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From: Tom Lane <[email protected]>
To: Tomas Vondra <[email protected]>
Cc: Jelte Fennema-Nio <[email protected]>
Cc: PostgreSQL-development <[email protected]>
Cc: Andres Freund <[email protected]>
Subject: Re: Bump soft open file limit (RLIMIT_NOFILE) to hard limit on startup
Date: Tue, 11 Feb 2025 18:04:15 -0500
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <CAGECzQQh6VSy3KG4pN1d=h9J=D1rStFCMR+t7yh_Kwj-g87aLQ@mail.gmail.com>
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Tomas Vondra <[email protected]> writes:
> On 2/11/25 21:18, Tom Lane wrote:
>> I think what we actually would like to know is how often we have to
>> close an open FD in order to make room to open a different file.
>> Maybe that's the same thing you mean by "cache miss", but it doesn't
>> seem like quite the right terminology.  Anyway, +1 for adding some way
>> to discover how often that's happening.

> We can count the evictions (i.e. closing a file so that we can open a
> new one) too, but AFAICS that's about the same as counting "misses"
> (opening a file after not finding it in the cache). After the cache
> warms up, those counts should be about the same, I think.

Umm ... only if the set of files you want access to is quite static,
which doesn't seem like a great bet in the presence of temporary
tables and such.  I think if we don't explicitly count evictions
then we'll be presenting misleading results.

			regards, tom lane

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