Introductiontoasp netwindbgdebugging-100506045407-phpapp01

AHMET MİTHAT BOSTANCIMICROSOFT, GTSC

IIS /WEB DEVELOPMENT SUPPORTAHMET.BOSTANCİ@MİCROSOFT.COM

Introduction To Debugging ASP.NET applications with

WinDBG and Dump Analysis

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.

AGENDA

ASP.NET Debugging TechnicsWhat is WinDBGWhen are WinDBG and dump analysis useful?What are dump files?How to collect dump?Basic commandsToolbox & References

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

What is WinDBG

A GUI Debugger with commands.Part of Debugging Tools For WindowsUser 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.

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.

Debugging Scenarios

Slow performance Web site is responsive but slow.

Hang Web site is unresponsive.

Crash Exceptions

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.

When do we need WinDBG?

Hang / Performance Problems – ManuelWeb 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.

When do we need WinDBG?

CrashWeb 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.

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.

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.exeKernel mode dump: Snapshot of the kernel

memoryComplete memory dump: Snapshot of the

whole memory including kernel and user mode.

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.

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.

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...

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

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.

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.

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.

Symbol Files

Footprint information of functions in EXE or DLL files

Necessary to see useful information in dumps, such as callstacks or variables.

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.

Symbols and WinDBG

Symbol server http://msdl.microsoft.com/download/symbols

Setting symbol server in WinDBG srv*c:\symbols\public*http://msdl.microsoft.com/

download/symbolsSymbols are downloaded to the local folder

when needed.

Commands in WinDBG

WinDBG commands Mostly used in unmanaged debugging.

Extensions DLL files Command sets for specific debugging requirements

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?Family

ID=5c068e9f-ebfe-48a5-8b2f-0ad6ab454ad4&displayLang=en

Extract and copy to the WinDBG installation folder. Load from WinDBG:

.load psscor2

WinDBG and ASP.NET 2.0 dump analysis

Open dump fileCheck and set symbol serverLoad the PSSCOR2 extenstion

.load psscor2

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

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>

Toolbox

Debugging Tools For Windows (WinDBG and ADPlus) http://www.microsoft.com/whdc/DevTools/Debugging/

default.mspxDebug Diagnostic Tool v1.1

http://www.microsoft.com/downloads/details.aspx?FamilyID=28BD5941-C458-46F1-B24D-F60151D875A3&displaylang=en

ProcDump http://technet.microsoft.com/en-us/sysinternals/dd996

900.aspxPSSCOR2

http://www.microsoft.com/downloads/details.aspx?familyid=5C068E9F-EBFE-48A5-8B2F-0AD6AB454AD4&displaylang=en

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/windb

g_part1.aspxhttp://www.cengizhan.com/

Q & A

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