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From: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
To: Abhijit Menon-Sen <ams@oryx.com>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [PATCHES] VACUUM Improvements - WIP Patch
Date: Mon, 01 Sep 2008 09:29:29 +0300
Message-ID: <48BB8BC9.7080508@enterprisedb.com> (raw)
In-Reply-To: <20080901004646.GA24702@toroid.org>
References: <2e78013d0807132050j16cdc558s4dc3f889371a937d@mail.gmail.com>
	<200808230336.m7N3aOc15945@momjian.us>
	<b42b73150808240630r59ad34f3l24a980280cdc52d9@mail.gmail.com>
	<48B1831F.7010002@commandprompt.com>
	<48B1AB17.9010905@zeut.net>
	<25792.1219605368@sss.pgh.pa.us>
	<48B21989.9090200@zeut.net>
	<1683.1219631879@sss.pgh.pa.us>
	<48B25E11.5080803@enterprisedb.com>
	<20080901004646.GA24702@toroid.org>

Abhijit Menon-Sen wrote:
> At 2008-08-25 10:24:01 +0300, heikki@enterprisedb.com wrote:
>> My original plan was to enable index-only-scans using the DSM as well
>> for 8.4, but it's pretty clear at this point that I don't have the
>> time to finish that :-(.
> 
> I wonder how hard that would be.

It's doable, for sure.

The pieces I see as required for that are:
1. change the indexam API so that indexes can return tuples
2. make sure the DSM is suitable for index-only-scans. Ie. it must be 
completely up-to-date and WAL-logged, so that if the DSM says that all 
tuples on a page are visible, they really must be.
3. planner/stats changes, so that the planner can estimate how much of 
an index scan can be satisfied without looking at the heap (it's not an 
all-or-nothing plan-time decision with this design)

-- 
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com



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