Re: BUG #17255: Server crashes in index_delete_sort_cmp() due to race condition with vacuum

Hi,

On 2022-03-10 19:52:24 -0800, Peter Geoghegan wrote:
> As the patch points out, we are required to establish rel_pages after
> we have established OldestXmin.

Hm. Now that I think more about it, I'm not as convinced that's entirely true
anymore. We just need to make sure that we have an accurate "xid horizon" from
before determining the relation size, not an "xmin horizon" and use the Min()
of the two horizons.  The "xid horizon" obviously is typically well ahead of
the "xmin horizon" (and always >=).

And even on the "xid horizon" I suspect something more aggressive could be
used.

But that's probably best done separately - but perhaps worth to "weaken" the
comment a bit?

Greetings,

Andres Freund