At 03:20 PM 21/11/2002 +0100, Eelco van Beek - IC&S wrote:
For what i know a LIMIT instruction should never result in a different
query execution scheme. A limit is always a query result subset and will
never involve the actual query itself. Subsequently analyze won't be able
to optimize anything because a query with limit clause cannot be more
efficient.
This is actually incorrect. To quote from the PostgreSQL manual:
Also, if you limit the number of tuples to return with a LIMIT clause,
the planner makes an appropriate interpolation between the endpoint
costs to estimate which plan is really the cheapest
The planner does know that indexes can be used to return data in sorted
order, so choosing to use the messageblk_idnr index is not a bad strategy
(for small amounts of data).
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