Andres Freund wrote: > On 2014-05-15 15:40:06 -0400, Robert Haas wrote: > > On Thu, May 15, 2014 at 2:34 PM, Bruce Momjian <br...@momjian.us> wrote:
> > If the larger clog size is a show-stopper (and I'm not sure I have an > > intelligent opinion on that just yet), one way to get around the > > problem would be to summarize CLOG entries after-the-fact. Once an > > XID precedes the xmin of every snapshot, we don't need to know the > > commit LSN any more. So we could read the old pg_clog files and write > > new summary files. Since we don't need to care about subcommitted > > transactions either, we could get by with just 1 bit per transaction, > > 1 = committed, 0 = aborted. Once we've written and fsync'd the > > summary files, we could throw away the original files. That might > > leave us with a smaller pg_clog than what we have today. > > I think the easiest way for now would be to have pg_clog with the same > format as today and a rangewise much smaller pg_csn storing the lsns > that are needed. That'll leave us with pg_upgrade'ability without > needing to rewrite pg_clog during the upgrade. Err, we're proposing a patch to add timestamps to each commit, http://www.postgresql.org/message-id/20131022221600.ge4...@eldon.alvh.no-ip.org which does so in precisely this way. The idea that pg_csn or pg_committs can be truncated much earlier than pg_clog has its merit, no doubt. If we can make sure that the atomicity is sane, +1 from me. -- Álvaro Herrera 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
