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

On Thu, Mar 3, 2022 at 4:22 PM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
> Following up on this now (will follow up on the "harden pruning" patch
> separately).

Attached is a new revision of my fix. This is more or less a
combination of my v4 fix from November 12 [1] and Andres'
already-committed fix (commit 18b87b20), rebased on top of HEAD. This
patch was originally a bugfix, but now it's technically just
refactoring/hardening of the logic in pruneheap.c. It hasn't changed
all that much, though.

We're still doing an up-front scan of the heap page to precalculate
HTSV for each tuple (no change from commit 18b87b20), but we no longer
do that on correctness grounds. It is purely a performance thing now.
Note that I am making a working assumption that that still makes sense
for now (I think that it probably does, but I haven't yet verified it
for myself).

We now do "3 passes" over the page. The first is the aforementioned
"precalculate HTSV" pass, the second is for determining the extent of
HOT chains, and the third is for any remaining disconnected/orphaned
HOT chains. I suppose that that's okay, since the amount of work has
hardly increased in proportion to this "extra pass over the page". Not
100% sure about everything myself right now, though. I guess that "3
passes" might be considered excessive.

[1] https://postgr.es/m/CAH2-WzmNk6V6tqzuuabxoxM8HJRaWU6h12toaS-bqYcLiht16A@mail.gmail.com
--
Peter Geoghegan