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# Data assignment methods for parameters

This topic describes the data assignment and update methods for file-type parameters.

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## Data assignment methods for file-type parameters

When using File type parameters, a data file contains the parameter values that are assigned to the Vusers during script run. You can specify the way in which you assign data from the source to the parameters using the following methods.

Assignment Method | Description
--- | ---
Sequential | Assigns data to a Vuser sequentially. As a running Vuser accesses the data table, it takes the next available row of data. If there are not enough values in the data table, parameters are returned to the first value in the table, continuing in a loop until the end of the test.
Random | Assigns a value from a random row in the data table every time a new parameter value is requested. You can specify a seed number for random sequencing. Each seed value represents one sequence of random values used for the test run. Whenever you use this seed value, the same sequence of values is assigned to the Vusers in the scenario. You enable this option if you discover a problem in the test run and want to repeat the test using the same sequence of random values.
Unique | Allocates a unique block of parameter values to each Vuser in the performance test, and then sequentially assigns values to the parameter for each Vuser from within the Vuser's block of values. Ensure that there is enough data in the table for all Vusers and their iterations. If you have 20 Vusers and you want to perform 5 iterations, your table must contain at least 100 unique values. Note: If you use Network Virtualization Insights to analyze test results, several additional Vusers are created, in addition to the Vusers that you defined in the scenario scheduler. Therefore, if the scenario includes a parameter that is assigned values using the unique data assignment method, make sure that the list of parameter values contains several extra values (more than is required by all Vusers to run all their iterations) to accommodate the additional Vusers. If you run out of unique values, it behaves according to the option you select in the When out of values box. For details on the different data assignment and update methods, see Data assignment and update methods for file parameters.

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## Data assignment and update methods for file parameters

For File type parameters, the Data Assignment method that you select, together with your choice of Update method, affect the values that the Vusers use to substitute parameters during the scenario run.

The Data Assignment method is determined by the Select next row field, and the Update method is determined by the Update value on field.

The following table summarizes the values that Vusers use depending on which Data Assignment and Update properties you selected. It also includes an example of each for a table/file that has the following values: Kim; David; Michael; Jane; Ron; Alice; Ken; Julie; Fred.

Update Method | Data Assignment Method
--- | ---
Sequential | Random | Unique
Each iteration | The Vuser takes the next value from the data table for each iteration. Example: All the Vusers use Kim in the first iteration, David in the second iteration, Michael in the third iteration, and continue in this manner until the last iteration, when all the Vusers use Fred. | The Vuser takes a new random value from the data table for each iteration. Example: The Vusers use random values from the table for each iteration. | The Vuser takes a value from the next unique position in the data table for each iteration. Example: For a test run of 3 iterations, the first Vuser takes Kim in the first iteration, David in the second, and Michael in the third. The second Vuser takes Jane, Ron, and Alice. The third Vuser, Ken, Julie, and Fred.
Each occurrence (Data Files only) | The Vuser takes the next value from the data table for each occurrence of the parameter, even if it is within the same iteration. Example: All the Vusers use Kim in the first occurrence, David in the second occurrence, Michael in the third occurrence, and continue in this manner until the last occurrence, when all the Vusers use Fred. | The Vuser takes a new random value from the data table for each occurrence of the parameter, even if it is within the same iteration. Example: The Vusers use random values for each occurrence of the parameter. | The Vuser takes a new unique value from the data table for each occurrence of the parameter, even if it is within the same iteration. Example: The Vuser uses a unique value from the list for each occurrence of the parameter.
Once | The value assigned in the first iteration is used for all subsequent iterations for each Vuser. Example: All Vusers take Kim for all iterations. | The random value assigned in the first iteration is used for all iterations of that Vuser. Example: All Vusers take the first randomly assigned value for all the iterations. | The unique value assigned in the first iteration is used for all subsequent iterations of the Vuser. Example: The first Vuser takes Kim for all iterations, the second Vuser takes David for all iterations, and this pattern continues for each subsequent Vuser.

Note: If you select the Sequential method and there are not enough values in the data table, parameters are returned to the first value in the table, continuing in a loop until the end of the test.

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See also:

- Edit script parameters

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