Re: Synchronizing slots from primary to standby

From: Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
To: Peter Smith <smithpb2250(at)gmail(dot)com>
Cc: "Zhijie Hou (Fujitsu)" <houzj(dot)fnst(at)fujitsu(dot)com>, shveta malik <shveta(dot)malik(at)gmail(dot)com>, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Ajin Cherian <itsajin(at)gmail(dot)com>, Dilip Kumar <dilipbalaut(at)gmail(dot)com>, Nisha Moond <nisha(dot)moond412(at)gmail(dot)com>, "Hayato Kuroda (Fujitsu)" <kuroda(dot)hayato(at)fujitsu(dot)com>, Bertrand Drouvot <bertranddrouvot(dot)pg(at)gmail(dot)com>, Bharath Rupireddy <bharath(dot)rupireddyforpostgres(at)gmail(dot)com>, Peter Eisentraut <peter(dot)eisentraut(at)enterprisedb(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Ashutosh Sharma <ashu(dot)coek88(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
Subject: Re: Synchronizing slots from primary to standby
Date: 2024-03-05 03:45:20
Message-ID: CAA4eK1+ig1=+CFvJVKqu7TcHF28ATemUysnppopwTsCjrXLbYg@mail.gmail.com
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On Tue, Mar 5, 2024 at 6:10 AM Peter Smith <smithpb2250(at)gmail(dot)com> wrote:
>
> ======
> src/backend/replication/walsender.c
>
> 5. NeedToWaitForWal
>
> + /*
> + * Check if the standby slots have caught up to the flushed position. It
> + * is good to wait up to the flushed position and then let the WalSender
> + * send the changes to logical subscribers one by one which are already
> + * covered by the flushed position without needing to wait on every change
> + * for standby confirmation.
> + */
> + if (NeedToWaitForStandbys(flushed_lsn, wait_event))
> + return true;
> +
> + *wait_event = 0;
> + return false;
> +}
> +
>
> 5a.
> The comment (or part of it?) seems misplaced because it is talking
> WalSender sending changes, but that is not happening in this function.
>

I don't think so. This is invoked only by walsender and a static
function. I don't see any other better place to mention this.

> Also, isn't what this is saying already described by the other comment
> in the caller? e.g.:
>

Oh no, here we are explaining the wait order.

--
With Regards,
Amit Kapila.

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