OCP-043 SESSION_TRACE_DISABLE

134. In your test database, you find that a user's session is executing a lot of SQL statements, resulting in
the generation of a large number of trace files. While investigating the reason, you find that SQL trace has
been enabled at the instance level.
You want to disable SQL trace, remotely, only for that user session to reduce the volume of trace data
being generated.
How do you achieve this objective?
A.by setting the SQL_TRACE parameter to FALSE in the parameter file

B.by using DBMS_MONITOR.SESSION_TRACE_DISABLE to disable the tracing for the user session
C.by setting the SQL_TRACE parameter to FALSE by using the ALTER SYSTEM command in the user
session
D.by setting the SQL_TRACE parameter to FALSE by using the ALTER SESSION command in the user
session
Answer: B

 Tracing for Session

The SESSION_TRACE_ENABLE procedure enables the trace for a given database session identifier (SID), on the local instance.

To enable tracing for a specific session ID and serial number, determine the values for the session that you want to trace:

SELECT SID, SERIAL#, USERNAME FROM V$SESSION;

       SID    SERIAL# USERNAME
---------- ---------- ------------------------------
        27         60 OE
...

Use the appropriate values to enable tracing for a specific session:

EXECUTE DBMS_MONITOR.SESSION_TRACE_ENABLE(session_id => 27, serial_num => 60,
        waits => TRUE, binds => FALSE);

The TRUE argument specifies that wait information will be present in the trace. The FALSE argument specifies that bind information will not be present in the trace.

The SESSION_TRACE_DISABLE procedure disables the trace for a given database session identifier (SID) and serial number. For example:

EXECUTE DBMS_MONITOR.SESSION_TRACE_DISABLE(session_id => 27, serial_num => 60);

While the DBMS_MONITOR package can only be invoked by a user with the DBA role, any user can also enable SQL tracing for their own session by using theDBMS_SESSION package. The SESSION_TRACE_ENABLE procedure can be invoked by any user to enable session-level SQL trace for their own session. For example:

EXECUTE DBMS_SESSION.SESSION_TRACE_ENABLE(waits => TRUE, binds => FALSE);

The TRUE argument specifies that wait information will be present in the trace. The FALSE argument specifies that bind information will not be present in the trace.

The SESSION_TRACE_DISABLE procedure disables the trace for the invoking session. For example:

EXECUTE DBMS_SESSION.SESSION_TRACE_DISABLE();

 Tracing for Entire Instance or Database

The DATABASE_TRACE_ENABLE procedure enables SQL tracing for a given instance or an entire database. For example:

EXECUTE DBMS_MONITOR.DATABASE_TRACE_ENABLE(waits => TRUE, binds => FALSE, 
        instance_name => 'inst1');

In this example, the inst1 instance is specified to enable tracing for that instance. The TRUE argument specifies that wait information will be present in the trace. The FALSE argument specifies that bind information will not be present in the trace. This example will result in SQL tracing of every SQL in the inst1instance.

The DATABASE_TRACE_ENABLE procedure will override all other session-level traces, but will be complementary to the client identifier, service, module, and action traces. All new sessions will inherit the wait and bind information specified by this procedure until the DATABASE_TRACE_DISABLE procedure is called. When this procedure is invoked with the instance_name parameter specified, it will reset the session-level SQL trace for the named instance. If this procedure is invoked without the instance_name parameter specified, it will reset the session-level SQL trace for the entire database.

The DATABASE_TRACE_DISABLE procedure disables the tracing for an entire instance or database. For example:

EXECUTE DBMS_MONITOR.DATABASE_TRACE_DISABLE(instance_name => 'inst1');

In this example, all session-level SQL tracing will be disabled for the inst1 instance. To disable the session-level SQL tracing for an entire database, invoke theDATABASE_TRACE_DISABLE procedure without specifying the instance_name parameter:

EXECUTE DBMS_MONITOR.DATABASE_TRACE_DISABLE();

 Enabling the SQL Trace Facility

Enable the SQL Trace facility for the session by using one of the following:

• DBMS_SESSION.SET_SQL_TRACE procedure

• ALTER SESSION SET SQL_TRACE = TRUE;

  Caution:

  Because running the SQL Trace facility increases system overhead, enable it only when tuning SQL statements, and disable it when you are finished. It is recommended that you use the DBMS_SESSION or DBMS_MONITOR packages to enable SQL tracing for a session or an instance instead. For more information on using these packages, see  "Enabling and Disabling for End to End Tracing".

  You might need to modify an application to contain the ALTER SESSION statement. For example, to issue the ALTER SESSION statement in Oracle Forms, invoke Oracle Forms using the -s option, or invoke Oracle Forms (Design) using the statistics option. For more information on Oracle Forms, see theOracle Forms Reference.

To disable the SQL Trace facility for the session, enter:

ALTER SESSION SET SQL_TRACE = FALSE;

The SQL Trace facility is automatically disabled for the session when the application disconnects from Oracle.

You can enable the SQL Trace facility for an instance by setting the value of the SQL_TRACE initialization parameter to TRUE in the initialization file.

SQL_TRACE = TRUE

After the instance has been restarted with the updated initialization parameter file, SQL Trace is enabled for the instance and statistics are collected for all sessions. If the SQL Trace facility has been enabled for the instance, you can disable it for the instance by setting the value of the SQL_TRACE parameter toFALSE.

Note:

Setting  SQL_TRACE to TRUE can have a severe performance impact.

