Subject: Re: replication_slots usability issue
To: Andres Freund <andres@anarazel.de>, Michael Paquier <michael@paquier.xyz>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>,
 pgsql-hackers <pgsql-hackers@postgresql.org>
References: <56672097-711c-126a-a63e-04e7940110ad@commandprompt.com>
 <20181029190218.uejy5cvgzygwrguy@alvherre.pgsql>
 <20181029191304.lbsmhshkyymhw22w@alap3.anarazel.de>
 <20181030025109.GD1644@paquier.xyz>
 <20181030175254.wqircsg36vblpmw5@alap3.anarazel.de>
From: "Joshua D. Drake" <jd@commandprompt.com>
Organization: Command Prompt, Inc.
Message-ID: <47ff1ce0-498b-e305-9c72-b0cdcf41e1ce@commandprompt.com>
Date: Tue, 30 Oct 2018 11:02:04 -0700
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On 10/30/18 10:52 AM, Andres Freund wrote:
> On 2018-10-30 11:51:09 +0900, Michael Paquier wrote:
>> On Mon, Oct 29, 2018 at 12:13:04PM -0700, Andres Freund wrote:
>>> I don't think this quite is the problem. ISTM the issue is rather that
>>> StartupReplicationSlots() *needs* to check whether wal_level > minimal,
>>> and doesn't. So you can create a slot, shutdown, change wal_level,
>>> startup. A slot exists but won't work correctly.
>> It seems to me that what we are looking for is just to complain at
>> startup if we find any slot data and if trying to start up with
>> wal_level = minimal.
> Right, we really should just call CheckSlotRequirements() before doing
> so. I'll make it so, once I'm actually awake and had some coffee.

Why not just disable the slot and report an INFO: line?


JD


>
>
>> Er...  At the same time, shouldn't RestoreSlotFromDisk() *not* use PANIC
>> if more slots are found in pg_replslot than max_replication_slots can
>> handle.  A FATAL is fine at startup, PANIC blows up a core file, which
>> is clearly overdoing it if the goal is to give a recommendation at the
>> end.
> I can't get particularly excited about this. I guess we can change it,
> but I'd only do so in master.
>
>
> Greetings,
>
> Andres Freund
>

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