On Fri, 21 Dec 2018 at 06:44, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> I was distressed to discover via perf that 69% of the runtime of this
> test now goes into match_eclasses_to_foreign_key_col(). That seems
> clearly unacceptable.
Agreed. That's pretty terrible.
I looked at this a bit and see that
match_eclasses_to_foreign_key_col() is missing any smarts to skip
equivalence classes that don't have ec_relids bits for both rels. With
that added the run-time is reduced pretty dramatically.
I've only tested with a debug build as of now, but I get:
Unpatched:
$ pgbench -n -T 60 -f query.sql postgres
latency average = 18411.604 ms
Patched:
latency average = 8748.177 ms
Going by my profiler this drops match_eclasses_to_foreign_key_col()
down to just 10% of total planner time for this query. The new
bms_is_member() call is pretty hot inside that function though.
--
David Rowley http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
