User Guide

The Replication Client sends a request to the Replication Server requesting historical data that
have associated Recovery Keys higher than those currently on corresponding historical table.
The Replication server sends the requested data back as a set of 2000 records each time.
The Replication server reads the historical data from the actual tables on the Logger and sends
it to the Replication Client which writes the historical data to the actual corresponding tables
in the HDS database. Temporary tables are not used to replicate the data from the Logger to the
HDS.
Possible Points of Delay or Inconsistency
If the Logger connected to the HDS goes offline, the HDS does not connect to a different Logger.
For example, if the HDS is connected to Logger B and Logger B fails, the HDS does not connect
to Logger A. When Logger B comes back up, it recovers data from Logger A and begins to
receive current historical information. Once the Logger has recovered all of the data from Logger
A, it begins to replicate this data to the HDS.
If reports are run from this HDS for recent intervals while the Logger 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. This is temporary, and you will see the data once the replication process
for the tables used by the reports is complete. If you are using a fault-tolerant system with two
HDS Distributor Admin Workstations, you can run reports using the backup HDS while the
primary HDS is not receiving data.
If the HDS goes offline and you are using a fault-tolerant system with two HDS Distributor
Admin Workstations, you can run reports using the backup HDS. When the HDS comes back
up, it recovers data from the last HDS data backup and also replicates data from the Logger for
the most recent data not available in the backup.
The recovery data replication is faster than regular Logger-HDS data replication. Once the HDS
has recovered to its typical Logger-HDS latency of one to five minutes, data replication proceeds
as usual.
If you are not using a fault-tolerant system, you will not see data in historical reports until the
HDS is restored. You might also notice missing data as the replication process is in progress.
This is temporary and you will see the data once the replication process for the tables utilized
by the reports is complete.
Preventing Data Loss from Logger and HDS Failure
Data loss manifests as 'data holes', which are one or more missing records in an historical
database table.
There are two types of data loss: temporary and permanent:
•
A temporary data hole can happen during the Logger recovery process. For example, LoggerA
goes down, then comes back up and contacts LoggerB to synchronize and recover historical
data that was written while it was down.
Reporting Guide for Cisco Unified ICM Enterprise & Hosted Release 7.2(1)
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Chapter 10: Reporting Implications of Data Loss and Component Failover
Preventing Data Loss from Logger and HDS Failure