Re: hash_search_with_hash_value is high in "perf top" on a replica

From: Andres Freund <andres(at)anarazel(dot)de>
To: Dmitry Koterov <dmitry(dot)koterov(at)gmail(dot)com>
Cc: "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: hash_search_with_hash_value is high in "perf top" on a replica
Date: 2025-02-01 15:50:37
Message-ID: 2oapols65vuwgp43bu5ikgb3om4jrh24dcs5wz2uo3qrugyvyh@bt2vho43nncq
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Hi,

On 2025-02-01 03:46:33 -0800, Dmitry Koterov wrote:
> > It'd be interesting to see what the paths towards
> hash_search_with_hash_value
> are.
>
> One of the popular paths is on the screenshot. They are all more or less
> the same when recovery_prefetch=on (and when it's off, the replica behaves
> worse, more replication lag).

Yea, I was hoping for a profile with recovery_prefetch=off, so we can see what
records are causing most of the "slow" lookups.

Greetings,

Andres Freund

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