Re: PostgreSQL logical decoder output plugin - unchanged toast data

From: Andres Freund <andres(at)anarazel(dot)de>
To: Georgy Buranov <gburanov(at)gmail(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: PostgreSQL logical decoder output plugin - unchanged toast data
Date: 2018-08-31 15:07:03
Message-ID: 20180831150703.fquj55xyqi2quqvn@alap3.anarazel.de
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Hi,

On 2018-08-31 16:55:37 +0200, Georgy Buranov wrote:
> Ok, thank you very much for your explanation,
>
> maybe I need something else in my case.
>
> As far as I understand, "On-disk toasted data for tuples from the WAL
> are not guaranteed in any way to be retain", but still, the LATEST
> value for the same cell should exist in postgres (in on-disk toast if
> it is huge, or not).

No, there's absolutely no such guarantee. The tuple could since have
been deleted, the column could have been updated to non-toasted, the
table could have been dropped, ...

> If I cannot get access to the on-disk toasted data for tuple from the
> WAL, can I have the access to the _latest_ value in this case
> (hopefully I describe it correct)

Again, you can set REPLICA IDENTITY to FULL and it'll be there.

Greetings,

Andres Freund

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