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

Andres Freund <andres@anarazel.de>

From: Andres Freund <andres@anarazel.de>

To: Dmitry Koterov <dmitry.koterov@gmail.com>

Cc: "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>

Date: 2025-02-01T15:50:37Z

Lists: pgsql-hackers

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Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

doc: Fix pg_buffercache_evict() title
- 59d6c0395619 18.0 cited
Fix several hash functions that were taking chintzy shortcuts instead of
- 1f559b7d3aa4 8.3.0 cited

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