Troubleshooting PI ACE Calculations Stuck in "Starting" State

PI ACE (Advanced Computing Engine) is a powerful calculation engine frequently used in PI System environments for automated data processing. Occasionally, users encounter a frustrating situation: newly deployed calculations remain in the "Starting" state and don't execute as expected. This blog post explores common causes of this issue and provides a structured troubleshooting approach for PI System administrators and developers.

Scenario Overview

A typical case involves a developer who successfully creates and deploys a PI ACE calculation using Visual Studio, then registers it in PI ACE Manager. However, upon checking PI ACE Manager, the calculation status stubbornly stays on "Starting" instead of transitioning to the green "Running" state. A deeper dive into Task Manager reveals the expected PI ACE components (e.g., PIACEManager, piacenetscheduler.exe) but the crucial PIACEClassLibraryHost.exe process—the one responsible for executing the calculation DLL—is conspicuously missing.

Let's look at logical troubleshooting steps and best practices for resolving this type of situation.

1. Verify PI Trusts for All ACE Components

A common culprit is incomplete or misconfigured PI Trusts. Every PI ACE component that connects to the PI Server—including the ACE Scheduler (piacenetscheduler.exe), the calculation host (PIACEClassLibraryHost.exe), and the ACE executable itself—must have appropriate trust configured on the PI Server.

Action Steps:

• In PI System Management Tools (SMT), ensure you have trusts configured for:
  • piacenetscheduler.exe
  • PIACEClassLibraryHost.exe
  • the PI ACE calculation user (if running under a dedicated account)
• Double-check the trust parameters: IP address/range, application name, and user mapping.
• See: OSIsoft KB00516 - PI ACE calculations remain in the "Starting" or "Stopping" state

2. Check If the Host Process (PIACEClassLibraryHost.exe) Spawns

The PI ACE Scheduler should automatically launch PIACEClassLibraryHost.exe whenever it needs to execute a calculation. If this process isn't appearing in Task Manager:

Action Steps:

• Restart the PI ACE Scheduler service (piacenetscheduler.exe). Use Windows Services manager or the command prompt.
• Watch Task Manager and Event Viewer for errors when attempting to start new calculations.
• Verify that your deployed calculation DLLs are placed in the correct directory (PIACEin) and registered properly.

3. Check for PI ACE Version Compatibility and .NET Issues

Incorrect .NET versions or mismatched PI ACE installation files can block proper calculation hosting.

Action Steps:

• Ensure your development environment (e.g., Visual Studio 2013) generates DLLs compatible with your deployed PI ACE version.
• Verify .NET version compatibility listed in the PI ACE release notes and documentation.
• If possible, rebuild your calculation project targeting the correct .NET framework (commonly .NET 3.5 or 4.0 for legacy ACE).

4. Consult OSIsoft Documentation and Support

If all else fails, OSIsoft's resources are invaluable:

• Troubleshooting PI ACE. v2.1.8 - YouTube.
• Knowledge base articles and the PI Square Community.
• OSIsoft Tech Support can schedule a remote session for advanced diagnostics.

Summary

Resolving stuck PI ACE calculations is a process of elimination: double-check PI Trusts, confirm the host process is spawning, validate compatibility, and don't hesitate to engage support for persistent issues. With structured troubleshooting, you can get your PI ACE calculations back to green and running smoothly!

Do you have more PI ACE troubleshooting tips or war stories? Share them in the comments below!