Understand backfilling and recalculation of analyses

When you backfill an analysis for a specified time range, data that are missing are calculated to fill in the gaps for the outputs. Recalculation, on the other hand, deletes all of the data in the time range and calculate results for the analysis outputs again. Currently, there are four different options of backfill and recalculation. For more information, see the knowledge base article Asset analytics backfilling and recalculation milestones and requirements.

Expression, rollup or SQC analyses can be backfilled or recalculated over an earlier time period if the analyses outputs are mapped to PI point attributes. You can backfill the missing data in a time range and retain existing data, or you can recalculate, which deletes and recalculates data in the time range. Event frame generation analyses can recalculate event frames over a specified time period, but automatically delete all existing event frames in that time period, as well as annotations on affected event frames.

In order to backfill/recalculate, you need Execute permission on the analyses. Proper permission can be obtained by mapping your account to Asset Analytics Recalculation identity. For more information on identity mapping, see PI AF identities and mappings.

Note: For analyses writing outputs to attributes configured as PI point, backfilling or recalculation may result in writing out-of-order events. Such events are written to the Data Archive without compression.

Enabling automatic backfilling is useful as it fills the gaps in case a short analysis service downtime occurs. For more information, see parameters AutoBackfillingEnabled and MaximumAllowedAutoBackfillingSpanInHours in Understand PI Analysis Service settings.

From PI AF 2017 R2, you can enable automatic recalculation of analyses. PI AF Server and PI Analysis Service 2017 R2 or later are required to make use of automatic recalculation. Although automatic recalculation is globally enabled by default (AutoRecalculationEnabled), you need to opt in at individual analysis (template) level if you expect late-arriving or out-of-order data that may trigger recalculation. For more information, see Configure automatic recalculation of analyses and analyses templates, Enable or disable automatic recalculation for multiple analyses and parameters AutoRecalculationEnabled, AutoRecalculationIgnoreTimeInSeconds, AutoRecalculationMinWaitTimeInSeconds, and MaxAllowedAutoRecalculationSpanInDays in Understand PI Analysis Service settings. To examine a log file with a list of queued automatic and manual backfill/recalculation requests for troubleshooting, see Open the recalculation log folder.

Note: Event frame generation and SQC analyses that are configured to generate event frames are excluded from automatic recalculation.