Horton

Re: [HACKERS] Concurrent ALTER SEQUENCE RESTART Regression

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
Cc: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, Petr Jelinek <petr.jelinek@2ndquadrant.com>, pgsql-hackers@postgresql.org, Noah Misch <noah@leadboat.com>, Jason Petersen <jason@citusdata.com>, Michael Paquier <michael.paquier@gmail.com>, PostgreSQL mailing lists <pgsql-bugs@postgresql.org>
Date: 2017-05-11T21:28:12Z
Lists: pgsql-bugs, pgsql-hackers 
Andres Freund <andres@anarazel.de> writes:
> On 2017-05-11 16:27:48 -0400, Peter Eisentraut wrote:
>> (So without contention fast-path locking beats the extra dance that
>> open_share_lock() does.)

> That's kind of surprising, I really wouldn't have thought it'd be faster
> without.  I guess it's the overhead of sigsetjmp().  Cool.

My results (posted nearby) lead me to suspect that the improvement
Peter sees from 9.1 to 9.2 has little to do with fastpath locking
and a lot to do with some improvement or other in subtransaction
lock management.

			regards, tom lane

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