Date: Fri, 28 Dec 2018 14:34:44 -0300
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Michael Paquier <michael@paquier.xyz>,
	"Tsunakawa, Takayuki" <tsunakawa.takay@jp.fujitsu.com>,
	Robert Haas <robertmhaas@gmail.com>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: removal of dangling temp tables
Message-ID: <201812281734.zwh3cexl4p2i@alvherre.pgsql>
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On 2018-Dec-28, Tom Lane wrote:

> I wrote:
> > Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> >> I looked at 
> >> https://github.com/postgrespro/pg_wait_sampling/blob/master/pg_wait_sampling.c
> >> https://github.com/citusdata/citus/search?q=pgproc&unscoped_q=pgproc
> >> and skimmed a few others can't find any instance where the full struct
> >> is used, as opposed to just a pointer to it.
> 
> > No, the point Michael is making is that the array stride in the ProcArray
> > is part of our ABI.  For example, accessing a PGPROC from its pgprocno
> > using the GetPGProcByNumber macro will be broken if we change the
> > struct size.  I do not think you can assume that no extension does that.
> 
> In fact, there's a counterexample right here in pg_wait_sampling:
> 
> https://github.com/postgrespro/pg_wait_sampling/blob/master/pg_wait_sampling.c#L343

Ughh.  I stand corrected.

This seems a terrible interface, from an ABI compatibility point of
view, and exposing proclist_node_get() as an inline function, doubly so.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services