About Purging Alarms

Purging alarm data involves deleting the data from the database.

Note:

Even after purging, the data is not lost; a backup is created to maintain an audit trail. You can restore the data if needed.
When using circular archives (that is, archives that roll over), alarms are purged automatically.

You can choose to purge alarm data for any of the following reasons:

To maintain alarm data efficiently
The data is outdated or redundant
The disk space is limited

Data in the following tables is purged:

Alarm Attribute Values
Alarm Attribute Value History
Delete from Alarm History
Delete from Alarm Table esignatures
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You can purge data using one of the following methods:

Purge data within a specified duration. You can do this using Configuration Hub, using the Proficy Historian Alarm and Event Data Migration utility or at a command prompt.
Purge data related to a specific alarm ID. You can do this using Alarms.PurgeAlarmsById to develop an SDK program.

Purging is performed in batches. You can check the log data in the Proficy.Historian.AandE.Migration.log file. By default, this file is located in the C:\Program Files(x86)\Proficy folder.

In the case of a failure:

The batch size is changed to 10. That is, the collector receives an acknowledgement after sending 10 messages, thus reducing the load on the server.
The waiting time for receiving an acknowledgement is automatically incremented after each failure per batch, starting from 90 seconds to 270 seconds. This gives more time for the server to respond.

Note: After the acknowledgement is received, the batch size and the waiting time are reset for the subsequent batches.

If the time taken to purge exceeds the timeout limit, instead of reverting the entire purging operation, only the current batch, which is still under processing, is purged.

Best Practices:

Restart the Alarms and Events services before purging data.