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Monitoring the Ancient History Mark

Also known as AHM, the ancient history mark is the oldest epoch whose data is accessible to historical queries. Any data that precedes the AHM is eligible to be purged. If a cluster nodes is down or if a database contains projections that need to be refreshed, the AHM can lag behind the Current Epoch (CE) increasing the catalog size and degrading query performance.

You can view the AHM and CE in several ways.

Example:

dbadmin=> SELECT ahm_epoch, current_epoch FROM v_monitor.system;
 ahm_epoch | current_epoch
-----------+---------------
      6680 |          6681

dbadmin=> SELECT get_ahm_epoch(), get_current_epoch();
 get_ahm_epoch | get_current_epoch
---------------+-------------------
          6680 |              6681
(1 row)

It’s also really helpful to now when the AHM last advanced!

dbadmin=> SELECT get_ahm_time();
                  get_ahm_time
-------------------------------------------------
 Current AHM Time: 2018-05-21 09:48:39.075679-04
(1 row)

Have Fun!

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