Re: Stats collector performance improvement
От | Hannu Krosing |
---|---|
Тема | Re: Stats collector performance improvement |
Дата | |
Msg-id | 1136238496.4256.9.camel@localhost.localdomain обсуждение исходный текст |
Ответ на | Re: Stats collector performance improvement (Tom Lane <tgl@sss.pgh.pa.us>) |
Список | pgsql-hackers |
Ühel kenal päeval, E, 2006-01-02 kell 15:20, kirjutas Tom Lane: > [ moving to -hackers ] > > Bruce Momjian <pgman@candle.pha.pa.us> writes: > > I did some research on this because the numbers Tom quotes indicate there > > is something wrong in the way we process stats_command_string > > statistics. > > [ ... proposed patch that seems pretty klugy to me ... ] > > I wonder whether we shouldn't consider something more drastic, like > getting rid of the intermediate stats buffer process entirely. > > The original design for the stats communication code was based on the > premise that it's better to drop data than to make backends wait on > the stats collector. However, as things have turned out I think this > notion is a flop: the people who are using stats at all want the stats > to be reliable. We've certainly seen plenty of gripes from people who > are unhappy that backend-exit messages got dropped, and anyone who's > using autovacuum would really like the tuple update counts to be pretty > solid too. > > If we abandoned the unreliable-communication approach, could we build > something with less overhead? Weell, at least it should be non-WAL, and probably non-fsync, at least optionally . Maybe also inserts inserts + offline aggregator (instead of updates) to avoid lock contention. Something that collects data in blocks of local or per-backend shared memory in each backend and then gives complete blocks to aggregator process. Maybe use 2 alternating blocks per backend - 1 for ongoing stats collection and another given to aggregator. this has a little time shift, but will deliver accurate starts in the end. Things that need up-to-date stats (like pg_stat_activity), should look (and lock) also the ongoing satas collection blocks if needed (how do we know know the *if*) and delay each backend process momentaryly by looking. ----------------- Hannu
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