On Wed, Aug 24, 2016 at 11:52 PM, Andres Freund <and...@anarazel.de> wrote: > On 2016-08-24 23:26:51 -0400, Robert Haas wrote: >> On Wed, Aug 24, 2016 at 10:54 PM, Andres Freund <and...@anarazel.de> wrote: >> > and I'm also rather doubtful that it's actually without overhead. >> >> Really? Where do you think the overhead would come from? > > ATM we do a math involving XLOG_BLCKSZ in a bunch of places (including > doing a lot of %). Some of that happens with exclusive lwlocks held, and > some even with a spinlock held IIRC. Making that variable won't be > free. Whether it's actually measurabel - hard to say. I do remember > Heikki fighting hard to simplify some parts of the critical code during > xlog scalability stuff, and that that even involved moving minor amounts > of math out of critical sections.
OK, that's helpful context. >> What sort of test would you run to try to detect it? > > Xlog scalability tests (parallel copy, parallel inserts...), and > decoding speed (pg_xlogdump --stats?) Thanks; that's helpful, too. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
