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From: Dianne Skoll <dfs@roaringpenguin.com>
To: pgsql-admin@lists.postgresql.org
Subject: Re: Reliable WAL file shipping over unreliable network
Date: Wed, 28 Feb 2018 14:53:41 -0500
Message-ID: <20180228145341.0fdf5414@hydrogen.roaringpenguin.com> (raw)
In-Reply-To: <33220469-5BB2-4A40-8F56-8F4F392C95B3@icloud.com>
References: <dd116172-3ddf-ee56-57f3-6e18d49abf8e@shopzeus.com>
	<400AC9CD-1E43-422C-A689-70BDBAFF231E@elevated-dev.com>
	<ee3ae4be-ab24-8443-82c1-95bcd4f86a63@shopzeus.com>
	<debd4205-e27a-cd9d-9169-6748e65083a2@shopzeus.com>
	<BA4A1866-95B0-49C6-8CD1-3D1B60A7837E@elevated-dev.com>
	<CF30D15A-BD42-42A7-9AD3-BB69AF9E8047@icloud.com>
	<D5B11CF5-E816-435B-BFB8-1226E23C046A@elevated-dev.com>
	<37C5A42B-4CDD-4F01-8F1E-1B185C1819B9@icloud.com>
	<20180228132620.2c882f84@hydrogen.roaringpenguin.com>
	<33220469-5BB2-4A40-8F56-8F4F392C95B3@icloud.com>

On Wed, 28 Feb 2018 13:49:33 -0500
Rui DeSousa <rui.desousa@icloud.com> wrote:

> Really? I think you really need to think about it.  You are dealing
> with a race condition.

You are not correct.

1) rsync copies the source file to a temporary file on the destination.

2) If and only if step (1) is successful, rsync renames the temporary
file to the final filename.

3) If and only if step (2) is successful, rsync sets the timestamp on
the destination file to match that of the source file, assuming the
--archive or similar command-line option was given.

There is no possible sequence of events that could give you a destination
file with the same size and timestamp as the source file and yet be
incorrect (just so long as the source file has stayed the same.)

Regards,

Dianne.




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