Date: Sat, 25 Aug 2018 07:43:03 -0700
From: Andres Freund <andres@anarazel.de>
To: Julien Riou <julien.riou@outlook.com>
Cc: "pgsql-admin@lists.postgresql.org" <pgsql-admin@lists.postgresql.org>
Subject: Re: ERROR:  no known snapshots
Message-ID: <20180825144303.2cbtf7fyor7mkpvm@alap3.anarazel.de>
References: 
 <DB5PR0201MB17507769C5709234B25A409BE2350@DB5PR0201MB1750.eurprd02.prod.outlook.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: 
 <DB5PR0201MB17507769C5709234B25A409BE2350@DB5PR0201MB1750.eurprd02.prod.outlook.com>
Precedence: bulk

On 2018-08-25 07:04:14 +0000, Julien Riou wrote:
> Hello,
> 
> We have few highly available clusters with patroni managing PostgreSQL
> 9.6 (pgdg on debian stretch). We use logical decoding with wal2json to
> stream data to a remote platform. On a majority of clusters, it works
> like a charm. But for one, we have the following error right after
> decoding start:
> 
> [1353-1] LOG:  starting logical decoding for slot "*****"
> [1353-2] DETAIL:  streaming transactions committing after 321/292C06F0, reading WAL from 321/28BA9898
> [1354-1] LOG:  logical decoding found consistent point at 321/28BA9898
> [1354-2] DETAIL:  There are no running transactions.
> [1355-1] ERROR:  no known snapshots
> [1355-2] CONTEXT:  slot "*****", output plugin "wal2json", in the change callback, associated LSN 321/2A985A30
> 
> The only reference of the "no known snapshots" error is in PostgreSQL source
> code:
> https://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=src/backend/access/heap/tuptoaster.c;h=ade4bd142dfbd7ef3340495b06d1041e4032a17f;hb=ca3489e768990e32096f0f24d46d5f0b8b70cff4#l2320
> 
> Do you know what can cause this error?

Any chance that you're specifying the "include_unchanged_toast" option?
I briefly looked over wal2json (which isn't part of PG) and as far as I
can tell that option simply can't work correctly, and would cause errors
like the above.

Greetings,

Andres Freund