Subject: Re: PATCH: Exclude unlogged tables from base backups
To: pgsql-hackers@lists.postgresql.org
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From: David Steele <david@pgmasters.net>
Message-ID: <b5b63d5c-2552-4b13-0fe5-844901eefeea@pgmasters.net>
Date: Tue, 12 Dec 2017 18:24:23 -0500
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Hi Michael,

On 12/12/17 6:08 PM, Michael Paquier wrote:
> 
>> If the forks are written out of order (i.e. main before init), which is
>> definitely possible, then I think worst case is some files will be backed up
>> that don't need to be.  The main fork is unlikely to be very large at that
>> point so it doesn't seem like a big deal.
> 
> As far as I recall the init forks are logged before the main forks. I
> don't think that we should rely on that assumption though to be always
> satisfied.

Indeed, nothing is sure until a checkpoint.  Until then we must assume 
writes are random.

>> Well, I would be happy if you had a look!
> 
> You can count me in. I think that this patch has value for some
> dedicated workloads. 

Thanks!

> It is a waste to backup stuff that will be
> removed at recovery anyway.

It also causes confusion when the recovered database is smaller than the 
backup.  I can't tell you how many times I have answered this question...

-- 
-David
david@pgmasters.net