster with data skew but slower otherwise.

Teting: Modified existing planner tests which already provide sufficient
coverage. The pattern is that the distinct aggregation expr is added to
exchange node, followed by an additional merge aggregation and exchange

Change-Id: I7bdada0e328b555900c7b7ff8aabc8eb15ae8fa9
M fe/src/main/java/org/apache/impala/planner/
M testdata/workloads/functional-planner/queries/PlannerTest/aggregation.test
M testdata/workloads/functional-planner/queries/PlannerTest/distinct.test
M testdata/workloads/functional-planner/queries/PlannerTest/insert.test
M testdata/workloads/functional-planner/queries/PlannerTest/kudu.test
M testdata/workloads/functional-planner/queries/PlannerTest/tpch-all.test
M testdata/workloads/functional-planner/queries/PlannerTest/tpch-nested.test
7 files changed, 215 insertions(+), 131 deletions(-)

  git pull ssh:// refs/changes/43/7643/3
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Gerrit-MessageType: newpatchset
Gerrit-Change-Id: I7bdada0e328b555900c7b7ff8aabc8eb15ae8fa9
Gerrit-PatchSet: 3
Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-Owner: Tianyi Wang <>
Gerrit-Reviewer: Alex Behm <>
Gerrit-Reviewer: Tianyi Wang <>

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