Sunday, September 30, 2012

Maintaining Optimizer Statistics on PeopleSoft on Oracle 11g

I have been considering how to collect optimizer statistics for a PeopleSoft system running on an Oracle 11g database.  Despite 11g being several years old, most of my current customers are still using 10g, though some are looking at the upgrade to 11g.  I believe a slightly different approach is required.

In 2009, I wrote a series of blog postings on the subject of collecting statistics.  However these were all based on Oracle 10g.  I proposed a PL/SQL package that would use meta-data in a database table to determine how to collect statistics on a table, or deliberate supress collection of statistics.
I also recommended that statistics on tables created for use as temporary records in Application Engine programs should have their statistics deleted and locked  to prevent system-wide jobs refreshing their statistics. I proposed a package that collected statistics according to meta-data defined in a table.

IN 2011, Oracle published document 1322888.1 “pscbo_stats - Improving Statistics in Oracle RDBMS for PeopleSoft Enterprise”.  It takes a similar approach to my 10g package.  A PL/SQL package is used to collect statistics.  A number of tables control whether, when and how statistics are collected on each record.  Oracle's package is also intended to be used to collect schema-wide statistics.

The psbo_stats package is a attempt to solve a genuine problem, and it has continued to evolve since its initial release.  However, I have a number of objections to it.
  • You are expected to replace the default automatic jobs that collect statistics with pscbo_stats, so it is a move away from standard default maintenance procedures.
  • pscbo_stats is still fundamentally a 10g solution. It does not use 11g table preferences.
  • It does use the Oracle automatic sample size in 11g if histograms are not to be collected.  Otherwise, it defaults to the previous behaviour of either using 100% sample size for when called by %UpdateStats with the ‘high’ sample size, or a variety of fixed sample sizes based on internal rules and the number of rows in the table.
  • The package contains a procedure that collects statistics on all objects in the schema that also refreshes statistics that are not stale but which have not been refreshed for a period of time determined by the size of the table. 
  • When it collects histograms it always sets the maximum bucket size of 254. This may not always be desirable for height balanced histograms.
  • There is no support for collecting aggregated or incremental statistics on partitioned objects.
I think that the 11g table preferences offer better control over collection of statistics.

Oracle considerably enhanced the delivered DBMS_STATS package in 11g.  It became possible to specify default values for parameters in the dbms_stats.gather_table_stats program for for each table.

The guiding principle in 11g, and one that is not specific to PeopleSoft, is that instead of calling dbms_stats.gather_table_stats with the desired parameters, we should set table preferences with the desired parameters and then just call dbms_stats without table specific parameters. We can then just leave the default database and schema-wide procedures get on with the job of collecting statistics.    

A document that describes the updated approach and the various scripts are available on the Go-Faster website at http://www.go-faster.co.uk/docs.htm#Managing.Statistics.11g.

CAVEAT: This document represents some experimental work that is in progress.  It has not been tested against a customer system, let alone been used in production. I would welcome any feedback, and the opportunity to work with someone on a PeopleSoft system on Oracle 11g.

Update 4.2.2015: I have put this solution into PeopleSoft systems at two customer systems last year, so it is no longer just theory.

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.