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Advanced Troubleshooting
with Debug Diagnostics on
IIS 6
Draft 2.5 5/13/06
Name
Title
Group
Microsoft Corporation
Agenda
Introduction
A look at Debug
Diagnostics
Dig into crash scenarios
Understanding hangs
Investigating memory leaks
Session Summary
Introduction
Overview of Debugging:
Past and Present
Integral tools for resolving
Debug scenarios
Variables impacting
Debugging
Overview of Debugging
Past and Present
Past: offered many tools, fewer resolutions
Previous tools were often not server-ready
No single tool to address different debugging scenarios
Required expertise in debugging
Present: more advanced tools, still timeconsuming to solve
Still lacks any analytical piece
Existing tools are not “integrated” into single tool
Do you really want to learn “debugging?”
Talking about tools…
There are several tools designed at
resolving the same problems
As Windows Servers have grown, so
have the debugging tools
Example of debugging tools
Exception Monitor
ADPlus.vbs (i.e. – cdb.exe)
IIS Debug Toolkit 1.1
IIS State
Variables Impacting
Debugging (2)
IIS’s Extensibility Examples
ISAPI
ASP.NET
Active Server Pages (ASP)
COM components
PHP (ISAPI)
Perl (CGI or ISAPI)
Oracle\MySQL
Ever felt like this?
These “extensible” parts are often
integrated and executing in same process
Debug Diagnostics 1.0
“Core” pieces of DebugDiag
Understanding “Rules”
Using DebugDiag’s User
Interface
Core pieces of Debug Diag
3 pieces make up Debug Diag 1.0
Service
Host (also called Controller)
User Interface
DbgSvc.exe
DbgSvc.exe
DebugDiag.exe
Core pieces of Debug Diag
The Service – DbgSvc.exe
Service is multipurposed
Interacts with the
Debugger Host
Allows:
Service required to
attach invasively to
process
To run from
Terminal Services
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
Core pieces of Debug Diag
The Host – DbgHost.exe
Host
Where the
DbgEng.dll
instance is loaded
Exposes 3 classes
DbgSvc.exe
Attac
h
DbgHost.exe
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
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
DebugDiag.exe
Control
Scripts
DbgHost.exe
Crash Scenarios
Background of crashes
Using DebugDiag to
quickly identify root
cause of crashes
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
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
Debugging Crashes
with Debug Diagnostics:
Crash Rule
Name
Title
Group
Hang Scenarios
Investigating the
theory of
“process hangs”
Using DebugDiag to
debug “process
hangs”
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
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
What are
common thread
pools for IIS?
ATQ thread pool
ASP thread pool
ASP.NET thread pool
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
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
IIS
Thread
4
1
SQL
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
Debugging Deadlocks and
Process Hangs with
DebugDiag: Hang Rule
Name
Title
Group
Looking into Leaks…
What is a leak?
Types of Leaks
Debugging a Leak
with Debug
Diagnostics
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
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
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
Nailing a Memory Leak in a
Web Application using
DebugDiag: Memory Rule
Name
Title
Group
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
Know what DebugDiag can do…and also what it can’t do
Debug Diagnostics 1.0 web
resources
http://www.microsoft.com/windowsserver20
03/iis/diagnostictools/default.mspx
© 2005 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.