On Mon, 2010-08-30 at 09:59 +0300, Heikki Linnakangas wrote: > On 27/08/10 20:17, Fujii Masao wrote: > > Yes. StartupXLOG calls that before bgwriter is invoked. That is, we can > > ensure that StartupSUBTRANS has always been done before bgwriter > > performs a restartpoint. > > Hmm, the comment in CreateCheckpoint() isn't totally accurate either: > > > * Truncate pg_subtrans if possible. We can throw away all data before > > * the oldest XMIN of any running transaction. No future transaction > > will > > * attempt to reference any pg_subtrans entry older than that (see Asserts > > * in subtrans.c). During recovery, though, we mustn't do this because > > * StartupSUBTRANS hasn't been called yet.
Yep. > because in Hot Standby mode, StartSUBTRANS has been called already. We > could truncate pg_subtrans there too when hot standby is enabled. But > this is only about the startup checkpoint at the end of recovery, so I'm > inclined to not change that, not right now just before release anyway, > just in case we're missing something... > > However, is it safe to use GetOldestXMin() during recovery? Or to put it > other way, is GetOldestXMin() functioning correctly during hot standby? > It only scans through the ProcArray, but not the known-assigned xids > array. That seems like an oversight that needs to be fixed. Yes, thats correct. Otherwise the patch is fine. I'm working on this now and will commit something shortly. -- Simon Riggs www.2ndQuadrant.com PostgreSQL Development, 24x7 Support, Training and Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
