Understanding "Value at this Time Already Exists" in PI System Notifications

In the OSIsoft PI System, encountering errors or notifications is part and parcel of managing and maintaining a complex data infrastructure. One such common notification that users might see is the "Value at this Time Already Exists" message. This can occur frequently and often needs a solid understanding to mitigate or manage.

What Does "Value at this Time Already Exists" Mean?

In the context of the PI System, a message stating "Value at this Time Already Exists" typically indicates that an attempt was made to write a value to a PI tag for a timestamp where a value already exists. This happens most often during data backfills, recalculations, or interface issues.

The message might look something like this:

ErrorpisnapssPostevent failed: [-109] Value at This Time Already ExistsSYSTEM<Number>pisnapmgrPoint ID: <ID>, Connection ID: <ID>, User: piadmin, User ID: <ID>, mode: noreplaceEvent time: <time>, value: <value>

Common Causes

1. Backfilling and Recalculation: Often, when analysis recalculates data, it attempts to rewrite historical values, triggering these errors if the same timestamps are being used.

2. Legacy Notification Tags: If your PI System is using legacy notifications (pre-2016), you might see this error due to the way data is handled in the older infrastructure.

3. Interface Configurations: If an interface is running on your system that doesn’t account for existing data at specific timestamps, it will try to write it regardless, causing errors.

Noise or Genuine Concern?

Typically, these messages can be considered noise, particularly if they relate to legacy notification tags or are expected during recalculations. However, maintaining a clean log is essential for identifying genuine issues. Here are some steps to address this:

Migrating to Modern Notifications

If you haven’t already, consider migrating to PI Notifications 2016+. This modern framework significantly reduces complications arising from legacy components and can help eliminate redundant tag-related messages.

Migrating involves several steps, and a comprehensive guide can be found on OSIsoft’s support portal. How to Migrate from PI Notifications 2012 to PI Notifications 2016+

Review Interfaces

Ensure that any interfaces running on the system are correctly configured to handle existing data policies. Sometimes, tweaking the settings so that they do not rewrite existing data unless absolutely necessary can help lower the occurrence of this error.

Control Backfilling and Recalculations

If backfilling is causing significant amounts of these messages, review your recalculation schedules and data handling approaches to ensure they’re optimized and necessary.

Conclusion

While "Value at this Time Already Exists" errors can be minimized, understanding their origin is vital in ensuring they don't hide more serious issues. With this knowledge, systems administrators can better manage their PI Systems for both operational and analytical success. Proper strategy in handling legacy systems and updating infrastructure can transform these issues from a significant noise factor into a manageable background task.