Обсуждение: PD_ALL_VISIBLE flag set - autovacuum ignoring dead tuples
I'm seeing a heavy-update TOAST table which is not being effectively autovacuum'd on 8.4.5. The stats collector shows n_dead_tupgrowing very quickly, and autovacuum runs frequently, but never removes any dead tuples. A manual vacuum doesfind many dead tuples (90+ % of the table) to remove, and removes them properly. Whilst debugging, I found that there seems to be a large amount of the old 'PD_ALL_VISIBLE incorrectly set...' warnings emittedduring the autovacuum run. My immediate assumption was that PD_ALL_VISIBLE is set on the page, and so autovacuum skips it. However, from what I cansee in lazy_scan_heap(), all of the clean-up actually happens before we even check the PD_ALL_VISIBLE flag and emit thiswarning. Can anyone confirm that this is a warning message only, and shouldn't actually cause autovacuum to skip pruningdead tuples? Am I seeing two different or related issues here? Thanks, Tom p.s. I'm aware there was a change to PD_ALL_VISIBLE in 8.4.8 but that was to stop warning on a non-issue, so I don't believeit's the same.
Tom Lanyon <tom+pgsql-admin@oneshoeco.com> writes: > I'm seeing a heavy-update TOAST table which is not being effectively autovacuum'd on 8.4.5. The stats collector showsn_dead_tup growing very quickly, and autovacuum runs frequently, but never removes any dead tuples. A manual vacuumdoes find many dead tuples (90+ % of the table) to remove, and removes them properly. Is autovacuum actually running against the toast table? Check the last_autovacuum column in pg_stat_all_tables. If not, and if pg_class' relpages/reltuples columns seem pretty out of date for the toast table, this might be a variant of the problem reported here: http://archives.postgresql.org/pgsql-admin/2011-05/msg00101.php which was patched here: http://git.postgresql.org/gitweb/?p=postgresql.git&a=commitdiff&h=b503da135ab0bdd97ac3d3f720c35854e084e525 although that patch hasn't actually made it into any shipping release yet :-( I'm not entirely convinced that you're seeing a related issue, because Florian was complaining of too many autovacuums not too few, but if you cross your eyes a bit and assume the symptom is "poor autovacuum scheduling" then maybe the same problem explains both. Another post-8.4.5 bug fix that could affect autovacuum's promptness is http://git.postgresql.org/gitweb/?p=postgresql.git&a=commitdiff&h=fab2af30d6bb4ca893e2e9bf96863e6f1ce826d2 > Whilst debugging, I found that there seems to be a large amount of the old 'PD_ALL_VISIBLE incorrectly set...' warningsemitted during the autovacuum run. If that were the issue, manual vacuums would be subject to it too. regards, tom lane