Re: Logical replication error "no record found" /* shouldn't happen */

On 2021-Jul-23, Andrey Borodin wrote:

> Hi!
>
> From time to time I observe $subj on clusters using logical replication.
> I most of cases there are a lot of other errors. Probably $subj condition should be kind of impossible without other problems.
> I propose to enhance error logging of XLogReadRecord() in ReadPageInternal().

Hmm.

A small problem in this patch is that XLogReaderValidatePageHeader
already sets errormsg_buf; you're overwriting that. I suggest to leave
that untouched. There are other two cases where the problem occurs in
page_read() callback; ReadPageInternal explicitly documents that it
doesn't set the error in that case. We have two options to deal with
that:

1. change all existing callbacks to set the errormsg_buf depending on
what actually fails, and then if they return failure without an error
message, add something like your proposed message.
2. throw error directly in the callback rather than returning. I don't
think this strategy actually works

I attach a cut-down patch that doesn't deal with the page_read callbacks
issue, just added stub comments in xlog.c where something should be
done.

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