Oracle-L: DUAL revisited

From: John Zoltak <JohnZoltak_at_namfg.com>
Date: Fri, 02 Aug 2002 07:13:22 -0800
Message-ID: <F001.004A9D83.20020802071322@fatcity.com>

I've been reading the thread on DUAL vs X$DUAL, read the referenced article and tried some testing on our system. I do a simple select from DUAL and I get the same statistics as were in the article, but sometimes I also get 1 memory sort. Does anyone know why this would be? And if this is true, that really makes me want to change over to X$DUAL. Also, what is the consensus about creating a view for DUAL that references X$DUAL? I'm running the Oracle Application and cannot change all of their code to use something other than DUAL, and there is a lot of it.

Here are the statistics on the select. Notice the difference between the first vs repeat of the same seelct.

Connected to:
Oracle8i Enterprise Edition Release 8.1.7.1.1 - Production With the Partitioning option
JServer Release 8.1.7.1.1 - Production

SQL> set autotrace traceonly
SQL> select 'y' from dual;

Execution Plan

0 SELECT STATEMENT Optimizer=CHOOSE (Cost=2 Card=1) 1 0 TABLE ACCESS (FULL) OF 'DUAL' (Cost=2 Card=1)

Statistics

          0  recursive calls
          4  db block gets
          1  consistent gets
          0  physical reads
          0  redo size
        361  bytes sent via SQL*Net to client
        425  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          1  sorts (memory)
          0  sorts (disk)
          1  rows processed

SQL> / Execution Plan

0 SELECT STATEMENT Optimizer=CHOOSE (Cost=2 Card=1) 1 0 TABLE ACCESS (FULL) OF 'DUAL' (Cost=2 Card=1)

Statistics

          0  recursive calls
          4  db block gets
          1  consistent gets
          0  physical reads
          0  redo size
        361  bytes sent via SQL*Net to client
        425  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed

SQL> Thanks for your input.

John Zoltak
North American Mfg Co
4455 East 71st Street
Cleveland Ohio 44105

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Received on Fri Aug 02 2002 - 10:13:22 CDT