Обсуждение: Partitions are not excluded in stored procedures
Hi there, I came across the following problem. Say I have a select query that given the appropriate where clauses it will only query the correct partitioned tables and not all of them. That can be examined by using the EXPLAIN. However the same select query used in a stored procedure will transverse all the tables regardless of the where clause parameters passed by the user as variables of the stored procedure . Is there any work around other than composing an EXECUTE "select ....."? Kind Regards Yiannis
Ioannis Anagnostopoulos <ioannis@anatec.com> writes:
> I came across the following problem. Say I have a select query that
> given the appropriate where clauses it will only query the correct
> partitioned tables and not all of them. That can be examined by using
> the EXPLAIN. However the same select query used in a stored procedure
> will transverse all the tables regardless of the where clause parameters
> passed by the user as variables of the stored procedure . Is there any
> work around other than composing an EXECUTE "select ....."?
Yeah, if the WHERE clauses that correspond to the partitioning
constraints contain parameters, the planner can't prove the exclusions
hold. So you have to use EXECUTE to get a one-shot plan. This will
be better in 9.2 (which, basically, will automatically recognize that
it needs to use one-shot plans).
regards, tom lane
On 05/06/2012 17:55, Tom Lane wrote: > Ioannis Anagnostopoulos<ioannis@anatec.com> writes: >> I came across the following problem. Say I have a select query that >> given the appropriate where clauses it will only query the correct >> partitioned tables and not all of them. That can be examined by using >> the EXPLAIN. However the same select query used in a stored procedure >> will transverse all the tables regardless of the where clause parameters >> passed by the user as variables of the stored procedure . Is there any >> work around other than composing an EXECUTE "select ....."? > Yeah, if the WHERE clauses that correspond to the partitioning > constraints contain parameters, the planner can't prove the exclusions > hold. So you have to use EXECUTE to get a one-shot plan. This will > be better in 9.2 (which, basically, will automatically recognize that > it needs to use one-shot plans). > > regards, tom lane When you say better in 9.2 you mean that we will be able to avoid the EXECUTE, and the plan will be, more or less, calculated per call without great performance hit? Regards and thank you Yiannis
I might be misunderstanding but I think that what Tom meant is that the EXPLAIN does not try to guess whether
the constraint will actually exclude some data, so it show you a pessimistic estimate of the cost.
If I'm right, using EXPLAIN ANALYZE should show that the query considers any constraint clauses in your query.
Cheers,
Marcelo Lacerda
On 06/06/2012 05:10 AM, Ioannis Anagnostopoulos wrote:
the constraint will actually exclude some data, so it show you a pessimistic estimate of the cost.
If I'm right, using EXPLAIN ANALYZE should show that the query considers any constraint clauses in your query.
Cheers,
Marcelo Lacerda
On 06/06/2012 05:10 AM, Ioannis Anagnostopoulos wrote:
On 05/06/2012 17:55, Tom Lane wrote:Ioannis Anagnostopoulos<ioannis@anatec.com> writes:When you say better in 9.2 you mean that we will be able to avoid the EXECUTE, and the plan will be, more or less, calculated per call without great performance hit?I came across the following problem. Say I have a select query thatYeah, if the WHERE clauses that correspond to the partitioning
given the appropriate where clauses it will only query the correct
partitioned tables and not all of them. That can be examined by using
the EXPLAIN. However the same select query used in a stored procedure
will transverse all the tables regardless of the where clause parameters
passed by the user as variables of the stored procedure . Is there any
work around other than composing an EXECUTE "select ....."?
constraints contain parameters, the planner can't prove the exclusions
hold. So you have to use EXECUTE to get a one-shot plan. This will
be better in 9.2 (which, basically, will automatically recognize that
it needs to use one-shot plans).
regards, tom lane
Regards and thank you
Yiannis