Horton

Re: Concurrent ALTER SEQUENCE RESTART Regression

Michael Paquier <michael.paquier@gmail.com>

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From: Michael Paquier <michael.paquier@gmail.com>
To: Jason Petersen <jason@citusdata.com>
Cc: PostgreSQL mailing lists <pgsql-bugs@postgresql.org>
Date: 2017-04-25T01:53:39Z
Lists: pgsql-bugs, pgsql-hackers 
On Tue, Apr 25, 2017 at 4:52 AM, Jason Petersen <jason@citusdata.com> wrote:
> While I understand the above workload is nonsensical, given the non-transactional behavior of ALTER SEQUENCE statements, previous PostgreSQL versions did not produce an error. It is likely applications have been coded with that assumption and will not deal well with the new behavior.

Yes, that's a bug.

> Having poked around the code a bit, I see the functions to access for sequence state have changed; I’m assuming this is an unintended side-effect of that change.
>
> I haven’t worked up a patch myself, but I have some hope someone more familiar with the underlying changes could make quick work of this.

I am working on it, will send a patch soon. My first intuition is that
this is some wild lock issue. I am checking as well other code paths.
An open item has been added for the time being.
-- 
Michael

Commits

  1. Make ALTER SEQUENCE, including RESTART, fully transactional.

  2. Modify sequence catalog tuple before invoking post alter hook.

  3. Use weaker locks when updating pg_subscription_rel

  4. Add pg_sequence system catalog

  5. Modify sequence state storage to eliminate dangling-pointer problem