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help / color / mirror / Atom feedFrom: Adrian Klaver <[email protected]>
To: Koen De Groote <[email protected]>
To: PostgreSQL General <[email protected]>
Subject: Re: On a subscriber, why is last_msg_send_time in pg_stat_subscription sometimes null?
Date: Fri, 23 Aug 2024 08:02:56 -0700
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAGbX52H8dDW8nVC8Zxg0-HFY58fAXd93XuxC83_DPHARZkpepw@mail.gmail.com>
References: <CAGbX52H8dDW8nVC8Zxg0-HFY58fAXd93XuxC83_DPHARZkpepw@mail.gmail.com>
On 8/23/24 07:33, Koen De Groote wrote:
> I'm running this query:
>
> SELECT subname, received_lsn, latest_end_lsn,
> last_msg_send_time, last_msg_receipt_time
> FROM pg_catalog.pg_stat_subscription;
>
> And "last_msg_send_time" will sometimes be null. All I can find in the
> documentation is that this value represents: "Send time of last message
> received from origin WAL sender; NULL for parallel apply workers"
>
> But I have no context for what parallel apply workers are or why they
> are NULL sometimes and other times not. >
> Can anyone explain?
The source has that information:
https://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=src/backend/replication/logical/applypa...
The top part explains the process.
As to the time:
/*
* There are three fields in each message received by the parallel apply
* worker: start_lsn, end_lsn and send_time. Because we have updated these
* statistics in the leader apply worker, we can ignore these fields in the
* parallel apply worker (see function LogicalRepApplyLoop).
*/
>
> Regards,
> Koen De Groote
--
Adrian Klaver
[email protected]
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