From: | David Rowley <dgrowleyml(at)gmail(dot)com> |
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To: | Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com> |
Cc: | Ahmed Yarub Hani Al Nuaimi <ahmedyarubhani(at)gmail(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Lock-free compaction. Why not? |
Date: | 2024-07-18 11:07:54 |
Message-ID: | CAApHDvrO6H+dCO1CyEHaDC3TerWrkHs-dd7g8af5VDHALyUZVQ@mail.gmail.com |
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On Wed, 10 Jul 2024 at 22:58, Tomas Vondra
<tomas(dot)vondra(at)enterprisedb(dot)com> wrote:
> IIRC long time ago VACUUM FULL actually worked in a similar way, i.e. by
> moving rows around. I'm not sure if it did the lock-free thing as
> proposed here (probably not), but I guess at least some of the reasons
> why it was replaced by CLUSTER would still apply to this new thing.
Yeah, that changed in 9.0. The old version still obtained an AEL on the table.
I think the primary issue with the old way was index bloat wasn't
fixed. The release notes for 9.0 do claim the CLUSTER method "is
substantially faster in most cases", however, I imagine there are
plenty of cases where it wouldn't be. e.g, it's hard to imagine
rewriting the entire 1TB table and indexes is cheaper than moving 1
row out of place row.
David
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