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Re: [PATCHES] VACUUM Improvements - WIP Patch

From: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
To: Abhijit Menon-Sen <ams(at)oryx(dot)com>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [PATCHES] VACUUM Improvements - WIP Patch
Date: 2008-09-01 06:29:29
Message-ID: 48BB8BC9.7080508@enterprisedb.com (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-patches
Abhijit Menon-Sen wrote:
> At 2008-08-25 10:24:01 +0300, heikki(at)enterprisedb(dot)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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