Horton

Re: ALTER TABLE .. DETACH PARTITION CONCURRENTLY

Alvaro Herrera <alvherre@alvh.no-ip.org>

View thread View on postgr.es
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Andy Fan <zhihui.fan1213@gmail.com>
Cc: Pg Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2020-10-15T01:08:40Z
Lists: pgsql-hackers 
On 2020-Oct-15, Andy Fan wrote:

> I think if it is possible to implement the detech with a NoWait option .
> 
> ALTER TABLE ... DETACH PARTITION ..  [NoWait].
> 
> if it can't get the lock, raise "Resource is Busy" immediately,
> without blocking others.  this should be a default behavior.   If
> people do want to keep trying, it can set a ddl_lock_timeout to
> 'some-interval',  in this case, it will still block others(so it can't
> be as good as what you are doing, but very simple),  however the user
> would know what would happen exactly and can coordinate with their
> application accordingly.   I'm sorry about this since it is a bit of
> off-topics or it has been discussed already.

Hi.  I don't think this has been discussed, but it doesn't really solve
the use case I want to -- in many cases where the tables are
continuously busy, this would lead to starvation.  I think the proposal
to make the algorithm work with reduced lock level is much more useful.

I think you can already do NOWAIT behavior, with LOCK TABLE .. NOWAIT
followed by DETACH PARTITION, perhaps with a nonzero statement timeout.

Commits

  1. Make detach-partition-concurrently-4 less timing sensitive

  2. Improve documentation on DETACH PARTITION lock levels

  3. Track detached partitions more accurately in partdescs

  4. Allow a partdesc-omitting-partitions to be cached

  5. Fix relcache inconsistency hazard in partition detach

  6. Don't add a redundant constraint when detaching a partition

  7. ALTER TABLE ... DETACH PARTITION ... CONCURRENTLY

  8. Let ALTER TABLE Phase 2 routines manage the relation pointer

  9. Check default partitions constraints while descending