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From: Ahmed Et-tanany <ahmed.ettanany@aiven.io>
Date: Thu, 29 Jan 2026 14:01:22 +0100
Message-ID: <CAD7nQBCwWj=v0QE6HL3BDOPrbqE1raniZ6DRPi_cyLxv81+HJQ@mail.gmail.com>
Subject: Re: [PATCH] Add max_logical_replication_slots GUC
To: Fujii Masao <masao.fujii@gmail.com>
Cc: =?UTF-8?Q?=C3=81lvaro_Herrera?= <alvherre@kurilemu.de>, 
	pgsql-hackers@lists.postgresql.org
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On Thu, Jan 29, 2026 at 12:39=E2=80=AFPM Fujii Masao <masao.fujii@gmail.com=
> wrote:

>
> Would something like max_logical_wal_senders also be needed for your
> purpose?
> Otherwise, logical replication connections could exhaust max_wal_senders
> and
> prevent physical replication connections from being established.
>
> That said, adding two separate GUC parameters (i.e.,
> max_logical_replication_slots
> and max_logical_wal_senders) for this purpose doesn't seem like a
> great solution,
> though...
>
>
That's a great point! I'm thinking we could potentially avoid
introducing a separate max_logical_wal_senders GUC by reusing
max_logical_replication_slots to decide whether a WAL sender can
start for logical replication.

This way, the limit on logical slots would also indirectly cap
the number of logical WAL senders, helping protect physical
replication connections without adding another configuration
parameter.

What do you think about this approach?

Best regards,

--=20
Ahmed Et-tanany
Aiven: https://aiven.io/

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<div dir=3D"ltr"><div dir=3D"ltr">On Thu, Jan 29, 2026 at 12:39=E2=80=AFPM =
Fujii Masao &lt;<a href=3D"mailto:masao.fujii@gmail.com">masao.fujii@gmail.=
com</a>&gt; wrote:</div><div class=3D"gmail_quote gmail_quote_container"><b=
lockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-le=
ft:1px solid rgb(204,204,204);padding-left:1ex">
<br>
Would something like max_logical_wal_senders also be needed for your purpos=
e?<br>
Otherwise, logical replication connections could exhaust max_wal_senders an=
d<br>
prevent physical replication connections from being established.<br>
<br>
That said, adding two separate GUC parameters (i.e.,<br>
max_logical_replication_slots<br>
and max_logical_wal_senders) for this purpose doesn&#39;t seem like a<br>
great solution,<br>
though...<br><br></blockquote><div><br></div>That&#39;s a great point! I=
9;m thinking we could potentially avoid<br>introducing a separate max_logic=
al_wal_senders GUC by reusing<br>max_logical_replication_slots to decide wh=
ether a WAL sender can<br>start for logical replication.<br><br>This way, t=
he limit on logical slots would also indirectly cap<br>the number of logica=
l WAL senders, helping protect physical<br>replication connections without =
adding another configuration<br>parameter.<br><br><div>What do you think ab=
out this approach?=C2=A0</div></div><div><br clear=3D"all"></div><div>Best =
regards,</div><div><br></div><span class=3D"gmail_signature_prefix">-- </sp=
an><br><div dir=3D"ltr" class=3D"gmail_signature"><div dir=3D"ltr"><span st=
yle=3D"color:rgb(0,0,0);font-family:monospace,monospace;font-size:10.7333px=
">Ahmed Et-tanany</span><br style=3D"color:rgb(0,0,0);font-family:monospace=
,monospace;font-size:10.7333px"><span style=3D"color:rgb(0,0,0);font-family=
:monospace,monospace;font-size:10.7333px">Aiven: </span><a href=3D"https://=
aiven.io/" rel=3D"nofollow" style=3D"color:rgb(132,0,50);background-color:t=
ransparent;font-weight:600;font-family:monospace,monospace;font-size:10.733=
3px" target=3D"_blank">https://aiven.io/</a></div></div></div>

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