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.
- Performs a moveout operation on all projections.
- Sets the AHM to the last good epoch (LGE) — at least to the epoch that is current when you execute
MAKE_AHM_NOW ( [ true ] )
Allows AHM to advance when one of the following conditions is true:
In both cases , you must supply this argument to
If the function advances AHM beyond the last good epoch of the down nodes, those nodes must recover all data from scratch.
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)