On 2014-08-11 12:42:06 +0900, Fujii Masao wrote: > On Mon, Aug 11, 2014 at 10:48 AM, Tatsuo Ishii <is...@postgresql.org> wrote: > >> On Mon, Aug 11, 2014 at 9:23 AM, Tatsuo Ishii <is...@postgresql.org> wrote: > >>> We can know the LSN of last committed WAL record on primary by using > >>> pg_current_xlog_location(). It seems there's no API to know the time > >>> when the WAL record was created. I would like to know standby delay by > >>> using pg_last_xact_replay_timestamp() and such that API. > >>> > >>> If there's no such a API, it would be useful to invent usch an API IMO. > >> > >> +1 > >> > >> I proposed that function before, but unfortunately it failed to be applied. > >> But I still think that function is useful to calculate the replication > >> delay. > >> The past discussion is > >> http://www.postgresql.org/message-id/cahgqgwf3zjfunej5ka683ku5rqubtswtqfq7g1x0g34o+jx...@mail.gmail.com > > > > I looked into the thread briefly and found Simon and Robert gave -1 > > for this because of performance concern. I'm not sure if it's a actual > > performance penalty or not. Maybe we need to major the penalty? > > I think that the performance penalty is negligible small because the patch > I posted before added only three stores to shared memory per > commit/abort.
Uh. It adds another atomic operation (the spinlock) to the commit path. That's surely *not* insignificant. At the very least the concurrency approach needs to be rethought. Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
