Caching location, configuration and storage considerations

This section describes how caching is managed by the connector and outlines the operational considerations for cache storage, capacity planning, and monitoring in AVEVA PI System Connector 3 (PSC3) deployments.

In general terms, cache management is determined by three interconnected factors:

• The location of the cached data

• The maximum disk space allocated

• The connector’s response when storage capacity is exceeded.

Cache location

The cache location is the folder on your local drive where the connector saves cached data. This folder should be on a disk with ample space and dependable input/output performance, particularly in settings where temporary interruptions are anticipated. The default location is C:\ProgramData\PISystem Connector but can be reassigned at any time.

Note: The cache directory is managed by the connector and should not be modified manually while the connector is running.

Cache file locations

The connector writes cached data to a configurable directory on the local file system. This setting specifies the place where the connector stores buffered data when immediate delivery to its destination is not possible.

In PSC3, the cache files are collected in the following default locations:

Each cache file is stored as a .dat file with a timestamp-based naming convention. Files that failed to send may be renamed with .error extension.

The cache directory is managed entirely by PSC3 and should be treated as persistent operational storage. Selecting a stable, monitored disk location helps ensure reliable buffering during destination outages or periods of increased data volume.

Caution: Do not modify cache files. This may cause irreversible damage to either the data or the connector, potentially compromising their integrity and functionality beyond repair.

Cache size and disk usage limits

The cache size setting defines the maximum amount of disk space the connector may use for cached data. This limit applies only to cache files and does not include other connector logs or artifacts.

A value of -1 MB indicates that no explicit size limit is enforced. This allows the cache to grow based on available disk space. The default is intended to reduce the risk of data loss in environments where disk capacity is managed externally and sufficient storage is available. When storage has reached 90% of the cache size limit, data collection stops.

If long-term caching is required due to prolonged outages, network problems, or large amounts of data, sufficient disk space should be reserved on the connector machine to avoid any interruptions in data collection.

A lack of adequate disk space may lead to failures in data collection, possible data loss if the cache cannot be saved, or service disruptions that need manual fixes. It is crucial to effectively manage the disk space allocated to the PI System Connector cache.

We recommend monitoring the cache directory growth to establish a baseline. Additionally, adjust the cache size limit to provide adequate capacity according to the projected data collection rate (events per second), the volume of historical and real-time data, as well as the maximum anticipated outage period.

You can use the following formula to calculate an estimate cache storage amount:

amount of events/day × amount of KB/event = amount of GB/day

For example, if you had a million events a day and the cache uses 1 kilobyte per event, you should allocate at least 10GB for a seven day outage tolerance.