From: Bruce Momjian <bruce@momjian.us>
To: Kasper Kondzielski <kghost0@gmail.com>
Cc: pgsql-docs@lists.postgresql.org
Cc: jaroslaw.kijanowski@softwaremill.com
Subject: Re: Request for further clarification on synchronous_commit
Date: Tue, 18 Aug 2020 13:17:40 -0400
Message-ID: <20200818171740.GE27231@momjian.us> (raw)
In-Reply-To: <20200818145851.GB27231@momjian.us>
References: <159741195522.14321.13812604195366728976@wrigleys.postgresql.org>
<20200817174727.GA28474@momjian.us>
<CAFv2VPRPmoqpVPTR64jqebQZ6zOzeTCR4xN9c6zXhvaCc4nnNg@mail.gmail.com>
<20200818145851.GB27231@momjian.us>
On Tue, Aug 18, 2020 at 10:58:51AM -0400, Bruce Momjian wrote:
> Un, 'on' does _not_ apply the WAL data, and remote_apply does do remote
> fsync. If you want to go in order of severity, with the most severe
> first, it is:
>
> remote_apply
> on
> remote_write
> local
>
> This is seen in the C enum ordering for synchronous_commit, but in
> reverse order:
>
> typedef enum
> {
> SYNCHRONOUS_COMMIT_OFF, /* asynchronous commit */
> SYNCHRONOUS_COMMIT_LOCAL_FLUSH, /* wait for local flush only */
> SYNCHRONOUS_COMMIT_REMOTE_WRITE, /* wait for local flush and remote
> * write */
> SYNCHRONOUS_COMMIT_REMOTE_FLUSH, /* wait for local and remote flush */
> SYNCHRONOUS_COMMIT_REMOTE_APPLY /* wait for local flush and remote apply */
> } SyncCommitLevel;
Also, there is some logic to say that the postgresql.conf
synchronous_commit options list should be reordered from:
#synchronous_commit = on # synchronization level;
# off, local, remote_write, remote_apply, or on
to
#synchronous_commit = on # synchronization level;
# off, local, remote_write, on, or remote_apply
I think we should backpatch the doc changes, but maybe not the
postgresql.conf one --- I am not sure.
--
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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To: pgsql-docs@postgresql.org
Cc: bruce@momjian.us, kghost0@gmail.com, pgsql-docs@lists.postgresql.org, jaroslaw.kijanowski@softwaremill.com
Subject: Re: Request for further clarification on synchronous_commit
In-Reply-To: <20200818171740.GE27231@momjian.us>
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