About Access paths

From: Ioannis Theoharis <theohari(at)ics(dot)forth(dot)gr>
To: pgsql-general(at)postgresql(dot)org
Subject: About Access paths
Date: 2005-03-06 20:38:22
Message-ID: Pine.GSO.4.58.0503062229230.14330@ourania.ics.forth.gr
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in case that one has a table R(att0 int4, att1 int4), an index on att1
and a query selecting only att1 whith a range condition over att1, then
the optimal access path for a rdbms would be "INDEX ONLY SCAN", which means
scan only the index, and not the relation (all the needed information
exists in index, because the select clause has only the att1 attribute).
This access path is selected in this case by Oracle.

As far as i can see, postgresql select a simple "INDEX SCAN using index"
on table.

Is there any tuning that one has to do, in order to make postgresql's
optimizer to select "INDEX ONLY SCAN" ?
Or postgresql doesn't support this feature at all?


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