Re: corrupt pages detected by enabling checksums

On 9 April 2013 08:36, Jeff Davis <pgsql@j-davis.com> wrote:

> 1. I believe that the issue I brought up at the end of this email:
>
> http://www.postgresql.org/message-id/1365035537.7580.380.camel@sussancws0025
>
> is a real issue. In lazy_vacuum_page(), the following sequence can
> happen when checksums are on:
>
>    a. PageSetAllVisible
>    b. Pass heap page to visibilitymap_set
>    c. visibilitymap_set logs the heap page and sets the LSN
>    d. MarkBufferDirty
>
> If a checkpoint happens between (c) and (d), then we have a problem. The
> fix is easy: just mark the heap buffer dirty first. There's another call
> site that looks like a potential problem, but I don't think it is. I
> simplified the code there to make it (hopefully) more clearly correct.


Applied

> 2. A cleanup patch to pass the buffer_std flag down through
> MarkBufferDirtyHint. This is a matter of preference and purely cosmetic,
> so it might not be wanted. The reason I thought it was useful is that a
> future caller that sets a hint on a non-standard buffer might easily
> miss the assumption that we have a standard buffer.

Skipped that for now. Do we really need it? Can you set a hint on a
non-standard buffer?

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