21 Database Replay

21.1.1 Workload Capture

The first step in using Database Replay is to capture the production workload. Capturing a workload involves recording all requests made by external clients to Oracle Database. When workload capture is enabled, all external client requests directed to Oracle Database are tracked and stored in binary files, called capture files, on the file system. These capture files are platform independent and can be transported to another system. You can specify the start time and duration for the workload capture, as well as the location to store the capture files. Once workload capture begins, all external database calls are written to the capture files. The capture files contain all relevant information about the client request, such as SQL text, bind values, and transaction information. Background activities and database scheduler jobs are not captured.

For information about how to capture a workload on the production system, see "Capturing a Database Workload".

21.1.2 Workload Preprocessing

Once the workload has been captured, the information in the capture files need to be preprocessed. Preprocessing creates all necessary metadata needed for replaying the workload. This must be done once for every captured workload before they can be replayed. After the captured workload is preprocessed, it can be replayed repeatedly on a replay system running the same version of Oracle Database. Typically, the capture files should be copied to another system for preprocessing. As workload preprocessing can be time consuming and resource intensive, it is recommended that this step be performed on the test system where the workload will be replayed.

21.1.3 Workload Replay

After a captured workload has been preprocessed, it can be replayed on a test system. During the workload replay phase, Oracle Database performs the actions recorded during the workload capture phase on the test system by recreating all captured external client requests with the same timing, concurrency, and transaction dependencies of the production system.

Database Replay uses a client program called the replay client to recreate all external client requests recorded during workload capture. Depending on the captured workload, you may need one or more replay clients to properly replay the workload. A calibration tool is provided to help determine the number of replay clients needed for a particular workload. Because the entire workload is replayed, including DML and SQL queries, the data in the replay system should be logically similar to the data in the capture system to minimize data divergence and enable reliable analysis of the replay.

21.1.4 Analysis and Reporting

Once the workload is replayed, in-depth reporting is provided for you to perform detailed analysis of both workload capture and replay.

The report summary provides basic information about the workload capture and replay, such as errors encountered during replay and data divergence in rows returned by DML or SQL queries. A comparison of several statistics—such as DB time, average active sessions, and user calls—between the workload capture and the workload replay is also provided. For advanced analysis, Automatic Workload Repository (AWR) reports are available to enable detailed comparison of performance statistics between the workload capture and the workload replay. The information available in these reports is very detailed, and some differences between the workload capture and replay can be expected.

For application-level validation, you should consider developing a script to assess the overall success of the replay. For example, if 10,000 orders are processed during workload capture, you should validate that similar number of orders are also processed during replay.

For information about how to generate and analyze workload capture reports, see "Analyzing Workload Capture".

21.2.1 Enabling and Disabling Workload Capture

Before a workload can be captured, workload capture needs to be enabled on the system where you plan to capture the workload. By default, workload capture is not enabled in Oracle Database 10g Release 2 (10.2). You can enable or disable workload capture by specifying the PRE_11G_ENABLE_CAPTURE initialization parameter.

To enable workload capture, run the wrrenbl.sql script at the SQL prompt:

@$ORACLE_HOME/rdbms/admin/wrrenbl.sql

The wrrenbl.sql script calls the ALTER SYSTEM SQL statement to set the PRE_11G_ENABLE_CAPTURE initialization parameter to TRUE. If a server parameter file (spfile) is being used, the PRE_11G_ENABLE_CAPTURE initialization parameter will be modified for the currently running instance and recorded in the spfile, so that the new setting will persist when the database is restarted. If a spfile is not being used, the PRE_11G_ENABLE_CAPTURE initialization parameter will only be modified for the currently running instance, and the new setting will not persist when the database is restarted. To make the setting persistent without using a spfile, you will need to manually specify the parameter in the initialization parameter file (init.ora).

