Date: Mon, 10 Jan 2022 21:28:48 -0300
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Cc: Justin Pryzby <pryzby@telsasoft.com>,
	Tomas Vondra <tomas.vondra@enterprisedb.com>,
	Amit Kapila <amit.kapila16@gmail.com>,
	"houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>,
	Rahila Syed <rahilasyed90@gmail.com>,
	Peter Smith <smithpb2250@gmail.com>, pgsql-hackers@postgresql.org
Subject: Re: Column Filtering in Logical Replication
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On 2022-Jan-07, Peter Eisentraut wrote:

> ATExecReplicaIdentity(): Regarding the question of how to handle
> REPLICA_IDENTITY_NOTHING: I see two ways to do this.  Right now, the
> approach is that the user can set the replica identity freely, and we
> decide later based on that what we can replicate (e.g., no updates).
> For this patch, that would mean we don't restrict what columns can be
> in the column list, but we check what actions we can replicate based
> on the column list.  The alternative is that we require the column
> list to include the replica identity, as the patch is currently doing,
> which would mean that REPLICA_IDENTITY_NOTHING can be allowed since
> it's essentially a set of zero columns.
> 
> I find the current behavior a bit weird on reflection.  If a user
> wants to replicate on some columns and only INSERTs, that should be
> allowed regardless of what the replica identity columns are.

Hmm.  So you're saying that we should only raise errors about the column
list if we are publishing UPDATE or DELETE, but otherwise let the
replica identity be anything.  OK, I'll see if I can come up with a
reasonable set of rules ...

-- 
Álvaro Herrera         PostgreSQL Developer  —  https://www.EnterpriseDB.com/
"Before you were born your parents weren't as boring as they are now. They
got that way paying your bills, cleaning up your room and listening to you
tell them how idealistic you are."  -- Charles J. Sykes' advice to teenagers