To: Simon Riggs <simon@2ndQuadrant.com>
Cc: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>,
	Tom Lane <tgl@sss.pgh.pa.us>,
	ITAGAKI Takahiro <itagaki.takahiro@oss.ntt.co.jp>,
	pgsql-hackers@postgresql.org
Subject: Re: rmgr hooks and contrib/rmgr_hook
In-Reply-To: <1221470800.3913.1229.camel@ebony.2ndQuadrant> (Simon Riggs's
	message of "Mon\, 15 Sep 2008 10\:26\:40 +0100")
User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.1 (gnu/linux)
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>
	<1220372673.4371.465.camel@ebony.2ndQuadrant>
	<48CB72C8.1070700@enterprisedb.com>
	<1221470800.3913.1229.camel@ebony.2ndQuadrant>
From: Gregory Stark <stark@enterprisedb.com>
Organization: EnterpriseDB
Date: Mon, 15 Sep 2008 10:47:35 +0100
Message-ID: <87sks1oi4o.fsf@oxford.xeocode.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii

Simon Riggs <simon@2ndQuadrant.com> writes:

> On Sat, 2008-09-13 at 10:59 +0300, Heikki Linnakangas wrote:
>
>> The 2nd use case, however, I find pretty unconvincing. I can't think of 
>> a good example of that. Anything that needs to define its own resource 
>> manager is very low-level stuff, and probably needs to go into the core 
>> anyway.
>
> New indexes are a big one, but I listed others also.
>
> Indexes have always been able to be added dynamically. Now they can be
> recovered correctly as well.

Hm, so currently if you want to add a new indexam you can't just insert into
pg_am and make them recoverable. You basically have to build in your new index
access method into Postgres with the new rmgr. That is annoying and a problem
worth tackling.

But I'm a bit worried about having this be an external plugin. There's no way
to looking at a WAL file to know whether it will be recoverable with the
plugins available. Worse, there's a risk you could have a plugin but not the
*right* plugin. Perhaps this could be tackled simply by having startup insert
a record listing all the rmgr's in use with identifying information and their
version numbers.

-- 
  Gregory Stark
  EnterpriseDB          http://www.enterprisedb.com
  Ask me about EnterpriseDB's PostGIS support!