To disable workload capture, run the wrrdsbl.sql script at the SQL prompt:

@$ORACLE_HOME/rdbms/admin/wrrdsbl.sql

The wrrdsbl.sql script calls the ALTER SYSTEM SQL statement to set the PRE_11G_ENABLE_CAPTURE initialization parameter to FALSE. If a server parameter file (spfile) is being used, the PRE_11G_ENABLE_CAPTURE initialization parameter will be modified for the currently running instance and also recorded in the spfile, so that the new setting will persist when the database is restarted. If a spfile is not being used, the PRE_11G_ENABLE_CAPTURE initialization parameter will only be modified for the currently running instance, and the new setting will not persist when the database is restarted. To make the setting persistent without using a spfile, you will need to manually specify the parameter in the initialization parameter file (init.ora).

21.2.2 Prerequisites for Capturing a Database Workload

Before starting a workload capture, you should have a strategy in place to restore the database on the test system. Before a workload can be replayed, the state of the application data on the replay system should be similar to that of the capture system when replay begins. To accomplish this, consider using one of the following methods:

• Recovery Manager (RMAN) DUPLICATE command

• Snapshot standby

• Data Pump Import and Export

This will allow you to restore the database on the replay system to the application state as of the workload capture start time.

21.2.3 Workload Capture Options

Proper planning before workload capture is required to ensure that the capture will be accurate and useful when replayed in another environment.

Before capturing a database workload, carefully consider the following options:

• Restarting the Database

• Defining the Workload Filters

• Setting Up the Capture Directory

21.2.4 Workload Capture Restrictions

The following types of client requests are not captured in a workload in the current release:

• Direct path load of data from external files using utilities such as SQL*Loader

• Shared server requests (Oracle MTS)

• Oracle Streams

• Advanced Replication streams

• Non-PL/SQL based Advanced Queuing (AQ)

• Flashback queries

• Oracle Call Interface (OCI) based object navigations

• Non SQL-based object access

• Distributed transactions (any distributed transactions that are captured will be replayed as local transactions)

• Remote DESCRIBE and COMMIT operations

21.2.5 Capturing a Database Workload Using Enterprise Manager

This section describes how to capture a database workload using Enterprise Manager.

To capture a database workload using Enterprise Manager:

1. On the Administration page, under Real Application Testing, click Database Replay.

   The Database Replay page appears.

2. In the Go to Task column, click the icon that corresponds to the Capture Workload task.

   The Capture Workload: Plan Environment page appears.

3. Verify that all prerequisites are met before proceeding.

   For information about the prerequisites, see "Prerequisites for Capturing a Database Workload". For each verified prerequisite, check the box in the Acknowledge column. Once all prerequisites are verified, click Next.

   The Capture Workload: Options page appears.

4. Select the workload capture options.

   • Under Database Restart Options, select whether the database will be restarted before workload capture.

     It is strongly recommended that the database be restarted before capturing a workload to enable a clean state for workload capture. Otherwise, potential problems may arise when replaying the workload. For more information, see "Restarting the Database".

   • Under Workload Filters, select whether to use exclusion filters by selecting Exclusion in the Filter Mode list, or inclusion filters by selecting Inclusion in the Filter Mode list.

     To add filters, click Add Another Row and enter the filter name, session attribute type, and attribute value in the corresponding fields. For more information, see "Defining the Workload Filters".

   After selecting the desired workload capture options, click Next. The Capture Workload: Parameters page appears.

5. Define the parameters for the workload capture.

   • Under Workload Capture Parameters, in the Capture Name field, enter a name for the workload capture. In the Directory Object list, select the directory where the captured workload will be stored. You must select a directory that does not already contain a workload capture. For more information, see "Setting Up the Capture Directory".

     To create a new directory object, click Create Directory Object. The Create Directory Object page appears. In the Name field, enter a name for the directory object. In the Path field, enter the path to the directory object. To test if the directory exists in the file system, click Test File System. If the directory does not exist, it will need to be created first.

