Thread: Re: [COMMITTERS] pgsql: Reset btpo.xact following recovery of btree delete page.

sriggs@postgresql.org (Simon Riggs) writes:
> Log Message:
> -----------
> Reset btpo.xact following recovery of btree delete page. Add btpo_xact
> field into WAL record and reset it from there, rather than using
> FrozenTransactionId which can lead to some corner case bugs.

Simon, you can't just whack WAL record contents around without a care.
This commit breaks on-disk WAL compatibility and will result in possibly
unrecoverable databases as soon as someone applies it; not to mention
what will happen if an HS slave is not running the same code as its
master.  This must be treated as an initdb-forcing, or at least
pg_resetxlog-forcing, change.

The correct thing to do when committing such a change is to change the
WAL-file magic number XLOG_PAGE_MAGIC.
        regards, tom lane

On Fri, 2010-03-19 at 08:41 -0400, Tom Lane wrote:
> sriggs@postgresql.org (Simon Riggs) writes:
> > Log Message:
> > -----------
> > Reset btpo.xact following recovery of btree delete page. Add btpo_xact
> > field into WAL record and reset it from there, rather than using
> > FrozenTransactionId which can lead to some corner case bugs.
> 
> Simon, you can't just whack WAL record contents around without a care.
> This commit breaks on-disk WAL compatibility and will result in possibly
> unrecoverable databases as soon as someone applies it; not to mention
> what will happen if an HS slave is not running the same code as its
> master.  This must be treated as an initdb-forcing, or at least
> pg_resetxlog-forcing, change.

OK, understood. 

> The correct thing to do when committing such a change is to change the
> WAL-file magic number XLOG_PAGE_MAGIC.

Will do

-- Simon Riggs           www.2ndQuadrant.com