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Re: Postgres 9.0 has a bias against indexes

From: Mladen Gogala <mladen(dot)gogala(at)vmsinfo(dot)com>
To: Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>
Cc: Igor Neyman <ineyman(at)perceptron(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, David Wilson <david(dot)t(dot)wilson(at)gmail(dot)com>, Kenneth Marshall <ktm(at)rice(dot)edu>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Postgres 9.0 has a bias against indexes
Date: 2011-01-27 20:44:10
Message-ID: 4D41D91A.3010308@vmsinfo.com (view raw or flat)
Thread:
Lists: pgsql-performance
On 1/27/2011 3:37 PM, Scott Marlowe wrote:
> On Thu, Jan 27, 2011 at 1:31 PM, Mladen Gogala
> <mladen(dot)gogala(at)vmsinfo(dot)com>  wrote:
>> There is INDEX UNIQUE SCAN PK_EMP.  Oracle will use an index.
> That's because Oracle has covering indexes.
>
I am not sure what you mean by "covering indexes" but I hope that for 
the larger table I have in mind,  indexes will be used.  For a small 
table like this, not using an index may actually be a better plan. I 
cannot compare because my development PostgreSQL cluster is on a much 
weaker machine than the development Oracle database.
I even looked into Wikipedia for the notion of "covering index" and it 
is defined as an index which contains all the data requested in a query. 
This is not the case, EMP is not an index-organized table. The only 
index used was the primary key, also available in the PostgreSQL version 
of the table.

-- 
Mladen Gogala
Sr. Oracle DBA
1500 Broadway
New York, NY 10036
(212) 329-5251
www.vmsinfo.com


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