Understanding Correlation

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Understanding Correlation In HP LoadRunner
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Correlation

• What is correlation
• Types of Correlation
• Automatic Correlation
• Manual Correlation

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What is Correlation

• Sometime, after creating a script, a simple
  playback fail even though the recording of the
  same actions succeeded.
• Many applications use dynamic values that change
  each time you use the application. For example,
  some servers assign a unique session ID for every
  new session. When you try to replay a recorded
  session, the application creates a new session ID
  that differs from the recorded session ID.
• LoadRunner addresses this issue through
  correlation. Correlation saves the changing
  values to a parameter.
• When running the emulation, the Vuser does not
  use the recorded valueinstead, it uses the new
  value assigned to it by the server.

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Automatic Correlation

• Open HP Web Tours.
• Select Start gt Programs gt LoadRunner gt Samples gt
  Web gt HP Web Tours Application. A browser opens
  with the HP Web Tours home page.
• Click the administration link on the HP Web Tours
  home page. The administration page opens.
• Select the 3rd checkbox entitled Set LOGIN
  form's action tag to an error page.
• Scroll down to the bottom of the page and click
  Update.
• Scroll down to the bottom of the page and click
  the Return to the Web Tours Homepage link.
• This setting tells the server not to allow
  duplicate session IDs.
• Close the browser.

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Automatic Correlation

• In the modified configuration of HP Web Tours,
  the server assigns a unique session ID to the
  Vuser. If you try to play back the script, it
  will fail.
• To overcome this issue, you use VuGen to
  automatically detect the need to correlate the
  session ID.
• After you run the script, VuGen prompts you to
  scan the script for correlations.

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Automatic Correlation

• You will instruct VuGen to insert a step that
  saves the original session ID to a parameter. In
  each replay session, VuGen saves the new unique
  session ID to a parameter. In the subsequent
  steps, it uses the saved value instead of the
  originally recorded value.
• Record a new script with the same steps that you
  recorded previously and save the script as
  Basic_Tutorial_Cor.
• Click Verify Replay in the Task Pane and click
  the Start Replay button at the bottom of the
  instruction pane. VuGen runs the new script. You
  may notice several error messages in the Replay
  Log tab in the Output window, indicated by the
  red-colored text.
• Click Verify Replay in the Task Pane to view the
  Last Replay Summary.

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Automatic Correlation

• Click the link Show and resolve dynamic server
  values in the instruction pane under the heading
  Dynamic Server Values.
• VuGen scans the script, searching for differences
  between the recorded values and the playback
  values.
• VuGen displays a list of these differences that
  may require correlation in the Correlation
  Results tab in the Output window.
• Select the first entry in the Correlation Results
  tab, and click Correlate.

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Automatic Correlation

• VuGen inserts a new step at the top of the script
  saving the original session ID to a parameter.
• In each replay session, VuGen saves the new
  unique session ID to a parameter.
• In the subsequent steps, it uses the saved value
  instead of the originally recorded value.
• Select View gt Tree View to view this new step in
  the test tree.

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Automatic Correlation

• View gt Script View to view the correlation
  statement in the script.
• This statement means Check the server response
  for data located between the following two
  strings
• Left boundary userSession value
• Right boundary gt
• The statement instructs VuGen to save the first
  occurrence of this data to a parameter called
  WCSParam_Diff1.

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Automatic Correlation

• Select Vuser gt Run to replay the script again.
  When the replay ends, select View gt Tree View.
• Look in the Replay Log tab. Note that VuGen no
  longer issues the red-colored error messages.

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Automatic Correlation

• In the script, right-click Service Reg Save
  Param and select Go to step in Replay Log. VuGen
  places the cursor at the corresponding line in
  the replay log.
• The log indicates that function
  web_reg_save_param succeeded, indicating that the
  correlation worked.

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Manual Correlation

• Record a new script with the same steps that you
  recorded previously and save the script as
  Manual_Cor_1.
• Record another script using the same steps as
  above and save the script as Manual_Cor_2.
• Now for script Manual_Cor_2, click on Tools gt
  Compare with script option and select
  Manual_Cor_1 script to compare with.
• Notice that a WDiff window is displayed, showing
  both the scripts and the differences in recording
  are highlighted in yellow color.

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Manual Correlation
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Manual Correlation

• Notice that there is a difference in the
  userSession value in both the scripts.
• Navigate to Script view and add the following
  line to the code
• web_reg_save_param("myval", "LBuserSession
  value", "RBgt", LAST )
• Now search for the userSession value and replace
  the hard-coded valye by parameter as myval
• Replay the script and notice that it plays back
  successfully.

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Manual Correlation
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Questions - To Review Your Skills

• What is correlation and why is it done?
• Perform Automatic correlation on the script.
• Perform Manual correlation on the script.

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Thank You
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