On Wed, Sep 13, 2006 at 03:12:22PM +0200, Matthieu Guamis wrote:
> If I use "VACUUM ANALYSE maTable" after CREATE AS of the DROP/CREATE
> AS/INSERT statements then INSERT commits in a few seconds.
> Documentation says :"VACUUM ANALYZE: Updates statistics used by the
> planner to determine the most efficient way to execute a query."
Are you running autovacuum? If so then that might explain why the
query runs faster after waiting a little while. When you first
create the table the planner doesn't have good statistics about it
so it might use a sub-optimal query plan. After autovacuum runs
and analyzes the table, the statistics are more accurate and the
planner uses a better plan. When you delete rows rather than drop
and recreate the table, the planner can use statistics based on the
table's previous contents and choose a good plan right away. You
could use EXPLAIN ANALYZE on the problematic SELECT statement to
see if this is what's happening.
--
Michael Fuhr
