Sql performance test

Question

Hi,
i'm dealing with a few statements.
I think their speed could be improved and i'm doing some changes.
The question is, as i'm launching these query a lot of time the data is being cached.
Thus explain plans doesn't helps me so much..
Is there a way to avoid the usage of buffered data?
eg. alter system flush buffer_cache; is sufficient?
Thanks
Acr

Answer 1

This because i wish to be sure that the cache is not
wasted by this object (i mean gb of data..)Full scans doesn't waste cache that much because data blocks are put on the very end of LRU queue and they simply reuse each other.
"I would pay attention to "logical I/O" (consistent
gets), and compare the number of rows returned to the
number of in-buffer block requests."use simply autotrace in SQL*Plus and pay attention to statistic consistent gets
SQL> create table source as select * from dba_source;
Table created.
Elapsed: 00:00:06.82
SQL> create index src_idx on source (line);
Index created.
Elapsed: 00:00:02.89
SQL> exec dbms_stats.gather_table_stats (user, 'source', cascade=>true)
PL/SQL procedure successfully completed.
Elapsed: 00:00:06.14
SQL> set autot traceonly
SQL> select line from source where line = 1;
5293 rows selected.
Elapsed: 00:00:00.17
Execution Plan
Plan hash value: 452987003
| Id  | Operation        | Name    | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT |         |   255 |  1020 |     3   (0)| 00:00:01 |
|*  1 |  INDEX RANGE SCAN| SRC_IDX |   255 |  1020 |     3   (0)| 00:00:01 |
Predicate Information (identified by operation id):
   1 - access("LINE"=1)
Statistics
          1  recursive calls
          0  db block gets
        366  consistent gets
          0  physical reads
          0  redo size
      71602  bytes sent via SQL*Net to client
       4256  bytes received via SQL*Net from client
        354  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
       5293  rows processed
SQL> select /*+ full (source) */ line from source where line = 1;
5293 rows selected.
Elapsed: 00:00:05.28
Execution Plan
Plan hash value: 1389487928
| Id  | Operation         | Name   | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT  |        |   255 |  1020 |  2182   (2)| 00:00:27 |
|*  1 |  TABLE ACCESS FULL| SOURCE |   255 |  1020 |  2182   (2)| 00:00:27 |
Predicate Information (identified by operation id):
   1 - filter("LINE"=1)
Statistics
          1  recursive calls
          0  db block gets
      10000  consistent gets
       7797  physical reads
          0  redo size
      71602  bytes sent via SQL*Net to client
       4256  bytes received via SQL*Net from client
        354  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
       5293  rows processed
SQL> If you want even more detailed compare then go to http://asktom.oracle.com/tkyte/runstats.html and install this package
There are quite many threads on http://asktom.oracle.com how to use it and what measurements are most important.
Gints Plivna
http://www.gplivna.eu