From: Tom Lane <tgl@sss.pgh.pa.us>
To: Don Seiler <don@seiler.us>
cc: Postgres General <pgsql-general@postgresql.org>
Subject: Re: Use of max_slot_wal_keep_size parameter
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Comments: In-reply-to Don Seiler <don@seiler.us>
	message dated "Tue, 26 Mar 2024 09:16:05 -0500"
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Date: Tue, 26 Mar 2024 10:29:21 -0400
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Don Seiler <don@seiler.us> writes:
> On Tue, Mar 26, 2024 at 9:09 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> ... So you could overshoot the specified target by
>> more or less the amount of WAL that could be emitted between two
>> checkpoints.  Perhaps it's tighter nowadays, but I really doubt that
>> it's exact-to-the-kilobyte-at-all-times.

> In this case, the total volume size was 60GB and we had the parameter set
> to 58GB but I imagine that can still be overwhelmed quickly. Maybe we
> should target a 20% buffer zone? We have wal_keep_size defaulted at 0.

Can you measure your WAL emission rate?  What you want I think is some
small multiple of the max amount of WAL emitted between checkpoints.

			regards, tom lane