On Sun, Oct 16, 2016 at 3:35 PM, Jeff Janes <jeff.ja...@gmail.com> wrote: > On Fri, Oct 7, 2016 at 6:14 AM, Robert Haas <robertmh...@gmail.com> wrote: >> On Thu, Oct 6, 2016 at 8:40 PM, Jeff Janes <jeff.ja...@gmail.com> wrote: >> > In commit 37484ad2aacef5ec7, you changed the way that frozen tuples were >> > represented, so that we could make freezing more aggressive without >> > losing >> > forensic evidence. But I don't think we ever did anything to actually >> > make >> > the freezing more aggressive. >> >> See 3cff1879f8d03cb729368722ca823a4bf74c0cac. The objection to doing >> it in other cases is that it adds write-ahead log volume which might >> cause its own share of problems. There might be some way of getting >> ahead of that, though. I think if we piggyback on an existing WAL >> record like XLOG_HEAP2_CLEAN or XLOG_HEAP2_VISIBLE the impact might be >> minimal, but I haven't been dedicated enough to try to write the >> patch. >> >> > When I applied the up-thread patch so that pgbench_history gets autovac, >> > those autovacs don't actually cause any pages to get frozen until the >> > wrap >> > around kicks in, even when all the tuples on the early pages should be >> > well >> > beyond vacuum_freeze_min_age. >> >> If the pages are already all-visible, they'll be skipped until >> vacuum_freeze_table_age is reached. > > So if I set vacuum_freeze_min_age to zero, then they should become > all-visible and all-frozen at the same time, and avoid that problem?
Hmm. I *think* so... > From the docs on vacuum_freeze_min_age: "Increasing this setting may avoid > unnecessary work if the rows that would otherwise be frozen will soon be > modified again". How much work is that? Presumably they are already getting > marked visible, is marking them frozen too a meaningful amount of extra > work? Is it just the extra WAL record? Yeah, the extra WAL record is the main thing, I think. -- 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
