1. Introduction To Debugging ASP.NET applications with
WinDBG and Dump Analysis
AHMET MİTHAT BOSTANCI
MICROSOFT, GTSC
IIS/WEB DEVELOPMENT SUPPORT
AHMET.BOSTANCI@MICROSOFT.COM

2. SCOPE
 This is NOT a full dump analysis workshop.
 The goal is to introduce the dump analysis as one of
the ASP.NET 2.0 web application debugging technics
and introduce the tools that help to achieve this task.

3. AGENDA
 ASP.NET Debugging Technics
 What is WinDBG
 When are WinDBG and dump analysis useful?
 What are dump files?
 How to collect dump?
 Basic commands
 Toolbox & References

4. ASP.NET Debugging
 Old School Debugging
 Using Response.Write
 Mostly not useful in production
 Not useful in hang scenario
 Usful in development
 Useful in production if there is a repro
 Looks easy but not useful
 Debugging in VS.NET
 Good for debugging in development
 Useful in production with remote debugging / attaching to w3wp.exe
 Not useful in most production env. issues.
 Debugging with WinDBG
 Live debugging / attaching to w3wp.exe
 Offline debugging: Collecting dumps of w3wp.exe and analysing in
WinDBG

5. What is WinDBG
 A GUI Debugger with commands.
 Part of Debugging Tools For Windows
 User mode and kernel mode debugging.
 Its commands are mainly useful in unmanaged
debugging.
 Extensions are sets of commands to ease debugging.
 SOS and PSSCOR2 extensions for .NET debugging.

6. Debugging with WinDBG
 Offline debugging
 Collecting dump files with specific tools for different scenarios
 Analysing in WinDBG.
 Live debugging
 Attaching a process
 Using breakpoints, catching exceptions, dumping the process
out to a file, etc... when necessary.

7. Debugging Scenarios
 Slow performance
 Web site is responsive but slow.
 Hang
 Web site is unresponsive.
 Crash
 Exceptions

8. Exceptions and ASP.NET
Exceptions are important objects in debugging.
 First Chance exceptions
 Too many exceptions may cause high CPU.
 Second Chance
 Exceptions which are not handled
 Causes crash.
 First chance exceptions may cause w3wp.exe
crashes, if it is thrown in a background thread, such
as finalizer threads.

9. When do we need WinDBG?
Hang / Performance Problems – Manuel
 Web site is running slow / performance issues.
 Web site is leaking memory - ends with performance
problems, hang or crash.
 Web site is running with high memory but not not
leaking.
 Web site is running with 100% CPU.
 Web site is running with high CPU or CPU usage spikes.
 Web site is completely hung - Does not response any
(dynamic) requests.

10. When do we need WinDBG?
Crash
 Web site or a specific page / method is throwing
exceptions but not crashing the w3wp.exe process,
first chance exceptions.
 Web site is crashing - w3wp.exe is crashing. Second
chance exceptions.

11. When do we NOT need WinDBG?
 When there is an easier way for debugging, such as a
specific page / method is not functioning as expected
 In this case, debugging in VS.NET with a repro code might be
easier.
 «Page cannot be displayed» type issues.
 In this case, troubleshooting IIS or network side is the correct
approach.

12. Dump
A dump is a snapshot of a process (user mode) or a
snapshot of all of the memory in kernel mode.
 Usermode dump: Process specific, such as w3wp.exe
 Kernel mode dump: Snapshot of the kernel memory
 Complete memory dump: Snapshot of the whole
memory including kernel and user mode.

13. Types of Dump
 Minidump
 Contains only selected parts of the memory used by the
process.
 Fulldump
 Contains the full copy of the process memory. Size of the
fulldump is somewhat equal to the virtual memory used by the
process.
 This is the dump type we are interested in most of the times.

14. What a dump contains
 All the things in the memory of the process.
 Information about the objects in heaps, threads,
information about the callstack, stack memory, etc...
 Limited information about the dead objects which
are not garbage collected yet.

15. What a dump does NOT contain
 Other processes' information.
 What was the CPU or memory usage in time. It is
only a snapshot.
 Also: Minidump is the smallest in size and does not
contain some useful information such as stack
objects, local variables, etc...

16. Tools for collecting dumps
 ADPlus
 Part of Debugging Tools For Windows
 Command line
 adplus -hang -pn w3wp.exe
 adplus -crash –iis
 Debug Diagnostic Tool
 GUI based
 Easy to configure and use
 ProcDump
 Command line
 Specific for high CPU usage but can be used for collecting manuel dumps as well
 procdump.exe -c 80 -s 30 -n 5 -ma NNNN >procdump.log
 Task manager
 Can be used to collect manuel dump
 Right click and create userdump
 Only on Win 7 and Win 2008

17. 32bit vs 64bit
 If the process is 32bit then the dump should be taken
by the 32bit version of the related tools. The dump
should be opened with the WinDBG’s 32bit version.
 Same rule applies to 64bit process.

