MAKE_AHM_NOW

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

Caution: 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:

Syntax

MAKE_AHM_NOW ( [ true ] )

Parameters

true

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

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

In either case, 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.

Privileges

Superuser

Setting AHM When Nodes Are Down

If you run MAKE_AHM_NOW while any node is down, you must supply an argument of true; otherwise, Vertica returns an error. 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)

Caution: If the AHM is advanced beyond the last good epoch of the failed nodes, those nodes must recover all data from scratch.

See Also