User Guide

Table Of Contents
Two Distributor Admin Workstations are typically set up as HDS machines. A similar
fault-tolerant strategy applies to the HDSwhen the primary HDS fails, the client Admin
Workstation automatically switches over to use the backup HDS.
Each Historical Data Server (HDS) is connected to a single Logger.
Sections in both Chapter 1 (page 8) and Chapter 2 (page 21) discuss the relationship between
the Logger and historical data.
Understanding Recovery and Replication
Recovery Keys
The recovery key is the base key for all historical data tables. This key is always incremented
by 1 before a new record is inserted into any historical table.
In a duplex conguration, the Logger that nishes initializing rst is designated the primary
Logger (although both the Loggers are always active and working in parallel). The recovery
key is always initialized by the primary Logger. The recovery key is based on the current GMT
date and time and always has a value greater than any previous value generated. This helps the
recovery process to keep the Loggers in sync.
The replication process may have a latency of about one to ve minutes because the Logger
replicates data table-by-table on the HDS.
Temporary Tables
Each historical table on the Logger Central Database has two corresponding temporary tables
that act as buffers to incoming historical data. As they have minimal indexes, the temporary
tables speed up the process of inserting data into the corresponding actual table in the Logger
Central Database.
Recovery Process
As the incoming historical data is written to the corresponding temporary tables by the Logger,
the Recovery process reads the data from the temporary tables and performs a bulk insert
operation of up to 2000 records into the actual historical tables.
In a duplex conguration, the recovery process keeps the historical data on the two Loggers in
sync, using the Recovery Keys. The historical data between the Loggers is synced directly using
actual tables; temporary tables are not used by the recovery process.
Replication
The Replication process is responsible for replicating data that has been committed to the Logger
Central database to the HDS database.
The Replication mechanism consists of two processes: the Replication Server Process that runs
on the Logger and the Replication Client Process that runs on the Distributor on which HDS
has also been installed.
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
Data Flow from Logger to Historical Data Server