Rockwell Automation FactoryTalk Historian SE 3.0 UniInt Interface User Guide - Manual (Page 69)

UniInt Interface User Manual 63
The point cache file is constructed in a similar fashion to the digital cache file. During
interface startup, the interface requests and receives all points matching the required point
source parameter listed in the startup command file. Upon receipt of the requested points
from the Historian Server, the point record along with the associated extended attributes are
requested from the Historian Server and immediately stored in the point cache file. The
interface may request additional points such as event counters or trigger points. These points
are cached as well. As a rule, any point requested by the interface will result in the point
record and associated extended attributes being cached.
The initial construction of the cache files will require additional startup time for the
interface. When constructing the digital cache file, network latency may add to the startup
time if the entire system digital set table is cached because an additional 1,024 network calls
(one for each possible system digital state) will need to be executed because the interface is
only capable of retrieving a single digital state from the Historian API for a given call.
Historian Points with large digital sets will also require additional caching time. The caching
of the point record and extended attributes will add additional startup time to the interface as
well.
However, restarting the interface in a disconnected startup configuration with a fully
constructed point cache file will eliminate all network calls and latency associated with
communicating with the Historian Server. This will dramatically reduce the interface startup
time for subsequent interface restarts and allow the interface to collect data from the Data
Source much quicker than without running in a disconnected startup configuration.
The ―Messages‖ section of this document contains a listing of typical messages sent to the
pipc.log file during the construction mode.
Utilization
Note: If one or both of the cache files becomes invalid at any time during run-time, the
interface will disable the caching feature of the disconnected startup configuration
and continue to operate in the normal non-caching operating profile. During
normal operation, a connection to the Historian Server is required to retrieve point
update information.
The utilization mode is the run-time use of the caching files that have been validated and
fully constructed. In this mode, all requests for digital state or point attribute data will be
routed to and managed by the API Cache Manager. Requested data will be retrieved from
the appropriate cache file and returned to the interface. While the cache files are in a fully
configured and valid state, no network calls will be made to the Historian Server to retrieve
the requested information.
The utilization process using fully configured cache files allow the following run-time
operations without requiring a connection to the Historian Server.

Validate cache files to be used for interface instance.

Retrieve Historian Server version information.