Re: HOT patch - version 15

On Mon, 2007-09-10 at 22:24 -0400, Tom Lane wrote:
> Simon Riggs <simon@2ndquadrant.com> writes:
> > On Tue, 2007-09-11 at 01:22 +0530, Pavan Deolasee wrote:
> >> I think the only difference is that the quick pruning does not mark
> >> intermediate tuples ~LP_USED and hence we may avoid WAL logging.
>
> > Sounds great.
>
> What it sounds is utterly unsafe.  You can get away with not WAL-logging
> individual bit flips (that is, hint-bit-setting) because either state of
> the page is valid.  If I read this proposal correctly it is to change
> t_ctid without WAL-logging, which means that a partial page write (torn
> page syndrome) could leave the page undetectably corrupted --- t_ctid
> is 6 bytes and could easily cross a hardware sector boundary.

We can calculate where they are, if thats the objection.

--
  Simon Riggs
  2ndQuadrant  http://www.2ndQuadrant.com