Re: WAL recycled despite logical replication slot

From: Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>
To: Jeff Janes <jeff(dot)janes(at)gmail(dot)com>
Cc: pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: WAL recycled despite logical replication slot
Date: 2019-09-20 15:27:16
Message-ID: 20190920152716.pftsnojxuzcfmgdf@development
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On Fri, Sep 20, 2019 at 08:45:34AM -0400, Jeff Janes wrote:
>While testing something else (whether "terminating walsender process due to
>replication timeout" was happening spuriously), I had logical replication
>set up streaming a default pgbench transaction load, with the publisher
>being 13devel-e1c8743 and subscriber being 12BETA4. Eventually I started
>getting errors about requested wal segments being already removed:
>10863 sub idle 00000 2019-09-19 17:14:58.140 EDT LOG: starting logical
>decoding for slot "sub"
>10863 sub idle 00000 2019-09-19 17:14:58.140 EDT DETAIL: Streaming
>transactions committing after 79/EB0B17A0, reading WAL from 79/E70736A0.
>10863 sub idle 58P01 2019-09-19 17:14:58.140 EDT ERROR: requested WAL
>segment 0000000100000079000000E7 has already been removed
>10863 sub idle 00000 2019-09-19 17:14:58.144 EDT LOG: disconnection:
>session time: 0:00:00.030 user=jjanes database=jjanes host=
>It had been streaming for about 50 minutes before the error showed up, and
>it showed right when streaming was restarting after one of the replication
>Is there an innocent explanation for this? I thought logical replication
>slots provided an iron-clad guarantee that WAL would be retained until it
>was no longer needed. I am just using pub/sub, none of the lower level

I think you're right - this should not happen with replication slots.
Can you provide more detailed setup instructions, so that I can try to
reproduce and investigate the isssue?


Tomas Vondra
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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