On Thu, 2010-04-29 at 13:01 -0500, Kevin Grittner wrote: > Simon Riggs <si...@2ndquadrant.com> wrote: > > > I've asked for evidence that recovery is any slower as a result of > > HS. > > Can you quantify the impact on the number of bytes written to WAL > when switching from the archiving level to the hot standby level?
Sure, done that a few times. Extra WAL data is written for these actions, listed in order of increasing size * commit records contain a variable length list of relcacheinvalidations, mostly applies only to DDL * one extra WAL record in most VACUUMs, fairly small, optimised away in some cases * a transaction issues more than 64 subtransactions it will issue a record approx 256 bytes plus header * one extra WAL record every checkpoint, containing a full current snapshot's worth of running xids 100-400 bytes typically, could go up from there to 4000 bytes in very extreme write workloads that also have many, many subtransactions -- Simon Riggs www.2ndQuadrant.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
