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PI System Connector

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Operational overview

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  • Last UpdatedAug 28, 2023
  • 6 minute read

This section provides an overview of how PI System Connector replicates AF objects from the source PI System to the destination PI System.

AF Replication

The connector supports the following options to replicate AF objects: Replicate AF and Data Archive and Replicate AF only. Unless otherwise stated, the procedures below apply to both configurations.

Initial Check at Startup

Prior to copying AF data to the destination AF server, PI System Connector checks to ensure that all standard (Table Lookup, Formula, PI point, PI point Array, and String Builder) and custom AF data references present on the source AF database also exist on the destination AF database. This is to prevent errors during lengthy import operations on the destination that would effectively cause the import to fail.

Caution: This is a critical step and will prevent the PI System Connector from proceeding further if one or more data references do not exist on the destination. Any missing standard and custom data references must be installed on the destination AF server prior to starting the connector.

Upon successful completion of the AF data reference check, the following will occur:

  • Start full export of the source AF database.

    • Export the source AF server UOM objects (UOM classes and UOMs) and send the UOM objects to the destination AF Server.

    • Export the source AF database.

    • Process the exported AF database to find all the referenced PI points.

    • Prepare the exported AF database for import on the destination. This includes altering PI point configuration strings to include any prefixing done by the connector and relay.

    • Send the exported AF database to the destination.

    • Prepare found PI point information for data collection (Replicate AF and Data Archive option).

    • Start the AF discovery task.

  • Or, start full export of a source AF element.

    • Export the UOM objects (UOM classes and UOMs) and send the UOM objects to the destination AF Server.

    • Export the source AF element.

    • Export the referenced AF objects of the AF element and its children.

    • Send the exported referenced AF objects to the destination AF Server.

    • Process the exported source AF element to find all the referenced PI points.

    • Prepare the exported source AF element for import on the destination. This includes altering PI point configuration strings to include any prefixing done by the connector and relay.

    • Send the exported source AF element to the destination relay.

    • Prepare found PI point information for data collection (Replicate AF and Data Archive option).

    • Start the AF discovery task.

Connector Restart

The following steps occur on a restart:

  • If no previous export exists for the connector, the connector performs a full export as described above. Otherwise, the connector exports only the changes that occurred since the last discovery event.

  • Start the AF discovery task.

Discovery

AF discovery is a task that periodically checks for changes that have occurred in the source AF database since the initial startup or the last discovery event. The discovery task uses a timestamp that is updated immediately on the request for changes. During this discovery operation, pertinent changes are sent to the destination AF database. This includes AF object additions, AF object deletions and AF object updates. The timestamp is persisted and is read on the restart of the connector.

PI Point Replication: Replicate AF and Data Archive and Replicate Data Archive only

This section applies to the replication of PI points from the source PI System to the destination PI System. The connector supports the following options to replicate PI point data: Replicate AF and Data Archive and Replicate Data Archive only. Unless otherwise stated, the procedures below apply to both configurations.

Initial Startup

PI System Connector collects data for PI points associated with data source configurations. For Replicate AF and Data Archive configurations, the connector identifies PI points for data replication through AF Data References. For replication of data archive only configurations, the connector does not require connectivity to an AF server or database. The connector identifies PI points for data replication by querying the source Data Archive for PI points that match the query defined in the configuration.

It does not matter which replication option you select, a PI Point is only replicated once, regardless of how many times it is referenced in the AF or PI Data Archive.

Note: The Global Query only applies to Replicate Data Archive only option, and not to any other replication setting type.

The data collection involves the following steps:

  • Load PI points from their respective source Data Archive.

  • Send selected PI point attributes for PI point replication on destination Data Archive.

  • Backfill history data for the PI points.

  • Collect current archive data for the PI points after backfill completes.

  • Collect snapshot data for the PI points that have compression disabled/off as indicated by the PI point attribute compressing=0 after backfill completes.

  • If a global snapshot query is defined for a specific source Data Archive, replicate snapshot data for the PI points that match the source Data Archive snapshot query regardless of compressing attribute.

  • Start the PI point discovery task.

PI System Connector supports history recovery. On initial start, it starts to backfill up to the configured History Recovery Start Time for all the PI points. PI System Connector collects current archive data by signing up on the PI points as a consumer of the source Data Archive. PI points that complete the backfill will be added to the consumer sign-up list and start collecting current archive data. Likewise, PI System Connector collects current snapshot data by signing up on the PI points as a consumer of the source PI Snapshot Subsystems. PI points that have compression disabled/off, or satisfy the snapshot query, and complete backfill will be added to the consumer sign-up list and start collecting current snapshot data.

Connector Restart

On restart, PI System Connector checks for the last update time of all the PI points and recovers history data from either the last update time of each PI point or up to the configured History Recovery Start Time, whichever is more recent.

Note: Some program data files may contain sensitive data. To restrict access to these files, members of the Users group should be limited to accounts with full access to the source AF database.

Discovery

The PI point discovery task auto-discovers the new points added to the configured source database or source AF element branch through PI Point Data References. When a source Data Archive is specified in connector data source configuration, it also discovers the changes in the PIPOINT database of the source Data Archive. Any new PI points discovered will be created and an initial backfill up to the History Recovery Start Time defined in the Global Settings for the data source will be performed before streaming the current data.

Operational comments

The following comments relate to general PI System Connector operation.

  1. PI System Connector never creates or alters PI points on source Data Archives.

  2. PI System Connector never creates or alters the AF structure on the source AF.

  3. PI points referenced by the AF structure referenced in the Replicate AF and Data Archive or matching the query associated with the Replicate Data Archive only data source configuration options are created and updated on the destination Data Archive.

  4. PI System Connector will not create a PI point referenced by the AF structure if the export conducted by PI System Connector to the destination is completed before the PI point was created on the source Data Archive. The AF structure must be updated or resynchronized using the Resync option found on the data source configuration page so that the connector will reread the AF structure, which will pick up the change.

  5. PI System Connector does not interpret the %Element%.%Attribute substitution parameters found in the AF export. The connector only checks for configuration strings that map to existing points.

  6. PI points referenced by the AF structure referenced in the Replicate AF and Data Archive will be replicated indefinitely, even if they are removed from the original source AF database or if the original data source configuration that included them is removed. For exclusion and removal control, use a combination of Replicate Data Archive only and Replicate AF only.

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