From: Tom Lane <tgl@sss.pgh.pa.us>
To: Michael Paquier <michael@paquier.xyz>
cc: pgsql-hackers@lists.postgresql.org
Subject: Re: Gripes about walsender command processing
In-reply-to: <20200915050655.GN2183@paquier.xyz>
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Comments: In-reply-to Michael Paquier <michael@paquier.xyz>
	message dated "Tue, 15 Sep 2020 14:06:55 +0900"
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Date: Tue, 15 Sep 2020 14:48:55 -0400
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Michael Paquier <michael@paquier.xyz> writes:
> On Mon, Sep 14, 2020 at 11:34:44PM -0400, Tom Lane wrote:
>> (I don't quite follow your comment about repslot drop, btw.)

> There is already a command tag equivalent to DROP_REPLICATION_SLOT:
> $ git grep REPLICATION -- */cmdtaglist.h
> src/include/tcop/cmdtaglist.h:PG_CMDTAG(CMDTAG_DROP_REPLICATION_SLOT,
> "DROP REPLICATION SLOT", false, false, false)

[ blink ... ]  So why is it that DropReplicationSlot does

	SetQueryCompletion(&qc, CMDTAG_DROP_REPLICATION_SLOT, 0);
	EndCommand(&qc, DestRemote, false);

when the caller will immediately after that do

	SetQueryCompletion(&qc, CMDTAG_SELECT, 0);
	EndCommand(&qc, DestRemote, true);

StartLogicalReplication has a similar weirdness.
The more I look at this code, the more broken it seems.

Anyway, independently of whether walsender should be sending multiple
command-complete messages, I don't think I really approve of including
replication commands in the CommandTag enum.  It still seems like a
type pun.  However, it looks like we'd have to duplicate
SetQueryCompletion/EndCommand if we don't want to do that, so maybe
I'd better just hold my nose and do it that way.

			regards, tom lane