On Sat, Feb 13, 2021 at 10:47 PM Peter Geoghegan <p...@bowt.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
v4-0002-Recycle-pages-deleted-during-same-VACUUM.patch
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v4-0001-Use-full-64-bit-XID-for-nbtree-page-deletion.patch
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v4-0003-Add-pages_newly_deleted-to-VACUUM-VERBOSE.patch
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