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Off-Cpu

OpenResty XRay Aug 14, 2026

OpenResty XRay Updated Aug 14, 2026 11 mins read

Off-CPU Analysis: Four Root Causes Behind Low CPU Yet High Latency

openresty-xray off-cpu tutorial
  • What Is Off-CPU Time?
  • The Symptom: CPU Usage Won’t Climb, Yet Requests Are Queuing
  • Four Categories of Off-CPU Root Causes with Real-World Root-Cause Chains
  • How to Quantify Off-CPU Time
  • On-CPU + Off-CPU = Wall-Clock Time: The Bigger Picture and the Tool Ecosystem
  • FAQ
  • What Is Off-CPU Time?
  • The Symptom: CPU Usage Won’t Climb, Yet Requests Are Queuing
  • Four Categories of Off-CPU Root Causes with Real-World Root-Cause Chains
  • How to Quantify Off-CPU Time
  • On-CPU + Off-CPU = Wall-Clock Time: The Bigger Picture and the Tool Ecosystem
  • FAQ

OpenResty XRay Aug 12, 2026

OpenResty XRay Updated Aug 12, 2026 4 mins read

Nginx Reverse Proxy QPS Dropped 15x: A Missing upstream keepalive and an -O0 Debug Build

openresty-xray casestudy lua nginx off-cpu
  • A 15x Slower Nginx Reverse Proxy β€” and No Errors in the Logs
  • Flame Graphs Expose a Connection Storm: The Missing upstream keepalive
  • The Remaining 10% Gap: Baseline Comparison Points to the Compiler
  • How an -O0 Debug Build Cost Us 10% of Performance
  • A 15x Slower Nginx Reverse Proxy β€” and No Errors in the Logs
  • Flame Graphs Expose a Connection Storm: The Missing upstream keepalive
  • The Remaining 10% Gap: Baseline Comparison Points to the Compiler
  • How an -O0 Debug Build Cost Us 10% of Performance

OpenResty XRay Aug 14, 2026

OpenResty XRay Updated Aug 14, 2026 9 mins read

The Nginx Worker That Refused to Serve More Than 300 RPS: Traced to a 75ms Event-Loop Block

openresty-xray casestudy lua nginx off-cpu
  • High Load but No Useful Work: CPU Contention from a Missing worker_cpu_affinity
  • How Blocking Lua I/O Calls Halted the Nginx Event Loop
  • Measuring File I/O Latency: Up to 1.5ms per Call
  • How Bad Was the Nginx Event-Loop Blocking? 43,952 Samples, a 75ms Worst Case
  • Frequently Asked Questions
  • High Load but No Useful Work: CPU Contention from a Missing worker_cpu_affinity
  • How Blocking Lua I/O Calls Halted the Nginx Event Loop
  • Measuring File I/O Latency: Up to 1.5ms per Call
  • How Bad Was the Nginx Event-Loop Blocking? 43,952 Samples, a 75ms Worst Case
  • Frequently Asked Questions

OpenResty XRay Aug 14, 2026

OpenResty XRay Updated Aug 14, 2026 6 mins read

Perl Process Stuck at 13% CPU: Off-CPU Flame Graphs Pinpoint a Blocking HTTP Call

tutorial openresty-xray perl off-cpu
  • The symptom: Perl process CPU usage stays low under heavy requests
  • Find the blocking Perl code paths with OpenResty XRay’s off-CPU flame graphs
  • Automatic analysis and reports in the Insights page
  • FAQ
  • What is OpenResty XRay
  • About The Author
  • The symptom: Perl process CPU usage stays low under heavy requests
  • Find the blocking Perl code paths with OpenResty XRay’s off-CPU flame graphs
  • Automatic analysis and reports in the Insights page
  • FAQ
  • What is OpenResty XRay
  • About The Author

OpenResty XRay Aug 14, 2026

OpenResty XRay Updated Aug 14, 2026 6 mins read

Python Process Stuck at 8% CPU: Off-CPU Analysis Traces a Blocking subprocess.run Call

tutorial openresty-xray python off-cpu
  • The symptom: Python process CPU usage stays low under heavy requests
  • Find the blocking Python code paths with OpenResty XRay’s Guided Analysis
  • Automatic analysis and reports in the Insights page
  • FAQ
  • What is OpenResty XRay
  • About The Author
  • The symptom: Python process CPU usage stays low under heavy requests
  • Find the blocking Python code paths with OpenResty XRay’s Guided Analysis
  • Automatic analysis and reports in the Insights page
  • FAQ
  • What is OpenResty XRay
  • About The Author
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