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Date: Wed, 27 May 2020 19:17:23 +0300
From: p.luzanov@postgrespro.ru
To: "David G. Johnston" <david.g.johnston@gmail.com>
Cc: pluzanov@postgrespro.ru, pgsql-docs@lists.postgresql.org
Subject: Re: max_wal_size
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David,

> This setting is the indirect means to ensure that the WAL directory
> doesn't get too large by forcing a checkpoint thus allowing the
> corresponding WAL to be removed.


This is a soft limit, ok.
But the question is a little different.

Suppose we have: version >= 11, no replication slots, archive_mode = 
off.
Checkpoint_timeout is big enough, so checkpoints triggered only by 
max_wal_size (1GB).
checkpoint_completion_target = 1.

What size of WAL files will be generated between checkpoints?
1GB or 0.5GB?

As I understand the description of max_wal_size(Maximum size to let the 
WAL grow to between automatic WAL checkpoints), the answer is 1GB.
But it seems that the right answer is 0.5GB.

-----
Pavel Luzanov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company