   • Under Database Shutdown Parameters, select the type of database shutdown method to perform. This option only appears if the database will be restarted before workload capture. The types of available database shutdown methods include:

     • Immediate

       An immediate shutdown will roll back all active transactions and disconnect all connected users prior to shutting down the database.

     • Transactional

       A transactional shutdown will first complete all active transactions and then disconnect the connected user prior to shutting down the database.

     • Abort

       An abort shutdown will shut down the database instantaneously by aborting all active transactions.

   • Under Database Startup Parameters, select if the database will restart using the current default server parameter file (spfile) or a specific parameter file (pfile). To select a pfile, enter the fully qualified name for the pfile. This option only appears if the database will be restarted before workload capture.

   After defining the parameters for the workload capture, click Next. The Capture Workload: Schedule page appears.

6. Under Job Parameters, define the parameters for the job:

   • In the Job Name field, enter a name for the job name or accept the system generated name.

   • In the Description field, enter an optional description of the job.

7. Under Job Schedule, specify a start time and duration for the workload capture:

   • Under Start, select whether the job will run immediately by selecting Immediately, or at a later time by selecting Later and specifying the desired time using the Date and Time fields.

   • Under Capture Duration, specify how long the job will run by selecting Duration and specifying the desired duration using the Hours and Minutes fields. To not specify a capture duration, select Not Specified. If a capture duration is unspecified, the job must be stopped manually.

8. Under Job Credentials, enter the host and database login credentials:

   • Under Host Credentials, enter the username and password for the host system.

   • Under Database Credentials, enter the username and password for the database that will used for the workload capture. The user needs the DBA privilege in order to capture the workload.

   Click Next. The Capture Workload: Review page appears.

9. Review the job settings for the workload capture that have been defined. To run the job, click Submit. To make changes, click Back. To cancel the workload capture without saving changes, click Cancel.

10. Depending on the job settings that have been defined:

    • If the job is scheduled to start immediately and the database will be restarted, the Confirmation: Restart Database page appears. To restart the database, click Yes. The Information: Restart Database page appears while the database is being restarted. Once the database is restarted, the workload capture begins automatically. Click Refresh. The View Workload Capture page appears.

    • If the job is scheduled to start immediately but the database will not be restarted, the workload capture begins automatically and the Database Replay page appears with a confirmation that the job has been successfully created.

    • If the job is scheduled to start at a later time, the Database Replay page appears with a confirmation that the job has been successfully created.

    Once workload capture begins, you can monitor the capture process using the View Workload Capture page, as described in "Monitoring an Active Workload Capture".

21.2.6 Monitoring Workload Capture Using Enterprise Manager

This section describes how to monitor workload capture using Enterprise Manager. The primary tool for monitoring workload capture is Oracle Enterprise Manager. Using Enterprise Manager, you can:

• Monitor or stop an active workload capture

• View or delete a completed workload capture

If for some reason Oracle Enterprise Manager is unavailable, you can monitor workload capture using views, as described in "Monitoring Workload Capture Using Views".

This section contains the following topics:

• Monitoring an Active Workload Capture

• Stopping an Active Workload Capture

• Managing a Completed Workload Capture

21.2.7 Capturing a Database Workload Using APIs

This section describes how to capture a database workload using APIs. Capturing a database workload using the DBMS_WORKLOAD_CAPTURE package involves:

• Adding and Removing Workload Filters

• Starting a Workload Capture

• Stopping a Workload Capture

• Exporting AWR Data for Workload Capture

BEGIN
  DBMS_WORKLOAD_CAPTURE.ADD_FILTER (
                           fname => 'user_ichan',
                           fattribute => 'USER',
                           fvalue => 'ICHAN');
END;
/

BEGIN
  DBMS_WORKLOAD_CAPTURE.DELETE_FILTER (fname => 'user_ichan');
END;
/

BEGIN
  DBMS_WORKLOAD_CAPTURE.START_CAPTURE (name => 'dec06_peak', 
                           dir => 'dec06',
                           duration => 600);
END;
/

BEGIN
  DBMS_WORKLOAD_CAPTURE.FINISH_CAPTURE (); 
END;
/

BEGIN
  DBMS_WORKLOAD_CAPTURE.EXPORT_AWR (capture_id => 2);
END;
/

21.2.8 Monitoring Workload Capture Using Views

This section summarizes the views that you can display to monitor workload capture. You need DBA privileges to access these views.

