Kevin Grittner wrote: >>>> On Thu, Oct 18, 2007 at 11:23 AM, in message > <[EMAIL PROTECTED]>, Gregory Stark <[EMAIL PROTECTED]> > wrote: > >> If it's set to 0 >> then there's no real reason we need to wal log lock operations. > > Do we currently take advantage of that fact, or log them anyway?
No, we log them anyway. There's a few other reasons to WAL log lock operations, see comments in heap_lock_tuple: > /* > * XLOG stuff. You might think that we don't need an XLOG record > because > * there is no state change worth restoring after a crash. You would be > * wrong however: we have just written either a TransactionId or a > * MultiXactId that may never have been seen on disk before, and we need > * to make sure that there are XLOG entries covering those ID numbers. > * Else the same IDs might be re-used after a crash, which would be > * disastrous if this page made it to disk before the crash. Essentially > * we have to enforce the WAL log-before-data rule even in this case. > * (Also, in a PITR log-shipping or 2PC environment, we have to have XLOG > * entries for everything anyway.) > */ There's also the risk of torn pages. We set the xmax and the XMAX_*_LOCK flag in heap_lock_tuple, and it's possible that only one of those changes is written to disk before crash. -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com ---------------------------(end of broadcast)--------------------------- TIP 7: You can help support the PostgreSQL project by donating at http://www.postgresql.org/about/donate
