On Wed, Jun 4, 2014 at 9:56 AM, Andres Freund <and...@2ndquadrant.com> wrote: > On 2014-06-04 09:51:36 -0400, Robert Haas wrote: >> On Wed, Jun 4, 2014 at 2:08 AM, Andres Freund <and...@2ndquadrant.com> wrote: >> > On 2014-06-04 10:24:13 +0530, Amit Kapila wrote: >> >> Incase of recovery, the shared buffers saved by this utility are >> >> from previous shutdown which doesn't seem to be of more use >> >> than buffers loaded by recovery. >> > >> > Why? The server might have been queried if it's a hot standby one? >> >> I think that's essentially the same point Amit is making. Gurjeet is >> arguing for reloading the buffers from the previous shutdown at end of >> recovery; IIUC, Amit, you, and I all think this isn't a good idea. > > I think I am actually arguing for Gurjeet's position. If the server is > actively being queried (i.e. hot_standby=on and actually used for > queries) it's quite reasonable to expect that shared_buffers has lots of > content that is *not* determined by WAL replay. > > There's not that much read IO going on during WAL replay anyway - after > a crash/start from a restartpoint most of it is loaded via full page > anyway. So it's only disadvantageous to fault in pages via pg_hibernate > if that causes pages that already have been read in via FPIs to be > thrown out.
The thing I was concerned about is that the system might have been in recovery for months. What was hot at the time the base backup was taken seems like a poor guide to what will be hot at the time of promotion. Consider a history table, for example: the pages at the end, which have just been written, are much more likely to be useful than anything earlier. -- 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
