From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | pgsql-committers(at)postgresql(dot)org |
Subject: | pgsql: Weaken the planner's tests for relevant joinclauses. |
Date: | 2012-04-13 20:07:36 |
Message-ID: | E1SImmO-0001tv-Dz@gemulon.postgresql.org |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-committers |
Weaken the planner's tests for relevant joinclauses.
We should be willing to cross-join two small relations if that allows us
to use an inner indexscan on a large relation (that is, the potential
indexqual for the large table requires both smaller relations). This
worked in simple cases but fell apart as soon as there was a join clause
to a fourth relation, because the existence of any two-relation join clause
caused the planner to not consider clauseless joins between other base
relations. The added regression test shows an example case adapted from
a recent complaint from Benoit Delbosc.
Adjust have_relevant_joinclause, have_relevant_eclass_joinclause, and
has_relevant_eclass_joinclause to consider that a join clause mentioning
three or more relations is sufficient grounds for joining any subset of
those relations, even if we have to do so via a cartesian join. Since such
clauses are relatively uncommon, this shouldn't affect planning speed on
typical queries; in fact it should help a bit, because the latter two
functions in particular get significantly simpler.
Although this is arguably a bug fix, I'm not going to risk back-patching
it, since it might have currently-unforeseen consequences.
Branch
------
master
Details
-------
http://git.postgresql.org/pg/commitdiff/e3ffd05b02468b1a53de31a322cedf195576a625
Modified Files
--------------
src/backend/optimizer/path/equivclass.c | 96 ++++++-------------------------
src/backend/optimizer/path/joinrels.c | 14 ++---
src/backend/optimizer/util/joininfo.c | 24 ++++++--
src/test/regress/expected/join.out | 51 ++++++++++++++++
src/test/regress/sql/join.sql | 18 ++++++
5 files changed, 110 insertions(+), 93 deletions(-)
From | Date | Subject | |
---|---|---|---|
Next Message | Robert Haas | 2012-04-13 20:43:26 | pgsql: Add Peter Geoghegan as additional author of pg_stat_statements. |
Previous Message | Guillaume Lelarge | 2012-04-13 19:57:58 | Re: [COMMITTERS] pgsql: Add new replication mode synchronous_commit = 'write'. |