MAKE_AHM_NOW

Sets the (AHM) to the greatest allowable value.

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

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.

This is a meta-function. You must call meta-functions in a top-level SELECT statement.

Behavior type

Volatile

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.

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.

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