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. After 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 after 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.
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
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.