If your configuration includes an external HDS, you may notice that you are missing records from reports during the Logger recovery process.
If the Logger connected to the external HDS goes offline, the external HDS does not connect to a different Logger. For example, if the external HDS is connected to Logger A and Logger A fails, the HDS does not connect to Logger B. When Logger A comes back up, it recovers data from Logger B and begins to receive current historical information. Once Logger A has recovered all of the data from Logger B, it replicates this data to the external HDS.
If reports are run from the external HDS for recent intervals while Logger A is offline or while the Logger is in the process of recovering or replicating data, you might not see data for those intervals in reports. These records are missing only temporarily; you will see the data once the replication process for the tables used by the reports is complete.
If your deployment does not include an external HDS and Logger A goes offline, you will not see report data from the interval during which Logger A was offline until Logger A has recovered that data from Logger B.
Permanently missing data
The Packaged CCE Logger retention settings and database size are configured to ensure sufficient database space for the data. In the unlikely event that the Logger's Central Database becomes full or reaches a configured threshold size, Packaged CCE frees up database space by running an emergency purge on historical database tables.
The emergency purge goes through each historical table in a predefined order one at a time and purges one hour's worth of data from the table, looping through the tables if necessary. As data is purged from each historical table, a check is made to verify if the free space is more than the minimum threshold value. Once adequate space has been recovered, the emergency purge procedure stops.
If your deployment does not include an external HDS and uses only the Logger for data storage, emergency purge results in a permanent loss of data. If your deployment does include an external HDS, permanent loss of historical data can occur if the emergency purge removes historical data that has not yet made it to an external HDS and been replicated to the peer Logger.