postgresql/contrib/citext
Tom Lane 9c7f5229ad Optimize joins when the inner relation can be proven unique.
If there can certainly be no more than one matching inner row for a given
outer row, then the executor can move on to the next outer row as soon as
it's found one match; there's no need to continue scanning the inner
relation for this outer row.  This saves useless scanning in nestloop
and hash joins.  In merge joins, it offers the opportunity to skip
mark/restore processing, because we know we have not advanced past the
first possible match for the next outer row.

Of course, the devil is in the details: the proof of uniqueness must
depend only on joinquals (not otherquals), and if we want to skip
mergejoin mark/restore then it must depend only on merge clauses.
To avoid adding more planning overhead than absolutely necessary,
the present patch errs in the conservative direction: there are cases
where inner_unique or skip_mark_restore processing could be used, but
it will not do so because it's not sure that the uniqueness proof
depended only on "safe" clauses.  This could be improved later.

David Rowley, reviewed and rather heavily editorialized on by me

Discussion: https://postgr.es/m/CAApHDvqF6Sw-TK98bW48TdtFJ+3a7D2mFyZ7++=D-RyPsL76gw@mail.gmail.com
2017-04-07 22:20:13 -04:00
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expected Optimize joins when the inner relation can be proven unique. 2017-04-07 22:20:13 -04:00
sql Test all contrib-created operator classes with amvalidate. 2016-11-29 15:05:22 -05:00
.gitignore
citext--1.0--1.1.sql Fix incorrect declaration of citext's regexp_matches() functions. 2015-05-05 15:51:22 -04:00
citext--1.1--1.2.sql Schema-qualify some references to regprocedure. 2016-06-10 10:41:58 -04:00
citext--1.2--1.3.sql Repair damage done by citext--1.1--1.2.sql. 2016-07-26 15:32:57 -04:00
citext--1.3--1.4.sql Support the new regexp_match() function for citext. 2016-08-18 10:52:31 -04:00
citext--1.4.sql Support the new regexp_match() function for citext. 2016-08-18 10:52:31 -04:00
citext--unpackaged--1.0.sql Fix citext upgrade script for disallowance of oidvector element assignment. 2014-08-28 18:21:05 -04:00
citext.c Move some things from builtins.h to new header files 2017-01-20 20:29:53 -05:00
citext.control Support the new regexp_match() function for citext. 2016-08-18 10:52:31 -04:00
Makefile Support the new regexp_match() function for citext. 2016-08-18 10:52:31 -04:00