Re: Logical Replication - detail message with names of missing columns

Thank you for working on this.

At Mon, 7 Sep 2020 16:30:59 +0530, Bharath Rupireddy <bharath(dot)rupireddyforpostgres(at)gmail(dot)com> wrote in
> Hi,
>
> I observed that, in logical replication when a subscriber is missing
> some columns, it currently emits an error message that says "some"
> columns are missing(see logicalrep_rel_open()), but it doesn't specify
> what the missing column names are. The comment there also says that
> finding the missing column names is a todo item(/* TODO, detail
> message with names of missing columns */).
>
> I propose a patch to find the missing columns on the subscriber
> relation using the publisher relation columns and show them in the
> error message which can make the error more informative to the user.

+1 for objective. However, that can be done simpler way that doesn't
need additional loops by using bitmapset to hold missing remote
attribute numbers. This also make the variable "found" useless.

> Here's a snapshot how the error looks with the patch:
> 2020-09-04 01:00:36.721 PDT [843128] ERROR: logical replication
> target relation "public.test_1" is missing "b1, d1" replicated columns
> 2020-09-04 01:00:46.784 PDT [843132] ERROR: logical replication
> target relation "public.test_1" is missing "b1" replicated columns
> 2020-09-06 21:24:53.645 PDT [902945] ERROR: logical replication
> target relation "public.test_1" is missing "a1, c1, d1, b1" replicated
> columns
>
> Thoughts?

FWIW, I would prefer that the message be like

logical replication target relation "public.test_1" is missing
replicated columns: "a1", "c1"

I'm not sure we need to have separate messages for singlar and plural.

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center