Alvaro Herrera <[EMAIL PROTECTED]> writes: > Tom Lane wrote: >> The proper interpretation of the pg_database columns >> is that we guarantee that all XID's in the database are *at least* thus- >> and-so, not that the minimum is exact.
> Ah-ha, an easier approach. This would mean either: > a) we need to seqscan pg_class each time to discover the minimum We'd have to do that during each VACUUM to see if we could change the pg_database entry, I think. > b) we need a partial index on pg_class (relminxid) WHERE relkind = 'r' > to quickly discover the minimum > (Is the bootstrap mode able to create partial indexes?) No, and we can't update them on system catalogs either, so it's not gonna work. (I think plain tables are a large enough fraction of pg_class that you'd not save anything anyway...) > We need to do this after each vacuum. > We could arrange things so that autovacuum manages to do it only once > after processing a database instead of once per table, but this could be > fragile if the vacuuming dies partway through. No, it'd just mean that the pg_database entry is smaller than it could be, but this is not a failure case. Note that a plain manual full-database VACUUM could have the same optimization; it's not only autovac. > This reminds me of an unrelated problem. On pgsql-bugs or > pgsql-es-ayuda there was a report recently that autovacuum was dying > because of corrupt data on a database. The problem was that this > prevented vacuuming of all other databases as well, because on the next > autovacuum iteration the same database would be chosen and the same > error would ensue. Probably we should do something about this, so that > autovac is allowed to process other databases before failing again on > the offending database. Hm, I kinda thought we had already got some provision in there to discourage autovac from choosing the same database over and over. regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 4: Have you searched our list archives? http://archives.postgresql.org