Date: Wed, 8 Apr 2020 11:44:33 -0500
From: Justin Pryzby <pryzby@telsasoft.com>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: pgsql-hackers@lists.postgresql.org
Subject: Re: DETACH PARTITION and FOR EACH ROW triggers on partitioned tables
Message-ID: <20200408164433.GE2228@telsasoft.com>
References: <20200408152412.GZ2228@telsasoft.com>
 <20200408160239.GA13987@alvherre.pgsql>
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On Wed, Apr 08, 2020 at 12:02:39PM -0400, Alvaro Herrera wrote:
> On 2020-Apr-08, Justin Pryzby wrote:
> 
> > This seems to be a bug in master, v12, and (probably) v11, where "FOR EACH FOR"
> > was first allowed on partition tables (86f575948).
> > 
> > I thought this would work like partitioned indexes (8b08f7d48), where detaching
> > a partition makes its index non-inherited, and attaching a partition marks a
> > pre-existing, matching partition as inherited rather than creating a new one.
> 
> Hmm.  Let's agree to what behavior we want, and then we implement that.
> It seems to me there are two choices:
> 
> 1. on detach, keep the trigger but make it independent of the trigger on
> parent.  (This requires that the trigger is made dependent on the
> trigger on parent, if the table is attached as partition again;
> otherwise you'd end up with multiple copies of the trigger if you
> detach/attach multiple times).
> 
> 2. on detach, remove the trigger from the partition.
> 
> I think (2) is easier to implement, but (1) is the more convenient
> behavior.

At telsasoft, we don't care (we uninherit tables before ALTERing parents to
avoid disruptive locking and to avoid worst-case disk use).

(1) is consistent with the behavior for indexes, which is a slight advantage
for users' ability to understand and keep track of the behavior.  But adding
triggers is pretty different so I'm not sure it's a totally compelling
parallel.

-- 
Justin