[PERFORM] Can improve 'limit 1' ? with slow function
The simplified scene:
select slowfunction() from a order by b limit 1
is slow than
select slowfunction() from ( select * from a order by b limit 1)
if there are many records in table 'a'
The real scene:
function ST_Distance_Sphere is slow than ST_Distance, the query:
SELECT ST_Distance_Sphere(s, ST_GeomFromText('POINT(1 1)')) from road order by
ST_Distance(s, ST_GeomFromText('POINT(1 1)')) limit 1
is slow than:
select ST_Distance_Sphere(s, ST_GeomFromText('POINT(1 1)')) from (SELECT s from
road order by ST_Distance(s, ST_GeomFromText('POINT(1 1)')) limit 1) as a
There are about 7000 records in 'road'.
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Re: [PERFORM] 60 core performance with 9.3
On 2014-06-27 14:28:20 +1200, Mark Kirkwood wrote: My feeling is spinlock or similar, 'perf top' shows kernel find_busiest_group kernel _raw_spin_lock as the top time users. Those don't tell that much by themselves, could you do a hierarchical profile? I.e. perf record -ga? That'll at least give the callers for kernel level stuff. For more information compile postgres with -fno-omit-frame-pointer. Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training Services -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] 60 core performance with 9.3
On 27/06/14 21:19, Andres Freund wrote: On 2014-06-27 14:28:20 +1200, Mark Kirkwood wrote: My feeling is spinlock or similar, 'perf top' shows kernel find_busiest_group kernel _raw_spin_lock as the top time users. Those don't tell that much by themselves, could you do a hierarchical profile? I.e. perf record -ga? That'll at least give the callers for kernel level stuff. For more information compile postgres with -fno-omit-frame-pointer. Excellent suggestion, will do next week! regards Mark -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
