Re: Rework the way multixact truncations work

Noah, Robert, All

On 2015-12-11 11:20:21 -0500, Robert Haas wrote:
> On Thu, Dec 10, 2015 at 9:32 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> >> Adding a 'prevOffsetStopLimit' and using it seems like a ~5 line patch.
> >
> > So let's do that, then.
>
> Who is going to take care of this?

Here's two patches:

1) The fix to SetOffsetVacuumLimit().

I've tested this by introducing a probabilistic "return false;" to
find_multixact_start(), and torturing postgres by burning through
billions of multixactids of various sizes. Behaves about as
bad^Wgood as without the induced failures; before the patch there
were moments of spurious warnings/errors when ->offsetStopLimit was
out of whack.

2) A subset of the comment changes from Noah's repository. Some of the
comment changes didn't make sense without the removal
SlruScanDirCbFindEarliest(), a small number of other changes I couldn't
fully agree with.

Noah, are you ok with pushing that subset of your changes? Is
"Slightly edited subset of a larger patchset by Noah Misch" an OK
attribution?

Noah, on a first glance I think e50cca0ae ("Remove the
SlruScanDirCbFindEarliest() test from TruncateMultiXact().") is a good
idea. So I do encourage you to submit that as a separate patch.

Regards,

Andres