Re: file cloning in pg_upgrade and CREATE DATABASE

From: Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>
To: Michael Paquier <michael(at)paquier(dot)xyz>
Cc: pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: file cloning in pg_upgrade and CREATE DATABASE
Date: 2018-04-05 20:55:58
Message-ID: b898f2eb-d0c0-5ebf-2b77-cf04b7298e73@2ndquadrant.com
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I think we have raised a number of interesting issues here which require
more deeper consideration. So I suggest to set this patch to Returned
with feedback.

Btw., I just learned that copy_file_range() only works on files on the
same device. So more arrangements will need to be made for that.

> I have run some more tests on both macOS and Linux with ext4, and my> results are that the bigger the flush distance, the better. Before
we> made the adjustments for APFS, we had a flush size of 64kB, now it's
1MB> and 32MB on macOS. In my tests, I see 256MB as the best across
both> platforms, and not flushing early at all is only minimally worse.
Based on this, I suggest that we set the flush distance to 32MB on all
platforms. Not only is it faster, it avoids having different settings
on some platforms.

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

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