Re: Reusing cached prepared statement slow after 5 executions

Dean Rasheed wrote:
>> I can confirm, when I call ps.setPrepareThreshold(1) the query is
slow
>> immediately, so the plan must be different with the server prepared
>> statements.
>
> You can confirm that from psql by doing
>
> EXPLAIN ANALYSE SELECT ... ;
>
> and then
>
> PREPARE ps( ... ) AS SELECT ... ;
> EXPLAIN ANALYSE EXECUTE ps ( ... ) ;
>
> using your query and the parameters in question.
>
> It is entirely possible that the plan chosen for the prepared
> statement will be worse than the one used when the parameters are
> known at planning time. The prepared statement doesn't know what
> parameters are going to be used, so it can't always come up with the
> best plan. See the notes in the PREPARE manual page:
> http://www.postgresql.org/docs/9.0/static/sql-prepare.html

Could the parameter cursor_tuple_fraction play a role here too?

Yours,
Laurenz Albe