Re: corrupt pages detected by enabling checksums

On Mon, 2013-04-08 at 09:19 +0100, Simon Riggs wrote:

> Applied, with this as the only code change.
>
>
> Thanks everybody for good research and coding and fast testing.
>
>
> We're in good shape now.

Thank you.

I have attached two more patches:

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.

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.

Regards,
    Jeff Davis