MAKE_AHM_NOW

Sets the Ancient History Mark (AHM) to the greatest allowable value. This lets you purge all deleted data.

After running this function, you cannot query historical data that precedes the current epoch. Only database administrators should use this function.

MAKE_AHM_NOW performs the following operations:

  • Advances the epoch.
  • Sets the AHM to the last good epoch (LGE) — at least to the epoch that is current when you execute MAKE_AHM_NOW.

Syntax

MAKE_AHM_NOW ( [ true ] )

Parameters

true

Allows AHM to advance when one of the following conditions is true:

  • One or more nodes are down.
  • One projection is being refreshed from another (retentive refresh).

In both cases , you must supply this argument to MAKE_AHM_NOW, otherwise Vertica returns an error. If you execute MAKE_AHM_NOW(true) during retentive refresh, Vertica rolls back the refresh operation and advances the AHM.

If the function advances 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 MAKE_AHM_NOW with an argument of true; otherwise, the function returns an error.

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

In the following example, MAKE_AHM_NOW advances the AHM even though a node is down:

=> SELECT MAKE_AHM_NOW(true);
WARNING:  Received no response from v_vmartdb_node0002 in get cluster LGE
WARNING:  Received no response from v_vmartdb_node0002 in get cluster LGE
WARNING:  Received no response from v_vmartdb_node0002 in set AHM
         MAKE_AHM_NOW
------------------------------
 AHM set (New AHM Epoch: 684)
(1 row)

See Also