From: | tgl(at)svr1(dot)postgresql(dot)org (Tom Lane) |
---|---|
To: | pgsql-committers(at)postgresql(dot)org |
Subject: | pgsql: When dealing with multiple grouping columns coming from the same |
Date: | 2005-01-28 20:34:31 |
Message-ID: | 20050128203431.5D0263A60AB@svr1.postgresql.org |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-committers |
Log Message:
-----------
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.
Modified Files:
--------------
pgsql/src/backend/utils/adt:
selfuncs.c (r1.169 -> r1.170)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/selfuncs.c.diff?r1=1.169&r2=1.170)
pgsql/src/test/regress/expected:
subselect.out (r1.10 -> r1.11)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/subselect.out.diff?r1=1.10&r2=1.11)
From | Date | Subject | |
---|---|---|---|
Next Message | Tom Lane | 2005-01-28 20:35:21 | pgsql: When dealing with multiple grouping columns coming from the same |
Previous Message | Tom Lane | 2005-01-28 19:36:41 | pgsql: Improve planner's estimation of the space needed for HashAgg |