i4SCADA - IIS Performance Tuning with Application Pool recycling

IIS Application Pool Settings are important for the performance and stability of your web applications.

Why is this so important ?

1. Memory Management:
   • Prevent Memory Leaks: Over time, applications may develop memory leaks, consuming more memory than necessary. Recycling helps reclaim resources and prevent these leaks
   • Fragmentation: Even without leaks, memory fragmentation can occur, leading to inefficient memory usage. Recycling helps mitigate this issue
2. Performance Optimization:
   • Resource Reclamation: Recycling ensures that unused resources are freed up, maintaining optimal performance.
   • Fresh Start: It provides a fresh start for the application, which can improve responsiveness and reduce latency.
3. Stability and Reliability:
   • Prevent Crashes: Regular recycling can prevent application crashes caused by resource exhaustion or other issues.
   • Consistent Performance: It helps maintain consistent performance by periodically resetting the application state.
4. Scheduled Maintenance:
   • Off-Peak Hours: Recycling can be scheduled during off-peak hours to minimize disruption to users.
   • Application Updates: After deploying updates, recycling ensures that the new code is loaded and running.
5. Configuration Flexibility:
   • Customizable Settings: IIS allows you to configure recycling based on various parameters such as time intervals, specific times, request limits, and memory usage.

Overall, recycling is a proactive measure to ensure that web applications remain stable, performant, and reliable over time.

A very helpful guide to best practice can be found here: 10 IIS application pool settings best practices

Note: There is no "one size fits all" solution. The settings can vary depending on the physical environment and resources as well on the running application.

Suggested settings for i4SCADA:

• Idle-Timeout
  • reduce the default from 20 to 10
• Regular interval
  • reduce from default 1740 to 720
• Rapid Fail protection
  • Set to True
  • Keep default interval 5 errors in 5 minutes
• Maximum Worker Processes / WEB Garden
  • Use a thumb rule of 1 WP per CPU core
  • Use this setting with care
  • More worker processes will use more ressources
• CPU-Limit
  • Use 80 - 90% as a thumb rule
• Private memory limit / virtual memory limit
  • Private Memory Limit:
    • Definition: Private Memory refers to the physical memory (RAM) allocated exclusively to a worker process. This memory is not shared with other processes
      Function: When the private memory limit is reached, the application pool is recycled to prevent excessive memory usage and potential memory leaks
    • Usage: This limit helps ensure that a single process does not consume too much physical memory, which could affect the overall performance of the server
  •  Virtual Memory Limit:
    • Definition: Virtual Memory includes both the physical memory and the paging file on the disk. It represents the total memory that a process can reserve
    • Function: When the virtual memory limit is reached, the application pool is recycled to prevent the process from reserving more memory than is available
    • Usage: This limit is useful for controlling the total memory footprint of a process, including both RAM and disk space
  • Key Differences:
    • Scope: Private Memory is limited to physical RAM, while Virtual Memory includes both RAM and disk space
    • Impact: Private Memory Limit directly affects the physical memory usage, whereas Virtual Memory Limit controls the overall memory reservation, including paging
    • These limits help manage resources efficiently and ensure the stability and performance of web applications hosted on IIS.
  • Settings:
    • So private limit can be 1 - 4 GB whereas the virtual limit might be 4 - 8 GB depending on the available ressources. However, a higher limit will hide possible memory leaks as the App Pool will be recycled later.
• Queue length
  • • As a thumb rule set 4000
• Overlapping recycle
  • • Enable overlapping recycle

In addition, not all settings should be changed in one go.

Proceed slowly and step by step to check the performance improvement.

Perhaps start with CPU and virtual/private memory and time-based recycling first. Then adjust the other settings.