Re: Synchronizing slots from primary to standby

On Tue, Mar 5, 2024 at 6:10 AM Peter Smith <smithpb2250@gmail.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.