>
> Are you running autovacuum?
Yes I am, ("autovacuum = on" in postgres.conf).
> You could use EXPLAIN ANALYZE
I'll do it soon.
Thank you very much for the explanation.
Michael Fuhr a écrit :
> 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.
>
>
