Subject: Re: file cloning in pg_upgrade and CREATE DATABASE
From: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
To: Michael Paquier <michael@paquier.xyz>
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Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Organization: 2ndQuadrant
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Date: Thu, 5 Apr 2018 16:55:58 -0400
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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