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Advanced Troubleshooting with Debug Diagnostics on IIS 6

Advanced Troubleshooting with Debug Diagnostics on IIS 6. Chris Adams Program Manager IIS Product Unit Microsoft Corporation. Agenda. Debug Diagnostics 1.0 Dig into crash scenarios Understanding hangs Investigating memory leaks Session Summary. Debug Diagnostics 1.0.

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Advanced Troubleshooting with Debug Diagnostics on IIS 6

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  1. Advanced Troubleshooting with Debug Diagnostics on IIS 6 Chris Adams Program Manager IIS Product Unit Microsoft Corporation

  2. Agenda • Debug Diagnostics 1.0 • Dig into crash scenarios • Understanding hangs • Investigating memory leaks • Session Summary

  3. Debug Diagnostics 1.0 • “Core” pieces of DebugDiag • Understanding “Rules” • Using DebugDiag’s User Interface

  4. Core pieces of Debug Diag • 3 pieces make up Debug Diag 1.0 • Service • Host (also called Controller) • User Interface DebugDiag.exe DbgHost.exe DbgSvc.exe

  5. Core pieces of Debug Diag The Service – DbgSvc.exe • DbgSvc.exe • To register the service: • C:\DebugDiag> DbgSvc /service • To start the service: • C:\DebugDiag> net start DbgSvc • To stop the service • C:\DebugDiag> net stop DbgSvc • Unregister the service • C:\DebugDiag> DbgSvc /unregserver • Service is multi-purposed • Interacts with the Debugger Host • Allows: • Service required to attach invasively to process • To run from Terminal Services

  6. Attach DbgSvc.exe DbgHost.exe Core pieces of Debug Diag The Host – DbgHost.exe • Host • Where the DbgEng.dll instance is loaded • Exposes 3 classes DbgControl: Attach/Detach from processes or open/analyze a memory dump DbgObj: Collect process or memory dump information Manager: Mainly to output analysis data to the report file

  7. DebugDiag.exe Core pieces of Debug Diag The User Interface – DebugDiag.exe • User Interface designed to simplify: • Rule creation • View processess • Initiate analysis of memory dumps • Add analysis scripts • Change properties for Debug Diag Control Scripts DbgHost.exe

  8. Crash Scenarios • Background of crashes • Using DebugDiag to quickly identify root cause of crashes

  9. Background: Exceptions • What is an exception? • How do applications cause exceptions • What is a “handled” exception? • Unhandled exceptions need debugging and resolution Access Violation: C000 0005 Breakpoint Exception: 8000 0003 Stack Overflow: C000 00FD C++ exception: E06D7363 Managed exception: E0434F4D Invalid Handle: C000 0008

  10. Background: Heap (2) • What is a heap? • Heap is a data structure • Heap Corruption: • Certain rules must be followed when using the heap • When rules are violated, heap corruption occurs • Heap corruption crashes • Code that corrupts heap is usually not the ones impacted

  11. Debugging Crasheswith Debug Diagnostics:Crash Rule Chris Adams Program Manager IIS Product Unit

  12. Hang Scenarios • Investigating the theory of “process hangs” • Using DebugDiag to debug “process hangs”

  13. Theory of “Process Hangs” • What is a process? • Memory boundary for execution of code • Allocated by Operating System done by calling CreateProcess or CreateProcessAsUser API • Processes do not execute code • Contains a minimum of 1 thread • What is a thread? • An independent sequence of instructions executing within a process

  14. What are common thread pools for IIS? • ATQ thread pool • ASP thread pool • ASP.NET thread pool Theory of “Process Hangs” • Thread implications on applications • The level of concurrency (virtual) is dictated by the number of threads • Real concurrency is dictated by the number of execution units • 1 processor = one or more execution units

  15. Runaway Threads • A runaway thread is a thread stuck in a infinite (or near) loop • Performing a task that is consuming CPU • Either by design or because of error conditions • Runaway thread is taking CPU resources away from other threads • Often takes away from good threads • Causes performance degradation for server

  16. SQL IIS Defining a Blocked Thread • A thread that isn’t using any CPU resources • Waiting on database calls to return • Waiting on web service calls to return • Waiting on a socket/network call to return • Waiting on a lock Thread 3 Thread 4 Thread 1

  17. Locks and Deadlocks • What is a lock? • A synchronization mechanism to protect resources from being corrupted due to simultaneous access by multiple threads • Why do developers use locks? • Protecting data • Protecting other resources that are not memory based • Impact on applications if locks are poorly implemented • Causes threads to block • Can cause deadlock situations when using multiple locks in the application • Process hangs when no threads are available

  18. Debugging Deadlocks and Process Hangs with DebugDiag: Hang Rule Chris Adams Program Manager IIS Product Unit

  19. Looking into Leaks… • What is a leak? • Types of Leaks • Debugging a Leak with Debug Diagnostics

  20. Leak Scenarios (2) • Why are leaks difficult to identify and resolve? • Server applications often cache memory allocations • The allocations are long term • These applications, to outsiders, look to have memory leaks • There are many other caches • Using Performance Monitor and seeing memory growth does not equal a memory leak

  21. Leak Scenarios (3) • What are short-term allocations? • Memory expensive applications use “spike” allocations but are destroyed immediately after request (not long- sustaining) These are not Memory Leaks

  22. Leak Scenarios (4) • Difference between cache and memory leaks? • Memory leaks are caused by unbounded allocations • Cache memory usage rises quickly, but tops out after application is stabilized

  23. Nailing a Memory Leak in a Web Application using DebugDiag: Memory Rule Chris AdamsProgram Manager IIS Product Unit

  24. Session Summary • Debugging Live Web Applications without downtime is challenging • Crashes cause processes to terminate due to unhandled exceptions • Hangs are caused due to race conditions, lock contention, network blocking, database blocking, infinite loops and deadlocks • Leaks are caused by the failure to release memory allocated beyond typical short term allocations and caching • Debug Diagnostics has an extensibility model that allows it to successfully capture and analyze common debugging scenarios to determine the root cause

  25. Debug Diagnostics 1.0 web resources • http://www.iisdiagnostics.com

  26. © 2005 Microsoft Corporation. All rights reserved. This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.

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