From: | Peter Geoghegan <pg(at)bowt(dot)ie> |
---|---|
To: | Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> |
Cc: | PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi> |
Subject: | Re: 64-bit XIDs in deleted nbtree pages |
Date: | 2021-02-15 04:39:53 |
Message-ID: | CAH2-WznqkSRauaqZ9x88hHVDq=8JvxB7=t7iucZTbS61xg32Fw@mail.gmail.com |
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Lists: | pgsql-hackers |
On Sat, Feb 13, 2021 at 10:47 PM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
> It will be rare. But more importantly, the fact that scenario is now
> an extreme case justifies treating it as an extreme case. We can teach
> _bt_vacuum_needs_cleanup() to recognize it as an extreme case, too. In
> particular, I think that it will now be okay to increase the threshold
> applied when considering deleted pages inside
> _bt_vacuum_needs_cleanup(). It was 2.5% of the index size in v3 of the
> patch. But in v4, which has the new recycling enhancement, I think
> that it would be sensible to make it 5%, or maybe even 10%. This
> naturally makes Masahiko's problem scenario unlikely to actually
> result in a truly wasted call to btvacuumscan().
Attached is v4, which has the "recycle pages that we ourselves deleted
during this same VACUUM operation" enhancement. It also doubles the
_bt_vacuum_needs_cleanup() threshold applied to deleted pages -- it
goes from 2.5% to 5%. The new patch is the patch series (v4-0002-*)
certainly needs more polishing. I'm posting what I have now because v3
has bitrot.
Benchmarking has shown that the enhancement in v4-0002-* can
significantly reduce the amount of index bloat in two of the
BenchmarkSQL/TPC-C indexes.
--
Peter Geoghegan
Attachment | Content-Type | Size |
---|---|---|
v4-0002-Recycle-pages-deleted-during-same-VACUUM.patch | application/octet-stream | 11.4 KB |
v4-0001-Use-full-64-bit-XID-for-nbtree-page-deletion.patch | application/octet-stream | 74.1 KB |
v4-0003-Add-pages_newly_deleted-to-VACUUM-VERBOSE.patch | application/octet-stream | 7.2 KB |
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