Re: Why we lost Uber as a user

Joshua D. Drake <jd@commandprompt.com>

From: "Joshua D. Drake" <jd@commandprompt.com>
To: Tom Lane <tgl@sss.pgh.pa.us>, Robert Haas <robertmhaas@gmail.com>
Cc: Stephen Frost <sfrost@snowman.net>, Alfred Perlstein <alfred@freebsd.org>, Geoff Winkless <pgsqladmin@geoff.dj>, Pg Hackers <pgsql-hackers@postgresql.org>
Date: 2016-08-03T18:56:04Z
Lists: pgsql-hackers
On 08/03/2016 11:23 AM, Tom Lane wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
>> I don't think they are saying that logical replication is more
>> reliable than physical replication, nor do I believe that to be true.
>> I think they are saying that if logical corruption happens, you can
>> fix it by typing SQL statements to UPDATE, INSERT, or DELETE the
>> affected rows, whereas if physical corruption happens, there's no
>> equally clear path to recovery.
>
> Well, that's not an entirely unreasonable point, but I dispute the
> implication that it makes recovery from corruption an easy thing to do.
> How are you going to know what SQL statements to issue?  If the master
> database is changing 24x7, how are you going to keep up with that?
>
> I think the realistic answer if you suffer replication-induced corruption
> is usually going to be "re-clone that slave", and logical rep doesn't
> really offer much gain in that.

Yes, it actually does. The ability to unsubscribe a set of tables, 
truncate them and then resubscribe them is vastly superior to having to 
take a base backup.

JD

>
> 			regards, tom lane
>
>


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  1. Advance backend's advertised xmin more aggressively.

  2. Improve snapshot manager by keeping explicit track of snapshots.