Re: Function to move the position of a replication slot

From: Magnus Hagander <magnus(at)hagander(dot)net>
To: Craig Ringer <craig(at)2ndquadrant(dot)com>
Cc: Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Andres Freund <andres(at)anarazel(dot)de>, Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Function to move the position of a replication slot
Date: 2017-08-31 12:19:08
Message-ID: CABUevEz0OSH+z-HtSoHuioEcvzD=+AADvZjvx2-yxhHM4+8-ow@mail.gmail.com
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On Thu, Aug 17, 2017 at 2:19 AM, Craig Ringer <craig(at)2ndquadrant(dot)com> wrote:

> On 17 August 2017 at 07:30, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>
> wrote:
>
>>
>> Definitely agreed on that. Any move function would need to check if
>> the WAL position given by caller is already newer than what's
>> available in the local pg_wal (minimum of all other slots), with a
>> shared lock that would need to be taken by xlog.c when recycling past
>> segments. A forward function works on a single entry, which should be
>> disabled at the moment of the update. It looks dangerous to me to do
>> such an operation if there is a consumer of a slot currently on it.
>>
>>
> pg_advance_replication_slot(...)
>
> ERROR's on logical slot, for now. Physical slots only.
>
> Forward-only.
>
> Future work to allow it to use the logical decoding infrastructure to
> fast-forward a slot by reading only catalog change information and
> invalidations, either via a dummy output plugin that filters out all xacts,
> or by lower level use of the decoding code.
>
> Reasonable?
>
>
PFA an updated and rebased patch.

Rebased. Now named pg_advance_replication_slot. ERROR on logical slots.
Forward only.

I think that, in the end, covered all the comments?

--
Magnus Hagander
Me: https://www.hagander.net/ <http://www.hagander.net/>
Work: https://www.redpill-linpro.com/ <http://www.redpill-linpro.com/>

Attachment Content-Type Size
pg_advance_replication_slot.patch text/x-patch 4.5 KB

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