Re: Patch for fail-back without fresh backup

On 2013-06-14 09:21:52 -0400, Tom Lane wrote:
> Heikki Linnakangas <hlinnakangas@vmware.com> writes:
> > On 14.06.2013 16:08, Tom Lane wrote:
> >> Refresh my memory as to why we need to WAL-log hints for checksumming?
> 
> > Torn pages:
> 
> So it's not that we actually need to log the individual hint bit
> changes, it's that we need to WAL-log a full page image on the first
> update after a checkpoint, so as to recover from torn-page cases.
> Which one are we doing?

MarkBufferDirtyHint() loggs an FPI (just not via a BKP block) via
XLogSaveBufferForHint() iff XLogCheckBuffer() says we need to by
comparing GetRedoRecPtr() with the page's lsn.
Otherwise we don't do anything besides marking the buffer dirty.

Greetings,

Andres Freund

-- Andres Freund                       http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
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