|From:||David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>|
|To:||Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>|
|Cc:||PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>|
|Subject:||Re: Performance issue in foreign-key-aware join estimation|
|Views:||Raw Message | Whole Thread | Download mbox|
On Fri, 21 Dec 2018 at 06:44, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)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:
$ pgbench -n -T 60 -f query.sql postgres
latency average = 18411.604 ms
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
|Next Message||David Fetter||2018-12-21 20:32:17||Re: Compiling on Termux|
|Previous Message||Michael Banck||2018-12-21 20:16:16||Offline enabling/disabling of data checksums|