On 31 July 2014 07:45, Michael Paquier <michael.paqu...@gmail.com> wrote:

>> So I don't see the need for two full page images.

> By doing so you definitely need an additional mode for full-page
> writes: one certifying that process does not apply this FPW because it
> wants to compare it to current page after applying the WALs. This
> increases the footprint of the feature on code because all the code
> paths where RestoreBackupBlock is called need to be bypassed.

Yeh, it looks like you need to do CheckBackupBlock() exactly as many
times as you do RestoreBackupBlock(), with the sequence of actions
being RestoreBackupBlock(), apply WAL then CheckBackupBlock(). That
will work without much code churn, it will be just a one line addition
in a few dozen places.

 Simon Riggs                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

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