Epoch Management Parameters
The following table describes the epoch management parameters for configuring Vertica.
Parameters | Description |
---|---|
AdvanceAHMInterval |
Determines how frequently (in seconds) Vertica checks the history retention status. Note: Default Value: 180 (3 minutes) Example: ALTER DATABASE mydb SET AdvanceAHMInterval = '3600'; |
AHMBackupManagement |
Blocks the advancement of the Ancient History Mark (AHM). When this parameter is enabled, the AHM epoch cannot be later than the epoch of your latest full backup. If you advance the AHM to purge and delete data, do not enable this parameter. Note: Do not enable this parameter before taking full backups, as it would prevent the AHM from advancing. Default Value: 0 Example: ALTER DATABASE mydb SET AHMBackupManagement = '1'; |
EpochMapInterval |
Determines the granularity of mapping between epochs and time available to historical queries. When a historical queries Tip: Decreasing this interval increases the number of epochs saved on disk. Therefore, consider reducing the HistoryRetentionTime parameter to limit the number of history epochs that Vertica retains. Default Value: 180 (3 minutes) Example: ALTER DATABASE mydb SET EpochMapInterval = '300'; |
HistoryRetentionTime |
Determines how long deleted data is saved (in seconds) as an historical reference. When the specified time since the deletion has passed, you can purge the data. Use the -1 setting if you prefer to use Note: The default setting of 0 effectively prevents the use of the Administration Tools 'Roll Back Database to Last Good Epoch' option because the AHM remains close to the current epoch and a rollback is not permitted to an epoch prior to the AHM. Tip: If you rely on the Roll Back option to remove recently loaded data, consider setting a day-wide window to remove loaded data. For example: ALTER DATABASE mydb SET HistoryRetentionTime = 86400; Default Value: 0 (Data saved when nodes are down.) Example: ALTER DATABASE mydb SET HistoryRetentionTime = '240'; |
HistoryRetentionEpochs |
Specifies the number of historical epochs to save, and therefore, the amount of deleted data. Unless you have a reason to limit the number of epochs, Vertica recommends that you specify the time over which deleted data is saved. If you specify both Default Value: -1 (Disabled) Example: ALTER DATABASE mydb SET HistoryRetentionEpochs = '40'; |