Re: Can concurrent create index concurrently block each other?

I noticed this on PG 10 recently, while I agree it is an obsolete version.
pg_blocking_pids() showed that one of the CIC on a Table is blocked
by a CIC on another Table.

I saw them both created over a period of time after which I doubted
what was reported by pg_blocking_pids().

As it was PG 10, I could not see the phase of CIC and interestingly no wait
events.
Anyways, PG 10 is unsupported but I would try it on a newer version.

Curious to understand why this would have happened.

Regards,
Avi Vallarapu.

On Sun, Oct 15, 2023 at 2:35 PM Konstantin Knizhnik <knizhnik(at)garret(dot)ru>
wrote:

> One our customer complains that he spawned two `create index concurrently`
> for two different tables and both stuck in "waiting for old snapshots".
> I wonder if two CIC can really block each other in `
> WaitForOlderSnapshots`?
> I found the similar question in hacker archive:
>
>
> https://www.postgresql.org/message-id/flat/MWHPR20MB1421AEC7CEC67B159AC188F6A19A0%40MWHPR20MB1421.namprd20.prod.outlook.com
>
> but it is quite old (2016). Was the problem fixed since that time? And if
> not, why there it is not mentioned in CIC documentation that performing
> several CIC in parallel can cause "deadlock"?
>
> Thanks in advance,
> Konstantin
>

--
Regards,
Avinash Vallarapu
+1-902-221-5976