Date: Thu, 3 Jan 2019 22:15:49 -0300
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Yuri Niyazov <yuri@academia.edu>
Cc: pgsql-admin@lists.postgresql.org
Subject: Re: your mail
Message-ID: <201901040115.2m6fmgg2yfav@alvherre.pgsql>
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On 2019-Jan-03, Yuri Niyazov wrote:

> We are running Postgresql 9.3.8. We had something fairly surprising happen
> here the other day: we started reaching the vacuum limit, with our logs
> filling up with “WARNING:  database "mydb" must be vacuumed within
> 177009986 transactions” messages, hundreds of them per second, and we came
> dangerously close to experiencing a DB shutdown. *However*, there were only
> three things running that were writing to the database - a db-wide VACUUM
> that we manually started, a per-table autovacuum that postgres itself
> started, and a "write 1 row every 1-minute" cron job into a separate table
> that we use to track replication delay.

I suggest to consider an urgent upgrade to at least 9.3.11, but really
all the way to the end of 9.3, and quickly afterwards plan an upgrade to
the latest 9.4 in a short timeframe.  9.3.8 contains known bugs, which
the first upgrade gets you out of; but 9.3 as a whole is out of support
since a couple of months, so you'll be playing with fire until you're in
9.4.  Do not postpone to upgrade to 9.3.latest while planning the upgrade
to 9.4, though.

I wonder if you fell prey to this weird behavior:
https://postgr.es/m/CAMkU=1yE4YyCC00W_GcNoOZ4X2qxF7x5DUAR_kMt-Ta=YPyFPQ@mail.gmail.com

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