Manage backfill for the objects of a stream

Overview

A stream in Datastream can backfill historical data, as well as stream ongoing changes into a destination. As part of creating a stream, you configured information about the source database for the stream.

If you selected the Backfill historical data checkbox, then Datastream will stream all existing data, in addition to changes to the data, from the source into the destination.

If you didn't select this checkbox, then Datastream will stream only changes to the data. To have Datastream stream a snapshot of all existing data from the source to the destination, you must initiate backfill for the objects that contain this data. The objects are in the form of database schemas, tables, and columns.

Another reason for initiating backfill for an object is if data is out of sync between the source and the destination. For example, a user can delete data in the destination inadvertently, and the data is now lost. In this case, initiating backfill for the object serves as a "reset mechanism" because all data is streamed into the destination in one shot. As a result, the data is synced between the source and the destination.

After initiating backfill for an object, you can stop backfill for it. In the example above, the user modifies the database schema, and the schema or data is corrupted. You don't want this schema or data to be streamed into the destination, and so you stop backfill for the object.

You can also stop backfill for objects for load balancing purposes. Datastream can run multiple backfills in parallel. This may put an additional load on the source. If the load is significant, stop backfill for the objects, and then initiate backfill for them, one by one.

Object statuses

The various statuses in the lifecycle of initiating and stopping backfill for an object include:

  • No status (represented in the UI as -): Reasons for an object receiving this status include:
    • The stream hasn't been started.
    • The Backfill historical data checkbox wasn't selected (so the backfill is defined as manual).
    • The object is excluded explicitly from being backfilled automatically.

    • The stream is configured to include future tables. If this happens, then when new tables are added to the source, there's no automatic backfill task created for them (because new tables typically don't have any "historical" data to backfill).

      For more information, see Configure information about the source database for the stream.

  • Pending: Backfill hasn't yet started for the object.
  • Active: Backfill is in progress for the object.
  • Completed: Backfill is completed for the object.
  • Stopped: Backfill is stopped for the object. If backfill is initiated again for the object, then Datastream will stream all existing data associated with the object from the source into the destination.
  • Failed: Backfill failed for the object and the backfill must be initiated again.

Initiate backfill

  1. Go to the Streams page in the Google Cloud Console.

    Go to the Streams page

  2. Click the stream that contains objects for which you want to initiate backfill.

  3. Click the OBJECTS tab.

  4. Select the checkbox for each object for which you want to initiate backfill.

  5. Click INITIATE BACKFILL.

  6. If you selected only one object, then in the dialog, click INITIATE OBJECT BACKFILL. Otherwise, if you selected multiple objects, then click INITIATE OBJECT BACKFILLS.

    Datastream will start backfill for the objects that you selected, and the status of each object will change from Pending to Active to Completed. When an object has a status of Completed, this means that Datastream has read all the data for the object, but the data might still be loading to the destination.

Stop backfill

  1. Go to the Streams page in the Google Cloud Console.

    Go to the Streams page

  2. Click the stream that contains objects for which you want to stop backfill.

  3. Click the OBJECTS tab.

  4. Select the check box for each object for which you want to stop backfill.

  5. Click STOP BACKFILL.

  6. If you selected only one object, then in the dialog box, click STOP OBJECT BACKFILL. Otherwise, if you selected multiple objects, then click STOP OBJECT BACKFILLS.

    Datastream will stop backfill for the objects that you selected, and the status of each object will change to Stopped.

    When an object has this status, backfill is stopped for the object. If backfill is initiated again for the object, then Datastream will stream all existing data associated with the object from the source into the destination.

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