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From: Bruce Momjian <bruce@momjian.us>
To: p.luzanov@postgrespro.ru
Cc: David G. Johnston <david.g.johnston@gmail.com>
Cc: pluzanov@postgrespro.ru
Cc: pgsql-docs@lists.postgresql.org
Subject: Re: max_wal_size
Date: Tue, 2 Jun 2020 15:35:47 -0400
Message-ID: <20200602193547.GA26240@momjian.us> (raw)
In-Reply-To: <b8e12875ebec9e6d3107df5fa1129e1e@postgrespro.ru>
References: <159057129673.7025.17016799863173731176@wrigleys.postgresql.org>
	<CAKFQuwZOwfUwOxNh5KjUjCSFaecUWxtHEbPHEK8CJF1+zn9Bjg@mail.gmail.com>
	<92491c6d07a3216ef2caee8ef55c02b5@postgrespro.ru>
	<CAKFQuwYOGSRbcWnSEo7vp7JJktdH9rKJM0T8Q3B6J0QJcq==hA@mail.gmail.com>
	<8aac88e2a22cd84e50ee1a2bcf3da9b7@postgrespro.ru>
	<CAKFQuwY=eGGGe7E9xHkdR+8YnKXeA8xp-qfRMGFJrs-Hsb_D5Q@mail.gmail.com>
	<b8e12875ebec9e6d3107df5fa1129e1e@postgrespro.ru>

On Thu, May 28, 2020 at 12:21:14PM +0300, p.luzanov@postgrespro.ru wrote:
> WAL |-----------|-----+-----|-----+-----|-----+----->
> 
>                    a           b           c  
> CP              +-----+     +-----+     +-----+
>                 b     e     b     e     b     e
> 
> Checkpointer process for point A starts at a(b) and ends at a(e).
> At the end of the work, CP makes a WAL record(plus symbol on WAL line).
> 
> Back to the max_wal_size description:
> "Maximum size to let the WAL grow to between automatic WAL checkpoints."
> 
> As I understand now, this is true when we talk about the checkpoint as a
> process.
> "Maximum size to let the WAL grow to between a(b) and b(e), between b(b) and c
> (e), etc".

What if we say:

	"Maximum size to let the WAL grow during automatic WAL checkpoints."

That highlights the "process" part.

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EnterpriseDB                             https://enterprisedb.com

  The usefulness of a cup is in its emptiness, Bruce Lee






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