Oracle Autotrace tips

Oracle Database Tips by Donald Burleson

The autotrace utility is a very underutilized feature of SQL*Plus. It offers statement tracing and instant feedback on any successful SELECT, INSERT, UPDATE or DELETE statement.

The autotrace provides instantaneous feedback including the returned rows, execution plan, and statistics. The user doesn't need to be concerned about trace file locations and formatting since the output is displayed instantly on the screen. This is very important data that can be used to tune the SQL statement.

Oracle autotrace supports the following options:

• autotrace on - Enables all options.

• autotrace on explain - Displays returned rows and the explain plan.

• autotrace on statistics - Displays returned rows and statistics.

• autotrace trace explain - Displays the execution plan for a select statement without actually executing it. "set autotrace trace explain"

• autotrace traceonly - Displays execution plan and statistics without displaying the returned rows. This option should be used when a large result set is expected.

Oracle autotrace is so easy to use that it should be the first tracing utility used for most SQL performance tuning issues. tkprof can be used for more detailed analysis.

Oracle Autotrace session

For any specific SQL query you can see SQL execution performance statistics. In SQL*Plus you can issue the "set autotrace" command and then issue your SQL statement:

SQL> set autotrace traceonly explain
SQL> select ename from emp where empno = 12;

Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE
1 0 TABLE ACCESS (BY INDEX ROWID) OF 'EMP'
2 1 INDEX (UNIQUE SCAN) OF 'PK_EMP' (UNIQUE)

Statistics
----------------------------------------------------------
83 recursive calls
0 db block gets
21 consistent gets
3 physical reads
0 redo size
221 bytes sent via SQL*Net to client
368 bytes received via SQL*Net from client
1 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
0 rows processed

Also see these extra notes on autotrace:

- Learn Oracle autotrace functions
- SQL Execution Plans - autotrace feature of SQL*Plus - Explain Plan
- Using SQL*Plus autotrace
- Oracle Utilities autotrace utility
- autotrace command
- SQL*Plus AUTOTRACE plustrc tips
- Techniques Tuning Performance Explain Plan

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