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index scan of whole table, can't see why

From: "Dan Langille" <dan(at)langille(dot)org>
To: pgsql-performance(at)postgresql(dot)org
Subject: index scan of whole table, can't see why
Date: 2005-01-20 01:37:59
Message-ID: 41EEC527.22215.A7AAF84@localhost (view raw or flat)
Thread:
Lists: pgsql-performance
Hi folks,

Running on 7.4.2, recently vacuum analysed the three tables in 
question.

The query plan in question changes dramatically when a WHERE clause 
changes from ports.broken to ports.deprecated.  I don't see why.  
Well, I do see why: a sequential scan of a 130,000 rows.  The query 
goes from 13ms to 1100ms because the of this.  The full plans are at 
http://rafb.net/paste/results/v8ccvQ54.html

I have tried some tuning by:

  set effective_cache_size to 4000, was 1000
  set random_page_cost to 1, was 4

The resulting plan changes, but no speed improvment, are at 
http://rafb.net/paste/results/rV8khJ18.html

Any suggestions please?  

-- 
Dan Langille : http://www.langille.org/
BSDCan - The Technical BSD Conference - http://www.bsdcan.org/


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