Retrieval of large amounts of data

For each data item in a function, PI DataLink must make a call to either Data Archive or PI Asset Framework to retrieve values. When PI DataLink retrieves values for large numbers of data items, processing each call separately can result in a long retrieval time. To reduce this time, PI DataLink makes bulk calls for certain functions under certain conditions.

The following conditions must be satisfied to make a bulk call:

• Function inputs specify data items, and not expressions or filter expressions

• Function input specifies data items with a reference to a cell range

• PI DataLink settings specify time stamps in client time zone

With the above conditions satisfied, the following functions make bulk calls:

• Current Value

• Archive Value

• Calculated Data (without time interval specified)

PI DataLink returns values from a bulk call in a single function array.

Bulk calls result in performance improvements when functions retrieve values for more than 1,000 data items or in environments with latency between PI DataLink and data sources. When functions retrieve values for more than 10,000 data items, bulk calls reduce retrieval time by an order of magnitude. Therefore, when creating worksheets that retrieve values for large numbers of data items, consider using these functions under the required conditions.