How to find out the execution time of a sql inside a function

Question

Hi All,
I am writing one function. There is only one IN parameter. In that parameter, i will pass one SQL select statement. And I want the function to return the exact execution time of that SQL statement.
CREATE OR REPLACE FUNCTION function_name (p_sql IN VARCHAR2)
RETURN NUMBER
IS
exec_time NUMBER;
BEGIN
--Calculate the execution time for the incoming sql statement.
RETURN exec_time;
END function_name;
/

Answer 1

Please note that wrapping query in a "SELECT COUNT(*) FROM (<query>)" doesn't necessarily reflect the execution time of the stand-alone query because the optimizer is smart and might choose a completely different execution plan for that query.
A simple test case shows the potential difference of work performed by the database:
Oracle Database 10g Express Edition Release 10.2.0.1.0 - Production
Session altered.
SQL>
SQL> drop table count_test purge;
Table dropped.
Elapsed: 00:00:00.17
SQL>
SQL> create table count_test as select * from all_objects;
Table created.
Elapsed: 00:00:02.56
SQL>
SQL> alter table count_test add constraint pk_count_test primary key (object_id)
Table altered.
Elapsed: 00:00:00.04
SQL>
SQL> exec dbms_stats.gather_table_stats(ownname=>null, tabname=>'COUNT_TEST')
PL/SQL procedure successfully completed.
Elapsed: 00:00:00.29
SQL>
SQL> set autotrace traceonly
SQL>
SQL> select * from count_test;
5326 rows selected.
Elapsed: 00:00:00.10
Execution Plan
Plan hash value: 3690877688
| Id  | Operation         | Name       | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT  |            |  5326 |   431K|    23   (5)| 00:00:01 |
|   1 |  TABLE ACCESS FULL| COUNT_TEST |  5326 |   431K|    23   (5)| 00:00:01 |
Statistics
          1  recursive calls
          0  db block gets
        419  consistent gets
          0  physical reads
          0  redo size
     242637  bytes sent via SQL*Net to client
       4285  bytes received via SQL*Net from client
        357  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
       5326  rows processed
SQL>
SQL> select count(*) from (select * from count_test);
Elapsed: 00:00:00.00
Execution Plan
Plan hash value: 572193338
| Id  | Operation             | Name          | Rows  | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT      |               |     1 |     5   (0)| 00:00:01 |
|   1 |  SORT AGGREGATE       |               |     1 |            |          |
|   2 |   INDEX FAST FULL SCAN| PK_COUNT_TEST |  5326 |     5   (0)| 00:00:01 |
Statistics
          1  recursive calls
          0  db block gets
         16  consistent gets
          0  physical reads
          0  redo size
        412  bytes sent via SQL*Net to client
        380  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed
SQL>As you can see the number of blocks processed (consistent gets) is quite different. You need to actually fetch all records, e.g. using a PL/SQL block on the server to find out how long it takes to process the query, but that's not that easy if you want to have an arbitrary query string as input.
Regards,
Randolf
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http://oracle-randolf.blogspot.com/
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