From: | Michael Fuhr <mike(at)fuhr(dot)org> |
---|---|
To: | Matthieu Guamis <matthieu(dot)guamis(at)axege(dot)com> |
Cc: | pgsql-novice(at)postgresql(dot)org |
Subject: | Re: [RESOLVED] INSERT does not finish except if it is carried |
Date: | 2006-09-13 13:35:14 |
Message-ID: | 20060913133514.GA88599@winnie.fuhr.org |
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Lists: | pgsql-general pgsql-novice |
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
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