From: | Peter Geoghegan <pg(at)bowt(dot)ie> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Klaudie Willis <Klaudie(dot)Willis(at)protonmail(dot)com>, PostgreSQL mailing lists <pgsql-bugs(at)lists(dot)postgresql(dot)org> |
Subject: | Re: When Update balloons memory |
Date: | 2021-12-15 00:02:23 |
Message-ID: | CAH2-WzmhSUF6wLG5C3x__CPdX=9ec_Ou6Vkbpj7wZBJn2gsxMw@mail.gmail.com |
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On Tue, Dec 14, 2021 at 3:28 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Uh ... it seems that you are writing as though "giving the hint"
> means saying that the column value changed. That seems quite
> confusingly backwards to me, as that is/ought to be the expected
> assumption.
That's not what I meant. When I say "give the hint", I mean pass
"indexUnchanged = true" to aminsert(). This is interpreted within
btinsert() as "the incoming index tuple is a duplicate of at least one
index, so perform a bottom-up index deletion pass if and when the
alternative is splitting the leaf page". In practice the hint always
has to be treated as a noisy signal about what might work, as a
strategy of last resort, with costs that are imposed on non-HOT
updaters.
--
Peter Geoghegan
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