Limitations

The following section describes the known limitations imposed on an application running in the point caching configuration.

Extended Attribute Lengths

To maximize the functionality of the point caching configuration, the use of a PI Server version 3.4.370 or later is required. The use of PI Server version 3.4.370 or later in conjunction with PI API version 1.6.8.x or later provides greater field lengths for the tag, descriptor, ExDesc, instrumenttag, and pointsource attributes. The following table lists the maximum field lengths for a given PI Point attribute for the version of PI Server used. In all cases, the PI API version is assumed to be 1.6.8.x or later to support point caching.

Attribute Maximum Length (PI API 1.6.8.x or later on Application Node)

Attribute PI Server 3.4.370.x or higher PI Server Below 3.4.370.x
Tag 1023 255
Descriptor 1023 26
ExDesc 1023 80
InstrumentTag 1023 32
PointSource 1023 1

Note: If the actual data stored for the point attribute is greater than the maximum field length specified in the table, the returned value for the attribute is be truncated to the maximum length for the given PI Server version.

UNIX and Linux

UNIX and Linux use case sensitive file paths. Therefore, the file path to the location of the cache files as defined in the SCacheConfig structure passed to the picm_opencache function must exist and is case sensitive. Failure to define the exact case sensitive cache file directory will result in the failure to create the caching files necessary for point caching and cause the application to shutdown.

The following is an example of a valid lowercase named file path.

/opt/home/piadmin/pi/clients/applications/random/
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