Re: shared_buffers smaller than max_wal_size

From: Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>
To: Vladimir Mihailenco <vladimir(dot)webdev(at)gmail(dot)com>
Cc: pgsql-general(at)postgresql(dot)org
Subject: Re: shared_buffers smaller than max_wal_size
Date: 2017-09-24 17:59:05
Message-ID: 282731b1-15dc-c36d-9470-89b142b096cd@2ndquadrant.com
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On 09/24/2017 11:03 AM, Vladimir Mihailenco wrote:
> Thanks for your response. Ss I understand it now the difference is
> that checkpoints are synchronous but dirty pages eviction from shared
> buffers are asynchronous, correct? How then Postgres ensures that OS
> writes data to the disk so WAL can be deleted?
>

The last step in a checkpoin is fsync() on the files. Without that, the
checkpoint is considered incomplete and the database won't rely on it.

regards

--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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