From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | pgsql-committers(at)postgresql(dot)org |
Subject: | pgsql: Improve eqjoinsel's ndistinct clamping to work for multiple leve |
Date: | 2011-08-31 20:06:13 |
Message-ID: | E1Qyr37-0001zq-N5@gemulon.postgresql.org |
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Lists: | pgsql-committers |
Improve eqjoinsel's ndistinct clamping to work for multiple levels of join.
This patch fixes an oversight in my commit
7f3eba30c9d622d1981b1368f2d79ba0999cdff2 of 2008-10-23. That patch
accounted for baserel restriction clauses that reduced the number of rows
coming out of a table (and hence the number of possibly-distinct values of
a join variable), but not for join restriction clauses that might have been
applied at a lower level of join. To account for the latter, look up the
sizes of the min_lefthand and min_righthand inputs of the current join,
and clamp with those in the same way as for the base relations.
Noted while investigating a complaint from Ben Chobot, although this in
itself doesn't seem to explain his report.
Back-patch to 8.4; previous versions used different estimation methods
for which this heuristic isn't relevant.
Branch
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master
Details
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http://git.postgresql.org/pg/commitdiff/97930cf578e28c01f67fe4006ffcdbb5aedf18c2
Modified Files
--------------
src/backend/utils/adt/selfuncs.c | 81 ++++++++++++++++++++++++++++++++++----
1 files changed, 73 insertions(+), 8 deletions(-)
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