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From: Adrian Klaver <[email protected]>
To: Dominique Devienne <[email protected]>
To: Tom Lane <[email protected]>
Cc: [email protected]
Subject: Re: is pg_stat_activity "transactional"? How fast does it update?
Date: Tue, 10 Jun 2025 09:03:48 -0700
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAFCRh--LyhHAOYKWE+NDCN8cB4pGiO82p1Ye9pT9T7fv7i2BfA@mail.gmail.com>
References: <CAFCRh-8WDkn2N+s43fofR4eKHcJC8fiotqWqSGkDQ4Sh4ZYwDg@mail.gmail.com>
	<[email protected]>
	<CAFCRh--LyhHAOYKWE+NDCN8cB4pGiO82p1Ye9pT9T7fv7i2BfA@mail.gmail.com>

On 6/10/25 08:46, Dominique Devienne wrote:
> On Tue, Jun 10, 2025 at 4:27 PM Tom Lane <[email protected]> wrote:
>> Dominique Devienne <[email protected]> writes:
>>> So when and how fast does pg_stat_activity update, in the face of a
>>> PQfinish?
>>
>> The shared state underlying pg_stat_activity is updated
>> immediately when something changes.  However ...
>>
>> PQfinish is asynchronous: it sends a "goodbye" message and then
>> closes the connection without waiting for a response.  So
>> depending on system load, the associated backend could still be
>> alive for some milliseconds.  There might be other client
>> libraries that do that differently.
>>
>> Another thing that might be biting you is that a backend inspecting
>> pg_stat_activity() takes a snapshot of the view's contents and then
>> holds onto that snapshot until end of transaction.  You can get
>> around that with pg_stat_clear_snapshot().
> 
> Many thanks Tom. Didn't know either of those facts. --DD
> 

For more detail see:

https://www.postgresql.org/docs/current/monitoring-stats.html#MONITORING-STATS-VIEWS

-- 
Adrian Klaver
[email protected]

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