SQL Statement cause delay on exceptional days to run

Question

Hi ,
We are running the same sql statement on daily basis.
5 days a week, it gets completed in 10 mins and once or, twice in a week , it takes 7 – 10 Hrs to execute.
what are the tuning methods and steps we can apply to know the real culprits.
Regards
Asif

Answer 1

Before you dive into reading books and other stuff, you can simply look at the execution plan of your Statement on SQL*PLUS.
It's very easy, just do the following with your SQL Statement on both cases when it takes 10 minutes and hours and compare the results.
DEV@TEST>
DEV@TEST> SET AUTOTRACE TRACEONLY
DEV@TEST>
DEV@TEST> SET TIMING ON
DEV@TEST>
DEV@TEST> SELECT * FROM USER_OBJECTS;
105 rows selected.
Elapsed: 00:00:00.01
Execution Plan
   0      SELECT STATEMENT Optimizer=ALL_ROWS (Cost=146 Card=1620 Byte
          s=259200)
   1    0   VIEW OF 'USER_OBJECTS' (VIEW) (Cost=146 Card=1620 Bytes=25
          9200)
   2    1     UNION-ALL
   3    2       FILTER
   4    3         TABLE ACCESS (FULL) OF 'OBJ$' (TABLE) (Cost=146 Card
          =1731 Bytes=136749)
   5    3         TABLE ACCESS (BY INDEX ROWID) OF 'IND$' (CLUSTER) (C
          ost=2 Card=1 Bytes=8)
   6    5           INDEX (UNIQUE SCAN) OF 'I_IND1' (INDEX (UNIQUE)) (
          Cost=1 Card=1)
   7    2       TABLE ACCESS (BY INDEX ROWID) OF 'LINK$' (TABLE) (Cost
          =0 Card=1 Bytes=88)
   8    7         INDEX (RANGE SCAN) OF 'I_LINK1' (INDEX) (Cost=0 Card
          =1)
Statistics
          0  recursive calls
          0  db block gets
        726  consistent gets
          0  physical reads
          0  redo size
       8804  bytes sent via SQL*Net to client
        574  bytes received via SQL*Net from client
          8  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
        105  rows processed
DEV@TEST>You should have an idea why there's a difference in execution time by comparing the results.
Regards,
Tony Garabedian