Thomas Munro wrote: > My idea was that if I could get oldestXact == next XID in > TruncateSUBSTRANS, then TransactionIdToPage(oldestXact) for a value of > oldestXact that happens to be immediately after a page boundary (so > that xid % 2048 == 0) might give page number that is >= > latest_page_number, causing SimpleLruTruncate to print that message. > But I can't figure out how to get next XID == oldest XID, because > vacuumdb --freeze --all consumes xids itself, so in my first attempt > at this, next XID is always 3 ahead of the oldest XID when a > checkpoint is run.
vacuumdb starts by querying pg_database, which eats one XID. Vacuum itself only uses one XID when vac_truncate_clog() is called. This is called from vac_update_datfrozenxid(), which always happen at the end of each user-invoked VACUUM (so three times for vacuumdb if you have three databases); autovacuum does it also at the end of each run. Maybe you can get autovacuum to quit before doing it. OTOH, if the values in the pg_database entry do not change, vac_truncate_clog is not called, and thus vacuum would finish without consuming an XID. -- Álvaro Herrera http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, 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
