Subject: Re: rmgr hooks and contrib/rmgr_hook
From: Simon Riggs <simon@2ndQuadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: ITAGAKI Takahiro <itagaki.takahiro@oss.ntt.co.jp>,
	pgsql-hackers@postgresql.org
In-Reply-To: <14451.1220369969@sss.pgh.pa.us>
References: <20080901121833.4A18.52131E4D@oss.ntt.co.jp>
	<1220345064.4371.275.camel@ebony.2ndQuadrant>
	<20080902174613.76B2.52131E4D@oss.ntt.co.jp>
	<1220348980.4371.316.camel@ebony.2ndQuadrant>
	<14451.1220369969@sss.pgh.pa.us>
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Date: Tue, 02 Sep 2008 17:24:33 +0100
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On Tue, 2008-09-02 at 11:39 -0400, Tom Lane wrote:
> Simon Riggs <simon@2ndQuadrant.com> writes:
> > On Tue, 2008-09-02 at 18:30 +0900, ITAGAKI Takahiro wrote:
> >> How about adding a new variable "recovery_preload_libaries" like as
> >> shared_preload_libraries? Rmgr libs in it are loaded only in startup
> >> process and only if recovery is needed.
> 
> > Good point. If others agree, I will re-implement this way.
> 
> Aside from the objections raised by Heikki

Heikki hasn't raised any. He was objecting to an additional thought from
Itagaki. There haven't been any other objections to this concept.

> , I'm not seeing the use-case
> for an rmgr that only executes during recovery; in fact I'm not entirely
> sure that I see a use-case for this entire patch.  Where are the WAL
> records that the "loadable rmgr" processes going to come from?

There is ample reason to do this. I covered this in my first post,
please re-read up thread. You have commented on this post already, so
I'm suprised by your comments.

Rmgr functions only execute during recovery, that is their role in life.
Except when we have WAL_DEBUG enabled they are never called elsewhere.

-- 
 Simon Riggs           www.2ndQuadrant.com
 PostgreSQL Training, Services and Support