12 Debugging an Application

About Tuning Performance

For applications having a large number of concurrent users, maintaining optimal performance is critical. To optimize your application's performance, remember to utilize the following features:

• Use bind variables within your application whenever possible. You can reference session state values using bind variable syntax in SQL queries and application logic such as PL/SQL executed from processes and validations. Accessing session state using bind variables is the most efficient way to reference session state.

• Include a #TIMING# substitution string in the region footer so that you can view the timing of each region.

Reviewing Session State

Many applications are based on data contained within application controls. For example, buttons can display conditionally based on a value stored in session state. You can view current session state for your application by clicking the Session link on the Developer Toolbar.

Accessing Debug Mode

Viewing a page in Debug Mode enables you to track what the Application Express engine is doing as it renders a page. You access Debug mode by clicking the Debug link in the Developer Toolbar.

Debug Mode displays time codes that correspond to specific Application Express engine actions. This can be useful to determine when the engine is setting session state. The Debug view also shows additional details about item names and computation and processing points. To exit Debug mode, click No Debug on the Developer Toolbar.

You can also use f?p syntax to run an application in Debug mode. Simply call the page and set the Debug argument to YES. For example:

f?p=100:1:&APP_SESSION.::YES

Enabling SQL Tracing and Using TKPROF

Tracing your session can be a very effective way to debug an application. From a database perspective, each page request is a single database session. If you enable SQL tracing, then Oracle Application Express creates a temporary file you can then analyze using the TKPROF utility.

You enable SQL tracing in Oracle Application Express by using f?p syntax to set the argument p_trace=YES. For example, to trace the display of page 1 in application 100, you would use the syntax:

http:/.../f?p=100:1&p_trace=YES

To use the TKPROF utility:

1. Log in to SQL*Plus as a privileged user.

2. Execute the following statement:

   show parameter USER_DUMP_DEST
   

3. Navigate to the directory in which the trace file is created.

4. Run the TKPROF utility from the operating system prompt using the following syntax:

   tkprof filename1 filename2 [waits=yes|no] [sort=option] [print=n]
       [aggregate=yes|no] [insert=filename3] [sys=yes|no] [table=schema.table]
       [explain=user/password] [record=filename4] [width=n]
   

   The input and output files are the only required arguments.

5. To view online Help, invoke TKPROF without arguments.

Monitoring Application and Page Resource Use

Oracle Application Express facilitates the monitoring of resources used by applications and pages by calling the package DBMS_APPLICATION_INFO. Whenever the Application Express engine renders or processes a page, the module is set to APEX and includes the application ID and page number. Once set, you can query the V$SESSION and V$SQLAREA views to monitor transactions.

Viewing Reports

When isolating an issue within a page, it is important to clearly understand the functions it is performing. To accomplish this goal, Application Builder includes a number of page and application reports.

Viewing Page Reports

To view page reports:

1. Navigate to the appropriate Page Definition. See "Accessing a Page Definition".

2. Click one of the following buttons at the top of the Page Definition:

   • Events links to a report that details currently defined page controls and processes. See "About Page Events".

   • Objects displays a list of database objects referenced by the current page. See "About Database Object Dependencies".

   • History displays a history of recently changed pages. See "About History".

Viewing Application Reports

To view application reports:

1. On the Workspace home page, click the Application Builder icon.

2. Select an application.

3. On the Tasks list, click Application Reports.

4. Select the type of reports to view:

   • Shared Components reports offer information on common elements that can display on every page within an application. Reports are grouped by category including Logic, Navigation, Security, User Interface, Globalization, and Files. Report examples include Application Items, Computations, Breadcrumb Entries, Authentication Schemes, and Shortcuts.

   • Page Components reports offer detailed information on controls and logic that execute when the page is rendered (for example, branches, buttons, computations, items, and regions).

   • Activity Reports offer details about developer activity within the current application. Available reports include Changes by Developer, Changes by Developer by Day, Chart of Changes by Developer, Page Performance, and Recent Changes.

   • Cross Application Reports offer information that apply to multiple applications. Available reports include Application Attributes, Application Comments, Build Options, Build Status and Application Status, Page Component Counts, Security Profiles, Authentication Schemes, and Template Defaults by Application.

Debugging Problematic SQL Queries

If your query does not seem to be running correctly, try running it in SQL*Plus, SQL Developer, or in SQL Commands. Any of these approaches will test your query outside the context of your application, making it easier to determine what the problem is.

Removing Controls and Components to Isolate a Problem

If you have problems running a page, try removing controls and components one at a time. Using this approach, you can quickly determine which control or component may be the source of your problem. You can disable a control or component by selecting the Condition attribute Never.

To remove a control or component using conditional attributes:

1. Navigate to the appropriate Page Definition. See "Accessing a Page Definition".

2. Select the name of the control or component you want to disable.

   The appropriate attributes page appears.

3. Scroll down to Condition Type and select Never from the Condition Type list.

4. Click Apply Changes and return to the Page Definition.

5. Try running the page again.

6. Continue to remove controls or components until the page runs correctly.