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Thursday, September 20, 2012

Enabling Oracle Extended SQL Trace by Module and Action

I have written previously about the value of assigning meaningful values to the module and action attributes on a database session (see Using Oracle Enterprise Manager (Grid Control) with PeopleSoft). Oracle added instrumentation to PeopleTools 8.50 (see PeopleTools 8.50 uses DBMS_APPLICATION_INFO to Identify Database Sessions) that sets module and action for on-line and batch sessions.  However, I still use my own trigger to set these attributes for processes initiated by the Process Scheduler.

I originally became interested in module and action because it made it possible to analyse performance problems in specific processes with Active Session History (see Practical Use of ASH). However, since Oracle 10g there is also a very easy way to enable Oracle's extended session trace in the sessions relating to  specific processes.

In the Oracle supplied PL/SQL package DBMS_MONITOR, there are two programs to specify combinations of module and action for which SQL trace will be enabled.  It is rather like setting a watchpoint in a debugger. SERV_MOD_ACT_TRACE_ENABLE is used to create a watchpoint, and SERV_MOD_ACT_TRACE_DISABLE removes it. Trace is then enabled in a session when the module and action is set to a value that matches a watchpoint, and disabled when the module and/or action is changed to a value for which there is no watchpoint.

This screenshot from OEM shows that a query is being run within a PeopleSoft component RECV_PO, page PO_PICK_ORDERS.

It would be a simple matter to have Oracle trace the session for that component by setting a watchpoint.

BEGIN
 sys.dbms_monitor.serv_mod_act_trace_enable
 (service_name=>'P1PPP'
 ,module_name =>'RECV_PO'
 ,waits=>TRUE
 ,binds=>TRUE);
END;
/

Note that the service name must be specified as part of the watchpoint.  This will usually be the same as the PeopleSoft database name.  Thus, watchpoints copied to another database by cloning won't be effective because the service name will be different.

I could also have specified an action in the example above, but I want to trace all pages in the component and the search dialogue.

As with the other programs in dbms_monitor, information on wait events are included in traces by default.  In the above example, I have also requested information on bind variables to be included in the trace.

When setting a SQL trace for an on-line component it is possible that many different users could trigger tracing.  Trace will be enabled and disabled for each user. The result is that you will get a trace file for each application server process, and each trace file might contain the activity for more than one user if the application server process handled more than one service request.

Watchpoints can be removed in a similar way.
BEGIN
 sys.dbms_monitor.serv_mod_act_trace_disable
 (service_name=>'P1PPP'
 ,module_name =>'RECV_PO'
 ,action_name =>'PO_PICK_ORDERS');
END;
/

Watchpoints are held the table SYS.WRI$_TRACING_ENABLED.

SELECT * FROM sys.wri$_tracing_enabled
/

TRACE_TYPE PRIMARY_ID QUALIFIER_ID1 QUALIFIER_ID2   INSTANCE_NAME FLAGS
---------- ---------- ------------- --------------- ------------- -----
         5 P1PPP      RECV_PO       PO_PICK_ORDERS                   12

This technique is also effective for processes initiated by the Process Scheduler. The default behaviour from PeopleTools 8.50 is to set Action to the process name, my trigger sets Module to the process name.
If I specify only the Module in SERV_MOD_ACT_TRACE_ENABLE, then it trace will be enabled for that module and for any action.
BEGIN
 sys.dbms_monitor.serv_mod_act_trace_disable
 (service_name=>'AAAAAAA'
 ,module_name =>'GPPDPRUN');
END;
/
I choose to set the action to the Process Instance number because I find it useful to relate ASH data to a specific batch process. The above screenshot from OEM shows a streamed Global Payroll calculation running with many concurrent GPPDPRUN processes. The watchpoint would cause each and every processes to trace.

However, it has been suggested that if the Action was set to the process run control ID then the watchpoint could be set to the specific run control value used by a user or scheduled job. It would be a simple matter of changing the trigger (I'll leave that as an excercise).  Then, a user could be told to use a specific value for run control ID that would then invoke trace.
BEGIN
 sys.dbms_monitor.serv_mod_act_trace_disable
 (service_name=>'AAAAAAA'
 ,action_name =>'TRACEME');
END;
/

Update 24.11.2012 This technique will not work for Application Engine from PeopleTools 8.52 because it now sets MODULE to a value that includes a session number and so cannot be predicted.

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