18. Which dump in which scenario?
 Web site is crashing / throwing exceptions
 Crash rule with Debug Diagnostic Tool, ADPlus
 Web site is slow, hanging, using high memory
 Manuel dump(s) with Debug Diagnostic Tool, ADPlus.
 Web site is using high CPU or CPU is spiking
 Manuel dump(s) with Debug Diagnostic Tool, ADPlus.
 ProcDump for CPU spikes
 Web site is leaking memory
 Manuel hang dumps.
 Memory leak rule created in Debug Diagnostic Tool.
 Full IIS dumps
 Manuel dump
 Collects dumps for all of w3wp.exe, all of dllhost.exe and inetinfo.exe
process.

19. How many dump files should I collect?
 Dump is a snapshot of the memory and does not
contain the process history.
 Most of the crash scenarios
 One crash dump is enough to start debugging and find the
reason of the crash.
 Performance, hang
 Consecutive dump files of the same process.
 For example taking three dumps of w3wp.exe, each are taken
one minute apart.

20. Symbol Files
 Footprint information of functions in EXE or DLL
files
 Necessary to see useful information in dumps, such
as callstacks or variables.

21. Private vs Public symbols
 Private symbols contain local variables, structure
type information, functions, source line no., etc...
 Public symbols are the stripped version of the private
symbols.

22. Symbols and WinDBG
 Symbol server
 http://msdl.microsoft.com/download/symbols
 Setting symbol server in WinDBG
 srv*c:symbolspublic*http://msdl.microsoft.com/download/
symbols
 Symbols are downloaded to the local folder when
needed.

23. Commands in WinDBG
 WinDBG commands
 Mostly used in unmanaged debugging.
 Extensions
 DLL files
 Command sets for specific debugging requirements

24. Extensions
 Copied to the WinDBG installation directory
 .NET related extensions
 SOS
 Comes with .NET framework
 PSSCOR2
 Superset of SOS
 .NET 2.0 specific extension
 http://www.microsoft.com/downloads/details.aspx?FamilyID=5c
068e9f-ebfe-48a5-8b2f-0ad6ab454ad4&displayLang=en
 Extract and copy to the WinDBG installation folder.
 Load from WinDBG:
 .load psscor2

25. WinDBG and ASP.NET 2.0 dump analysis
 Open dump file
 Check and set symbol server
 Load the PSSCOR2 extenstion
 .load psscor2

26. Some WinDBG commands
 Vertarget
 Shows information about the system on which you are debugging
 Lm
 Displays loaded module information
 ~
 Lists all OS threads
 ~Ns
 Switch to thread #N
 K
 Shows unmanaged call stack of the thread switched.
 .hh
 Opens help file
 .reload /f
 Forces to reload the symbols.
 !runaway
 Shows the thread’s CPU time

27. Some PSSCOR2 commands
 !DumpAllExceptions (!dae)
 Shows managed exceptions thrown.
 !DumpDataTables
 Shows data tables objects in memory. Useful when debugging memory issues.
 !DumpColumnNames (!dcn)
 Prints out the column names for a data table given.
 !ASPXPages
 Shows ASPX pages running on all threads.
 !threadpool
 Shows ASP.NET thread pool information including the requests in the queue and the current CPU usage of OS.
 !FindDebugTrue
 Shows the web applications running in debug mode.
 !FindDebugModules
 Shows the modules built in debug mode.
 !SaveAllModules (!sam)
 Saves the all modules in the process. Useful when using the reflector to get the code from dump file.
 !eeversion
 Prints the .NET framework version. Useful when checking the fixes or service packs installed.
 !help
 !help <command>

28. Toolbox
 Debugging Tools For Windows (WinDBG and ADPlus)
 http://www.microsoft.com/whdc/DevTools/Debugging/default.msp
x
 Debug Diagnostic Tool v1.1
 http://www.microsoft.com/downloads/details.aspx?FamilyID=28B
D5941-C458-46F1-B24D-F60151D875A3&displaylang=en
 ProcDump
 http://technet.microsoft.com/en-us/sysinternals/dd996900.aspx
 PSSCOR2
 http://www.microsoft.com/downloads/details.aspx?familyid=5C068
E9F-EBFE-48A5-8B2F-0AD6AB454AD4&displaylang=en

29. Refernces
 http://blogs.msdn.com/tess/ (İngilizce)
 http://blogs.msdn.com/amb/
 http://blogs.msdn.com/farukceliktr/
 http://blogs.msdn.com/cenkiscan/
 http://www.codeproject.com/KB/debug/windbg_pa
rt1.aspx
 http://www.cengizhan.com/

30. Q&A
?