• The DBA_WORKLOAD_CAPTURES view lists all the workload captures that have been captured in the current database.

• The DBA_WORKLOAD_FILTERS view lists all workload filters used for workload captures defined in the current database.

21.3.1 Generating a Workload Capture Report Using Enterprise Manager

The workload capture report contains captured workload statistics, information about the top session activities that were captured, and any workload filters used during the capture process.

To generate a workload capture report using Enterprise Manager:

1. On the Administration page, under Real Application Testing, click Database Replay.

   The Database Replay page appears.

2. Click View Workload Capture History.

   The View Workload Capture History page appears.

3. Select the workload capture for which you want to run a workload capture report and click View.

   The View Workload Capture page appears.

4. To view the workload capture report, click View Workload Capture Report.

   The Report window opens while the report is being generated.

5. Once the report is generated, you can save the report by clicking Save to File.

   For information about how to use a workload capture report, see "Using a Workload Capture Report".

21.3.2 Generating a Workload Capture Report Using APIs

The workload capture report contains captured workload statistics, information about the top session activities that were captured, and any workload filters used during the capture process.

To generate a report on the latest workload capture, use the DBMS_WORKLOAD_CAPTURE.GET_CAPTURE_INFO procedure and the DBMS_WORKLOAD_CAPTURE.REPORT function:

DECLARE
  cap_id         NUMBER;
  cap_rpt        CLOB;
BEGIN
  cap_id  := DBMS_WORKLOAD_CAPTURE.GET_CAPTURE_INFO(dir => 'dec06');
  cap_rpt := DBMS_WORKLOAD_CAPTURE.REPORT(capture_id => cap_id,
                           format => DBMS_WORKLOAD_CAPTURE.TYPE_TEXT);
END;
/

In this example, the GET_CAPTURE_INFO procedure retrieves all information regarding the workload capture in the dec06 directory and returns the appropriate cap_id for the workload capture. The REPORT function generates a text report using the cap_id that was returned by the GET_CAPTURE_INFO procedure.

The GET_CAPTURE_INFO procedure uses the dir required parameter, which specifies the name of the workload capture directory object.

The REPORT function uses the following parameters:

• The capture_id required parameter relates to the directory that contains the workload capture for which the report will be generated. The directory should be a valid directory in the host system containing the workload capture. The value of this parameter should match the cap_id returned by the GET_CAPTURE_INFO procedure.

• The format parameter required parameter specifies the report format. Valid values include DBMS_WORKLOAD_CAPTURE.TYPE_TEXT and DBMS_WORKLOAD_REPLAY.TYPE_HTML.

For information about how to use a workload capture report, see "Using a Workload Capture Report".

21.3.3 Using a Workload Capture Report

The workload capture report contains various types of information that can be used to assess the validity of the workload capture. Using the information provided in this report, you can determine if the captured workload:

• Represents the actual workload you want to replay

• Does not contain any workload you want to exclude

• Can be replayed

The information contained in the workload capture report are divided into the following categories:

• Details about the workload capture (such as the name of the workload capture, defined filters, date, time, and SCN of capture)

• Overall statistics about the workload capture (such as the total DB time captured, and the number of logins and transactions captured) and the corresponding percentages with respect to total system activity

• Profile of the captured workload

• Profile of the workload that was not captured due to version limitations

• Profile of the uncaptured workload that were excluded using defined filters

• Profile of the uncaptured workload that consists of background process or scheduled jobs