Date: Thu, 6 May 2021 13:32:08 -0400
From: =?iso-8859-1?Q?=C1lvaro?= Herrera <alvherre@alvh.no-ip.org>
To: Pavel Luzanov <p.luzanov@postgrespro.ru>
Cc: Amit Langote <amitlangote09@gmail.com>,
	Justin Pryzby <pryzby@telsasoft.com>, Tom Lane <tgl@sss.pgh.pa.us>,
	"pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>
Subject: Re: ALTER TABLE .. DETACH PARTITION CONCURRENTLY
Message-ID: <20210506173208.GA29458@alvherre.pgsql>
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On 2021-May-05, Pavel Luzanov wrote:

> Hello,
> 
> I found this in the documentation, section '5.11.3. Partitioning Using
> Inheritance'[1]:
> "Some operations require a stronger lock when using declarative partitioning
> than when using table inheritance. For example, removing a partition from a
> partitioned table requires taking an ACCESS EXCLUSIVE lock on the parent
> table, whereas a SHARE UPDATE EXCLUSIVE lock is enough in the case of
> regular inheritance."
> 
> This point is no longer valid with some restrictions. If the table has a
> default partition, then removing a partition still requires taking an ACCESS
> EXCLUSIVE lock.

Hmm, are there any other operations for which the partitioning command
takes a strong lock than the legacy inheritance corresponding command?
If there aren't any, then it's okay to delete this paragraph as in the
proposed patch.  But if there are any, then I think we should change the
example to mention that other operation.  I'm not sure what's a good way
to verify that, though.

Also, it remains true that without CONCURRENTLY the DETACH operation
takes AEL.  I'm not sure it's worth pointing this out in this paragraph.

> May be make sense to add some details about DETACH CONCURRENTLY to the
> section '5.11.2.2. Partition Maintenance' and completely remove this point?

Maybe you're right, though.

-- 
Álvaro Herrera                            39°49'30"S 73°17'W
"Las mujeres son como hondas:  mientras más resistencia tienen,
 más lejos puedes llegar con ellas"  (Jonas Nightingale, Leap of Faith)