Manually Purging Data

You manually purge deleted data as follows:

  1. Determine the point in time to which you want to purge deleted data.
  2. Set the ancient history mark (AHM) to this point in time using one of the following functions:

    When you use SET_AHM_TIME or GET_AHM_TIME, keep in mind that the timestamp you specify is mapped to an epoch, which by default has a three-minute granularity. Thus, if you specify an AHM time of 2008-01-01 00:00:00.00, the resulting purge might permanently remove as much as the first three minutes of 2008, or fail to remove the last three minutes of 2007.

    The system prevents you from setting the AHM beyond the point where it prevents recovery in the event of node failure.

  3. Purge deleted data from the desired projections with one of the following functions:

    The tuple mover performs a mergeout operation to purge the data. Vertica periodically invokes the tuple mover to perform mergeout operations, as configured by tuple mover parameters. You can manually invoke the tuple mover by calling the function DO_TM_TASK.

Manual purge operations can take a long time.