Attached is a draft patch for the WAL-and-freezing issues we've been discussing. This incorporates Heikki and Simon's work on providing WAL-logging for tuple freezing actions and pg_clog truncation respectively, and adds on several other things:
* replace logic for when to truncate pg_clog, as discussed: it's now driven off the system-wide minimum relfrozenxid. * add GUC variables and pg_autovacuum support to control the freeze distance (how far back a VACUUM sets its freeze cutoff, which becomes the table's new relfrozenxid) as well as the freeze limit (the age of relfrozenxid at which we force an autovacuum cycle). * revise the autovacuum logic to exploit the per-table tracking of relfrozenxid better: there is no concept of a "database wide autovacuum" anymore, rather we make table-by-table decisions about what needs to be vacuumed. * revise the mechanism for forcing autovacs when the freeze limit is exceeded --- this was previously checked only on completion of a VACUUM, which seems a bit untrustworthy (if you're not vacuuming, it won't help). I moved the functionality to varsup.c instead, where we already had the forced-shutdown-before-wraparound code. The patch is not ready to apply because it needs more testing (anyone want to help?) and because I need to do more documentation work; maintenance.sgml and the vacuum ref page both need some TLC. Comments? regards, tom lane
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Description: wal-freezing.patch.gz
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