Previewing a flow

You can preview a flow to help build or fine-tune the flow. When you preview a flow, you can see how source data passes through the flow and review how each stage changes the data.

Preview provides data under the following conditions:
  • All stages in the canvas are connected.

    You can preview both complete and incomplete flows when the source and all stages in the canvas are connected.

  • All required properties are defined.

    You can enter any valid value for required properties, even if they are not the final values that you intend to use.

You can configure preview settings such as the preview batch size and preview timeout, and whether preview writes to targets and executors. You can also specify whether preview runs for all stages in the flow or a subset of stages.

To preview data, click the Preview icon: eye icon, and then click Preview.

After you run preview, you can review preview data for one stage at a time. You can view the data in a list view or a table view. When you use list view, preview displays the output records for each stage in the same row as the corresponding input record, when possible. With this order, you can easily compare the input and output data to view the changes made by the stage.

You can also edit the flow or update stage properties, and then run the preview again to see how your changes affect the data flow.

Views

Preview provides the following ways to review preview data for a flow:
List view
List view displays preview data in lists. List view provides both the input and output data for stages, when available. When List view shows both sets of data, you can see how individual stages affect the data.
For example, when a processor is connected to both upstream and downstream stages, list view displays the input data and the output data for the stage. You can update the processor or other flow configuration, and then rerun the preview to see the results of your changes.
List view also displays the data type for each field.
To display preview data in list view, click the List View icon: list icon.
Table view

Table view displays preview data in a table. Table view provides output data for source and processor stages, and input data for target and executor stages.

To display preview data in table view, click the Table View icon: table icon.

Preview data types

In list view, preview displays the Data Collector data types for each field.

Preview uses the default format of the browser locale to display date, datetime, and time data. For example, if the browser uses the en_US locale, preview displays dates using the following format: MMM d, y h:mm:ss a.

Preview also displays datetime data in relationship to the browser time zone.

Writing to targets and executors

Since previewing a flow is a tool for development, preview does not pass data to target or executor stages, by default. You can, however, view the data that is passed to a target stage, which is typically similar to what is written to target systems.

When needed, you can configure preview to write data to target and executor stages. When writing to targets and executors, preview writes data to target systems and passes data to executors, which triggers their actions. For example, you might enable passing data to an executor to verify that it performs the configured task as expected.

To write to targets and executors, modify preview properties and enable the Write to targets and executors property.

Important: Avoid writing preview data to or triggering executor actions in production systems.

Modifying preview properties

About this task

Preview uses default preview settings to preview a flow by default. You can configure preview properties before you preview a flow.

Your changes are used for the duration of your flow configuration session by default. To save your preview settings for later reuse, save the flow after you exit preview.

For example, if you preview a flow and then leave the flow canvas without saving the flow, the next time that you preview the flow, preview uses the default settings.

Procedure

  1. While viewing the flow, click the Preview icon: eye icon. Then, click Configure preview.
  2. In the Preview Configuration dialog box, configure the following properties.
    Preview property Description
    Preview batch size Number of records to use in the preview.

    Default is 10.

    Preview timeout Milliseconds to wait for preview data. Defines the time that preview waits for the source stage to receive data.

    Used for flows that include a transient source, such as the HTTP Client source.
    Run preview through stage Previews the flow from the source stage to the selected stage.

    Use to preview a partial flow when a stage in the flow generates an error.

    For example, if preview fails because a processor encounters an error, you can run the preview up to the stage upstream from the processor. Then you can view the preview data and update the processor configuration as needed.
    Time zone Time zone used to display date, datetime, or time data.

    Default is the browser time zone.
    Write to targets and executors Determines whether the preview writes data to target systems and passes data to executors in the flow, triggering their actions in external systems.

    By default, preview does not write data to target systems or pass data to trigger executors.
    Execute flow lifecycle events Runs lifecycle events for the flow.
    Show record/field header Displays record header attributes and field attributes in list view. Attributes do not display in table view.
    Show field type Displays the data type for fields.
  3. To run preview, click Run preview.
    Preview uses the specified settings as you configure the flow. The settings are not saved for reuse until you save the flow.
  4. To save preview settings changes with the flow, click Exit preview, and then click Save to save the flow.

Additional preview details

Consider the following details when you preview flows:
  • Oracle CDC flows - When you preview a flow that includes the Oracle CDC source, preview generates a maximum of 10 records. Preview ignores the Preview batch size property when the property is set to a higher value.

    Also, preview allows up to 5 seconds for the source to receive records after connecting to Oracle. As a result, when previewing a flow with an Oracle CDC source, preview ignores the configured Preview timeout property when it is set to a higher value.

  • Oracle CDC Client flows - Due to the complex nature of the Oracle CDC Client source, initiating preview can take longer than expected. If preview times out, try increasing the Preview timeout property incrementally to allow the source time to connect.

    Also, to generate more than one preview record, set the Max batch wait time property for the source to a value greater than 0.

  • Whole file data format - When you preview a flow that processes whole file data, preview displays only one record.