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From: p.luzanov@postgrespro.ru
To: David G. Johnston <david.g.johnston@gmail.com>
Cc: pluzanov@postgrespro.ru
Cc: pgsql-docs@lists.postgresql.org
Subject: Re: max_wal_size
Date: Thu, 28 May 2020 00:12:34 +0300
Message-ID: <8aac88e2a22cd84e50ee1a2bcf3da9b7@postgrespro.ru> (raw)
In-Reply-To: <CAKFQuwYOGSRbcWnSEo7vp7JJktdH9rKJM0T8Q3B6J0QJcq==hA@mail.gmail.com>
References: <159057129673.7025.17016799863173731176@wrigleys.postgresql.org>
	<CAKFQuwZOwfUwOxNh5KjUjCSFaecUWxtHEbPHEK8CJF1+zn9Bjg@mail.gmail.com>
	<92491c6d07a3216ef2caee8ef55c02b5@postgrespro.ru>
	<CAKFQuwYOGSRbcWnSEo7vp7JJktdH9rKJM0T8Q3B6J0QJcq==hA@mail.gmail.com>

David,

> For 0.5 you get 2/3rds consumption: ( n / ( 1 + 0.5  ) ) = n * 2/3

Exactly, for checkpoint_completion_target=0.5 the distance between 
checkpoints is 2/3 of max_wal_size.

But back to the documentation of max_wal_size.
"Maximum size to let the WAL grow to between automatic WAL checkpoints."

For me it looks like the distance between checkpoints is equal to 
max_wal_size.

English is not my native language, so I admit that I misunderstand the 
exact meaning of this phrase.

P.S. Sorry to post this topic twice.
https://www.postgresql.org/message-id/97af9ef7-d7d9-cfd0-a280-d400cf05c68a%40postgrespro.ru
-----
Pavel Luzanov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company





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