Re: getting "ERROR: tuple concurrently updated" during concurrent grant/revoke operations (9.2.13)

Hi,

On 2015-06-24 10:43:22 -0500, Merlin Moncure wrote:
> I was experiencing a problem where a script which was simultaneously
> loading multiple database backups to private schemas was reliably
> drawing the error, "ERROR:  tuple concurrently updated" during
> grant/revoke steps of the restore.  (The problem isn't at all serious
> because the impacted statement is irrelevant to this server.)  If I
> create a file,

> breakit.sql:
> GRANT ALL ON SCHEMA public TO PUBLIC;
> REVOKE ALL ON SCHEMA public FROM PUBLIC;
>
> and bench it, it immediately draws the error:
> [merlin@mernix ~]# pgbench -n -c16 -T30 -f breakit.sql postgres
> Client 4 aborted in state 0: ERROR:  tuple concurrently updated
> Client 2 aborted in state 0: ERROR:  tuple concurrently updated

To me that's not a bug. There's lots and lots of ways to get 'ERROR:
tuple concurrently updated' errors when doing catalog changes
concurrently. There's been a fair amount of work (particularly from
Robert) reducing the amount; but it's never been claimed to be complete.

I do think it'd be a good idea to fix occurrances, but I don't think
that's stuff amounting to a bug, which'd then entail backpatching.

In the specific case here you have an actual problem with your data
loading procedures - if they concurrenty affect the same schema,
including revoking permisssions - you'll possibly have more troubles
than just this. Actual users of, in this case, the public schema in
already existing schemas won't like this for example. And there
e.g. very well might be an extension in public schema.

Greetings,

Andres Freund