Thread: pgsql: Temporarily (I hope) disable flattening of IN/EXISTS sublinks
pgsql: Temporarily (I hope) disable flattening of IN/EXISTS sublinks
From
tgl@postgresql.org (Tom Lane)
Date:
Log Message:
-----------
Temporarily (I hope) disable flattening of IN/EXISTS sublinks that are within
the ON clause of an outer join. Doing so is semantically correct but results
in de-optimizing queries that were structured to take advantage of the sublink
style of execution, as seen in recent complaint from Kevin Grittner. Since
the user can get the other behavior by reorganizing his query, having the
flattening happen automatically is just a convenience, and that doesn't
justify breaking existing applications. Eventually it would be nice to
re-enable this, but that seems to require a significantly different approach
to outer joins in the executor.
Modified Files:
--------------
pgsql/src/backend/optimizer/prep:
prepjointree.c (r1.63 -> r1.64)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/prep/prepjointree.c?r1=1.63&r2=1.64)
Tom, you mentioned this should be a TODO item. Do we put it on our main TODO, and if so, in what section? --------------------------------------------------------------------------- Tom Lane wrote: > Log Message: > ----------- > Temporarily (I hope) disable flattening of IN/EXISTS sublinks that are within > the ON clause of an outer join. Doing so is semantically correct but results > in de-optimizing queries that were structured to take advantage of the sublink > style of execution, as seen in recent complaint from Kevin Grittner. Since > the user can get the other behavior by reorganizing his query, having the > flattening happen automatically is just a convenience, and that doesn't > justify breaking existing applications. Eventually it would be nice to > re-enable this, but that seems to require a significantly different approach > to outer joins in the executor. > > Modified Files: > -------------- > pgsql/src/backend/optimizer/prep: > prepjointree.c (r1.63 -> r1.64) > (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/prep/prepjointree.c?r1=1.63&r2=1.64) > > -- > Sent via pgsql-committers mailing list (pgsql-committers@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-committers -- Bruce Momjian <bruce@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + If your life is a hard drive, Christ can be your backup. +