Date: Mon, 23 Jul 2018 16:33:11 -0400
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Andres Freund <andres@anarazel.de>
Cc: Mariel Cherkassky <mariel.cherkassky@gmail.com>,
	pgsql-admin@lists.postgresql.org
Subject: Re: pg_authid has duplicated rows
Message-ID: <20180723203311.7isul7yxziiw7wbx@alvherre.pgsql>
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On 2018-Jul-23, Andres Freund wrote:

> Hi,
> 
> On 2018-07-23 21:03:32 +0300, Mariel Cherkassky wrote:
> > Today I faced a situation where I saw a postgresql 9.2 database that had
> > duplicated rows in pg_autid. I saw 6 roles while 3 of them were duplicated
> > (3 uniques rolenames in total). I checked and the oid of the duplicates
> > were the same oid as the originals. The solution was running vacuum on the
> > table but I wanted to understand how this situation was created ? Why even
> > with unique index on the rolname I saw duplicated values for rolname ?
> 
> That suggests some form of corruption. Which version of 9.2 did this
> occur on? Did you have any OS level crashes? Ran with fsync=off?

I have vague memories of seeing this recently.  Can you please show 

select xmin, xmax, ctid, oid, rolname from pg_authid

And the output of pg_controldata.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services