Hello Anurag Mantripragada, Vihang Karajgaonkar, Impala Public Jenkins,
I'd like you to reexamine a change. Please visit
http://gerrit.cloudera.org:8080/15157
to look at the new patch set (#2).
Change subject: IMPALA-9358: Query slowdown with inline views and hundreds of
columns
......................................................................
IMPALA-9358: Query slowdown with inline views and hundreds of columns
IMPALA-8386 introduced an expensive precondition check using the function
ExprSubstitutionMap.checkComposedFrom(). This check has significant
performance impact on statements that contain inline views with hundreds
of columns. Most of the cost is in the get() calls used to find
expressions in the local substitution map.
The fix is to add a get_hint() call that uses the current loop index as a
starting point to search for expressions. This leverages the fact that
expressions have identical positions in both substitution maps in most
common cases.
A more generic approach would be to accelerate expression equality search
using hash functions but that would be a much riskier fix and Impala
currently lacks the infrasturucture to so.
Testing:
Performance testing with a query with 1000 expressions of the
following form:
with a as (select c1 c1, c1 c2, c1 c3, ... from t)
select c1, c2, c3, ... from a;
Change-Id: I77423d9c10e1edbb505cb210b5c072281b5d7cfc
---
M fe/src/main/java/org/apache/impala/analysis/ExprSubstitutionMap.java
1 file changed, 16 insertions(+), 2 deletions(-)
git pull ssh://gerrit.cloudera.org:29418/Impala-ASF refs/changes/57/15157/2
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Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-MessageType: newpatchset
Gerrit-Change-Id: I77423d9c10e1edbb505cb210b5c072281b5d7cfc
Gerrit-Change-Number: 15157
Gerrit-PatchSet: 2
Gerrit-Owner: Kurt Deschler <kdesc...@cloudera.com>
Gerrit-Reviewer: Anurag Mantripragada <anu...@cloudera.com>
Gerrit-Reviewer: Impala Public Jenkins <impala-public-jenk...@cloudera.com>
Gerrit-Reviewer: Kurt Deschler <kdesc...@cloudera.com>
Gerrit-Reviewer: Vihang Karajgaonkar <vih...@cloudera.com>
