Horton

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

Peter Geoghegan <pg@bowt.ie>

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From: Peter Geoghegan <pg@bowt.ie>
To: Andres Freund <andres@anarazel.de>
Cc: Dmitry Dolgov <9erthalion6@gmail.com>, Alexander Lakhin <exclusion@gmail.com>, Matthias van de Meent <boekewurm+postgres@gmail.com>, PostgreSQL mailing lists <pgsql-bugs@lists.postgresql.org>
Date: 2022-03-11T04:55:37Z
Lists: pgsql-bugs 
On Thu, Mar 10, 2022 at 8:08 PM Andres Freund <andres@anarazel.de> wrote:
> But that's probably best done separately - but perhaps worth to "weaken" the
> comment a bit?

I'm confused again.

I don't get why it's only going to be worth delaying establishing
vistest if we can also delay establishing OldestXmin in about the same
way. AFAICT the only compelling reason to have two separate cutoffs
from the point of view of vacuumlazy.c is that it enables periodically
refreshing vistest within lazy_scan_prune, to allow it to prune dead
tuples more eagerly (fewer recently dead tuples, more dead removed
tuples). That I can see, that much I get.

Periodically refreshing OldestXmin for freezing won't work, though. At
the very least it seems much less compelling than the vistest idea.
Yes, it probably is true that we could in principle further split
OldestXmin along "xmin vs xid horizon" lines (I should say "split it
again" -- you already split OldestXmin into "OldestXmin for freezing,
vistest for pruning" as part of your snapshot scalability work). But
would it really make any sense? If so, I can't see why. At least not
right now.

--
Peter Geoghegan

Commits

  1. vacuumlazy.c: Standardize rel_pages terminology.

  2. vacuumlazy.c: document vistest and OldestXmin.

  3. heap pruning: Only call BufferGetBlockNumber() once.

  4. Fix possible HOT corruption when RECENTLY_DEAD changes to DEAD while pruning.

  5. Assert redirect pointers are sensible after heap_page_prune().

  6. Remove tupgone special case from vacuumlazy.c.

  7. Recycle nbtree pages deleted during same VACUUM.

  8. snapshot scalability: Don't compute global horizons while building snapshots.

  9. Refactor heap_page_prune so that instead of changing item states on-the-fly,