SET_AHM_EPOCH

Sets the Ancient History Mark (AHM) to the specified epoch. This function allows deleted data up to and including the AHM epoch to be purged from physical storage.

SET_AHM_EPOCH is normally used for testing purposes. Instead, consider using SET_AHM_TIME which is easier to use.

Syntax

SET_AHM_EPOCH ( epoch, [ true ] )

Parameters

epoch

Specifies one of the following:

  • The number of the epoch in which to set the AHM
  • Zero (0) (the default) disables PURGE

The number of the specified epoch must be:

  • Greater than the current AHM epoch
  • Less than the current epoch

Query the SYSTEM table to view current epoch values relative to the AHM.
true

Allows the AHM to advance when nodes are down.

If you advance AHM beyond the last good epoch of the down nodes, those nodes must recover all data from scratch.

Privileges

Superuser

Setting AHM When Nodes Are Down

If any node in the cluster is down, you must call SET_AHM_EPOCH with an argument of true; otherwise, the function returns an error.

This requirement applies only to Enterprise mode; in Eon mode, it is ignored.

Examples

The following command sets the AHM to a specified epoch of 12:

=> SELECT SET_AHM_EPOCH(12);

The following command sets the AHM to a specified epoch of 2 and allows the AHM to advance despite a failed node:

=> SELECT SET_AHM_EPOCH(2, true);

See Also