Re: repeated decoding of prepared transactions

Hi,

On 2021-02-19 13:50:52 +1100, Ajin Cherian wrote:
> From 129947ab2d0ba223862ed1c87be0f96b51645ba0 Mon Sep 17 00:00:00 2001
> From: Ajin Cherian <ajinc@fast.au.fujitsu.com>
> Date: Thu, 18 Feb 2021 20:18:16 -0500
> Subject: [PATCH] Don't allow repeated decoding of prepared transactions.
> 
> Enforce full snapshot while decoding with two-phase enabled. This
> allows the decoder to differentiate between prepared transaction that
> were sent prior to restart and prepared transactions that were not sent
> because they were prior to consistent snapshot.

Isn't this an *extremely* expensive solution? Maintaining a full
snapshot is pretty darn expensive - so expensive that it's repeatedly
been a problem even just for building the initial snapshot (to the point
of being inable to do so). And that's typically a comparatively rare
operation, not something continual - but what you're proposing is a cost
paid during ongoing replication.

Greetings,

Andres Freund