On Mon, 2006-10-30 at 19:18 -0500, Tom Lane wrote: > "Simon Riggs" <[EMAIL PROTECTED]> writes: > > I don't agree: If the truncation points are at 1 million, 2 million etc, > > then if we advance the relvacuumxid from 1.2 million to 1.5 million, > > then crash, the hints bits for that last vacuum are lost. Sounds bad, > > but we have not truncated clog, so there is no danger. > > You're still wrong though.
Frequently, I'd say :-) > Suppose that VACUUM moves a particular rel's > relvacuumxid from 1.9 to 2.1 million, but because this rel is not > currently the oldest vacuumxid, it doesn't truncate clog. Then we crash > and lose hint bits, but not the relvacuumxid change. Then VACUUM > vacuums some other rel and advances its relvacuumxid from 1.9 to 2.1 > million --- but this time that *was* the globally oldest value, and now > we think we can truncate clog at 2 million. But the first rel might > still have some unhinted xids around 1.9 million. That was understood; in the above example I agree you need to flush. If you don't pass a truncation point, you don't need to flush whether or not you actually truncate. So we don't need to flush *every* time, so IMHO we don't need to play safe and keep clog the size of an iceberg. Anyway, if PITR is safe again, I'd like to sleep....zzzzzzzzzzzzzz -- Simon Riggs EnterpriseDB http://www.enterprisedb.com ---------------------------(end of broadcast)--------------------------- TIP 5: don't forget to increase your free space map settings
