Postgres Pro
Downloads
Home   >   mailing lists

Thread: ill-planned queries inside a stored procedure

ill-planned queries inside a stored procedure

From
Gaetano Mendola
Date:
Hi all,
do you know any clean workaround at ill-planned queries inside a stored procedure?
Let me explain with an example:


empdb=# select count(*) from user_logs;
   count
---------
  5223837
(1 row)

empdb=# select count(*) from user_logs where id_user = 5024;
  count
--------
  239453
(1 row)

empdb=# explain analyze select login_time from user_logs where id_user = 5024 order by id_user_log desc limit 1;
                                                                      QUERY PLAN

-----------------------------------------------------------------------------------------------------------------------------------------------------
  Limit  (cost=0.00..22.62 rows=1 width=12) (actual time=3.921..3.922 rows=1 loops=1)
    ->  Index Scan Backward using user_logs_pkey on user_logs  (cost=0.00..5355619.65 rows=236790 width=12) (actual
time=3.918..3.918rows=1 loops=1) 
          Filter: (id_user = 5024)
  Total runtime: 3.963 ms
(4 rows)


same select in a prepared query ( I guess the stored procedure use same plan ):

empdb=# explain analyze execute test(5024);
                                                                        QUERY PLAN

--------------------------------------------------------------------------------------------------------------------------------------------------------
  Limit  (cost=759.60..759.61 rows=1 width=12) (actual time=45065.755..45065.756 rows=1 loops=1)
    ->  Sort  (cost=759.60..760.78 rows=470 width=12) (actual time=45065.748..45065.748 rows=1 loops=1)
          Sort Key: id_user_log
          ->  Index Scan using idx_user_user_logs on user_logs  (cost=0.00..738.75 rows=470 width=12) (actual
time=8.936..44268.087rows=239453 loops=1) 
                Index Cond: (id_user = $1)
  Total runtime: 45127.256 ms
(6 rows)


There is a way to say: replan this query at execution time ?


Regards
Gaetano Mendola

Re: ill-planned queries inside a stored procedure

From
andrew@pillette.com
Date:
I use "EXECUTE" inside a stored procedure for just this purpose. This is not the same as PREPARE/EXECUTE, it lets you
sendan arbitrary string as SQL within the procedure. You have to write the query text on the fly in the procedure,
whichcan be a little messy with quoting and escaping. 

Gaetano Mendola <mendola@bigfoot.com> wrote ..
> Hi all,
> do you know any clean workaround at ill-planned queries inside a stored
> procedure?

Re: ill-planned queries inside a stored procedure

From
Gaetano Mendola
Date:
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

andrew@pillette.com wrote:

| Gaetano Mendola <mendola@bigfoot.com> wrote ..
|
|>Hi all,
|>do you know any clean workaround at ill-planned queries inside a stored
|>procedure?
| I use "EXECUTE" inside a stored procedure for just this purpose. This is
| not the same as PREPARE/EXECUTE, it lets you send an arbitrary string as
| SQL within the procedure. You have to write the query text on the fly in
| the procedure, which can be a little messy with quoting and escaping.
|

Yes I knew, I wrote "clean workaround" :-)

I hate write in function piece of code like this:

~   [...]

~   my_stm := ''SELECT '' || my_operation || ''( '' || a_id_transaction;
~   my_stm := my_stm || '', '' || a_id_contract;
~   my_stm := my_stm || '', '' || quote_literal(a_date) || '') AS res'';

~   FOR my_record IN EXECUTE my_stm LOOP
~      IF my_record.res < 0 THEN
~         RETURN my_record.res;
~      END IF;

~      EXIT;
~   END LOOP;

~   [...]

note also that useless loop that is needed to retrieve the value!



Regards
Gaetano Mendola












-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.2.4 (MingW32)
Comment: Using GnuPG with Thunderbird - http://enigmail.mozdev.org

iD8DBQFBMLRE7UpzwH2SGd4RAv0TAJ9+IokZjaXIhgV5dOH86FCvzSnewQCgwqxD
nuW9joHmPxOnlRWrvhsKaag=
=Axb7
-----END PGP SIGNATURE-----