Re: START_REPLICATION SLOT causing a crash in an assert build

[Jonathan S. Katz]

On 10/5/22 8:44 PM, Andres Freund wrote:

Hi,

On 2022-10-05 13:00:53 -0400, Jonathan S. Katz wrote:

On 9/27/22 1:52 AM, Kyotaro Horiguchi wrote:

Thanks!

At Mon, 26 Sep 2022 19:53:02 -0700, Andres Freund <and...@anarazel.de> wrote in

I wonder if the correct fix here wouldn't be to move the slotname out of
PgStat_StatReplSlotEntry?

Ugh. Right. I thought its outer struct as purely the part for the
common header. But we can freely place anything after the header
part. I moved it to the outer struct. I didn't clear that part in
pgstat_create_relation() because it is filled in immediately.

The attached is that.

This is still listed as an open item[1] for v15. Does this fix proposed
address the issue?

Unfortunately not - it doesn't even pass the existing tests
(test_decoding/001_repl_stats fails) :(.

Thanks for checking.

The reason for that is that with the patch nothing restores the slotname when
reading stats from disk. That turns out not to cause immediate issues, but at
the next shutdown the name won't be set, and we'll serialize the stats data
with an empty string as the name.

Ah.

I have two ideas how to fix it. As a design constraint, I'd be interested in
the RMTs opinion on the following:
Is a cleaner fix that changes the stats format (i.e. existing stats will be
thrown away when upgrading) or one that doesn't change the stats format
preferrable?

[My opinion, will let Michael/John chime in]



Thanks,

Jonathan

Ideally we would keep the stats on upgrade -- I think that's the better user experience.

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