 DBMS_MONITOR

The DBMS_MONITOR package let you use PL/SQL for controlling additional tracing and statistics gathering.

The chapter contains the following topics:

• Summary of DBMS_MONITOR Subprograms

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Summary of DBMS_MONITOR Subprograms

Table 60-1 DBMS_MONITOR Package Subprograms

Subprogram	Description
CLIENT_ID_STAT_DISABLE Procedure	Disables statistic gathering previously enabled for a given Client Identifier
CLIENT_ID_STAT_ENABLE Procedure	Enables statistic gathering for a given Client Identifier
CLIENT_ID_TRACE_DISABLE Procedure	Disables the trace previously enabled for a given Client Identifier globally for the database
CLIENT_ID_TRACE_ENABLE Procedure	Enables the trace for a given Client Identifier globally for the database
DATABASE_TRACE_DISABLE Procedure	Disables SQL trace for the whole database or a specific instance
DATABASE_TRACE_ENABLE Procedure	Enables SQL trace for the whole database or a specific instance
SERV_MOD_ACT_STAT_DISABLE Procedure	Disables statistic gathering enabled for a given combination of Service Name, MODULE and ACTION
SERV_MOD_ACT_STAT_ENABLE Procedure	Enables statistic gathering for a given combination of Service Name, MODULE and ACTION
SERV_MOD_ACT_TRACE_DISABLE Procedure	Disables the trace for ALL enabled instances for a or a given combination of Service Name, MODULE and ACTIONname globally
SERV_MOD_ACT_TRACE_ENABLE Procedure	Enables SQL tracing for a given combination of Service Name, MODULE and ACTION globally unless an instance_name is specified
SESSION_TRACE_DISABLE Procedure	Disables the previously enabled trace for a given database session identifier (SID) on the local instance
SESSION_TRACE_ENABLE Procedure	Enables the trace for a given database session identifier (SID) on the local instance

SESSION_TRACE_DISABLE Procedure

This procedure will disable the trace for a given database session at the local instance.

Syntax

DBMS_MONITOR.SESSION_TRACE_DISABLE(
   session_id      IN     BINARY_INTEGER DEFAULT NULL,
   serial_num      IN     BINARY_INTEGER DEFAULT NULL);

Parameters

Table 60-12 SESSION_TRACE_DISABLE Procedure Parameters

Parameter	Description
session_id	Name of the service for which SQL trace is disabled.
serial_num	Serial number for this session.

Usage Notes

If serial_num is NULL but session_id is specified, a session with a given session_id is no longer traced irrespective of its serial number. If both session_id andserial_num are NULL, the current user session is no longer traced. It is illegal to specify NULL session_id and non-NULL serial_num. In addition, the NULL values are default and can be omitted.

Examples

To enable tracing for a client with a given client session ID:

EXECUTE DBMS_MONITOR.SESSION_TRACE_ENABLE(7,4634, TRUE, FALSE);

To disable tracing specified in the previous step:

EXECUTE DBMS_MONITOR.SESSION_TRACE_DISABLE(7,4634);;

---

SESSION_TRACE_ENABLE Procedure

This procedure enables a SQL trace for the given Session ID on the local instance

Syntax

DBMS_MONITOR.SESSION_TRACE_ENABLE(
    session_id   IN  BINARY_INTEGER DEFAULT NULL,
    serial_num   IN  BINARY_INTEGER DEFAULT NULL,
    waits        IN  BOOLEAN DEFAULT TRUE,
    binds        IN  BOOLEAN DEFAULT FALSE)

Parameters

Table 60-13 SESSION_TRACE_ENABLE Procedure Parameters

Parameter	Description
session_id	Database Session Identifier for which SQL tracing is enabled. Specifying NULL means that my current session should be traced.
serial_num	Serial number for this session. Specifying NULL means that any session which matches session_id (irrespective of serial number) should be traced.
waits	If TRUE, wait information is present in the trace.
binds	If TRUE, bind information is present in the trace.

Usage Notes

The procedure enables a trace for a given database session, and is still useful for client/server applications. The trace is enabled only on the instance to which the caller is connected, since database sessions do not span instances. This tracing is strictly local to an instance.

If serial_num is NULL but session_id is specified, a session with a given session_id is traced irrespective of its serial number. If both session_id and serial_numare NULL, the current user session is traced. It is illegal to specify NULL session_id and non-NULL serial_num. In addition, the NULL values are default and can be omitted.

Examples

To enable tracing for a client with a given client session ID:

EXECUTE DBMS_MONITOR.SESSION_TRACE_ENABLE(7,4634, TRUE, FALSE);

To disable tracing specified in the previous step:

EXECUTE DBMS_MONITOR.SESSION_TRACE_DISABLE(7,4634);

Either

EXECUTE DBMS_MONITOR.SESSION_TRACE_ENABLE(5);

or

EXECUTE DBMS_MONITOR.SESSION_TRACE_ENABLE(5, NULL);

traces the session with session ID of 5, while either

EXECUTE DBMS_MONITOR.SESSION_TRACE_ENABLE();

or

EXECUTE DBMS_MONITOR.SESSION_TRACE_ENABLE(NULL, NULL);

traces the current user session. Also,

EXECUTE DBMS_MONITOR.SESSION_TRACE_ENABLE(NULL, NULL, TRUE, TRUE);

traces the current user session including waits and binds. The same can be also expressed using keyword syntax:

EXECUTE DBMS_MONITOR.SESSION_TRACE_ENABLE(binds=>TRUE);