Epoch management parameters

The following table describes the epoch management parameters for configuring Vertica.

AdvanceAHMInterval

Determines how frequently (in seconds) Vertica checks the history retention status.

AdvanceAHMInterval cannot be set to a value that is less than the EpochMapInterval.

Default: 180 (seconds)

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.

Caution

Do not enable this parameter before taking full backups, as it would prevent the AHM from advancing.

Default: 0

EpochMapInterval

Determines the granularity of mapping between epochs and time available to historical queries. When a historical queries AT TIME T request is issued, Vertica maps it to an epoch within a granularity of EpochMapInterval seconds. It similarly affects the time reported for Last Good Epoch during Failure recovery. Note that it does not affect internal precision of epochs themselves.

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: 180 (seconds)

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Determines how long deleted data is saved (in seconds) as an historical reference.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 HistoryRetentionEpochs to determine which deleted data can be purged.

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 DEFAULT SET HistoryRetentionTime = 86400;

Default: 0 (Data saved when nodes are down.)

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 History parameters, HistoryRetentionTime takes precedence. Setting both parameters to -1, preserves all historical data.

See Setting a purge policy.

Default: -1 (disabled)