Re: [COMMITTERS] pgsql: Introduce WAL records to log reuse of btree pages, allowing

On Thu, 2010-02-18 at 14:23 +0200, Heikki Linnakangas wrote:
> Simon Riggs wrote:
> > Introduce WAL records to log reuse of btree pages, allowing conflict
> > resolution during Hot Standby. Page reuse interlock requested by Tom.
> > Analysis and patch by me.
> 
> There's still a theoretical possibility for this to happen:
> 
> 1. A page is marked as deleted by VACUUM, setting xact field in the opaque
> 2. Master crashes. WAL replay replays the XLOG_BTREE_DELETE_PAGE record.
> It resets the xact field to FrozenTransactionId
> 3. The page is recycled. This writes a XLOG_BTREE_REUSE_PAGE record with
> FrozenTransactionId as latestRemovedXid
> 
> When the standby replays that, it will call
> ResolveRecoveryConflictWithSnapshot with FrozenTransactionid, not the
> original xid that was used in the master when the page was deleted.
> 
> A straightforward way to fix that is to WAL-log the real xid in the
> XLOG_BTREE_DELETE_PAGE records, instead of resetting it to
> FrozenTransactionId.

Bug accepted, proposal implemented and committed.

-- Simon Riggs           www.2ndQuadrant.com