From: | tgl(at)svr1(dot)postgresql(dot)org (Tom Lane) |
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To: | pgsql-committers(at)postgresql(dot)org |
Subject: | pgsql: When dealing with multiple grouping columns coming from the same |
Date: | 2005-01-28 20:35:21 |
Message-ID: | 20050128203521.3BE033A606F@svr1.postgresql.org |
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Lists: | pgsql-committers |
Log Message:
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When dealing with multiple grouping columns coming from the same table,
clamp the estimated number of groups to table row count over 10, instead
of table row count; this reflects a heuristic that people probably won't
group over a near-unique set of columns, and the knowledge that we don't
currently have any way to estimate the correlation of the columns better
than guessing. This change creates a trivial plan change in one of the
regression tests.
Tags:
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REL8_0_STABLE
Modified Files:
--------------
pgsql/src/backend/utils/adt:
selfuncs.c (r1.169 -> r1.169.4.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/selfuncs.c.diff?r1=1.169&r2=1.169.4.1)
pgsql/src/test/regress/expected:
subselect.out (r1.10 -> r1.10.4.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/subselect.out.diff?r1=1.10&r2=1.10.4.1)
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