Debugging Windows DNAbased ECommerce Applications Aaron Barth Technical Lead Solution Integration En

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Debugging Windows DNA-based E-Commerce
Applications Aaron BarthTechnical
LeadSolution Integration EngineeringMicrosoft
Corporation
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Objectives

• Help troubleshoot problems with Microsoft
  Windows Distributed interNet Applications (DNA)
  e-commerce applications by
• Understanding Web application architecture
• Identifying common support problems
• Mapping tools and techniques to solve common
  problems

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Web Application Architecture

• Types of Web requests
• HTM or image (static content)
• Served from disk
• ISAPI (dynamic content)
• Filters (DLL)
• Extensions (DLL)
• ASP (dynamic content)
• Interpreted script
• COM applications
• Compiled code (DLL or EXE)

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Windows DNA 2000 Web Architecture
IIS Pool Threads
ASPProcessorThreadMax (25 x CPUs)
SMTP
FTPSVC
W3SVC
Web Application Manager
Inetinfo.exe
Port 80
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Web Application Architecture

• Thread pools
• IIS pool threads
• Configured in registry
• PoolThreadLimit
• MaxPoolThreads
• ASP/COM worker threads
• Configured in the metabase
• ASPProcessorThreadMax
• COM worker threads
• Not configurable

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Isolation Levels

• IIS process
• Low isolation
• Default in IIS 4.0
• Pooled
• Medium isolation
• New defaultin IIS 5.0
• Isolated
• High isolation
• Existed in IIS 4.0

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IIS Process (Low)
IIS Pool Threads
ISAPI
Web Application Manager
SMTP
FTPSVC
W3SVC
Inetinfo.exe
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Pooled (Medium)
Dllhost.exe
Web Application Manager
Inetinfo.exe
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Isolated (High)
Dllhost.exe
Web Application Manager
Inetinfo.exe
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Advantages and Disadvantages
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Common Support Problems

• Crash
• Access violation
• Other exceptions
• Stop responding (hang)
• IIS hang
• ASP hang or ASP queuing
• Resource-related failures
• High CPU utilization
• Memory leak

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Application Crashes (Dev)

• Developer view
• Access violations
• Compiled code reads from or writes to memory that
  it does not have access to
• Other exceptions
• Divide by zero
• RPC server unavailable

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Application Crashes (Ops)

• Operational view
• IIS process
• Process dies or becomes unstable
• Services may restart
• Event is logged in the event log
• Dr. Watson dialog box
• Isolated/pooled/COM application
• Application is terminated and restarted on next
  request (JIT Activation)
• Event is logged in the event log
• All state (session/application/component) is lost

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Crashes IIS Process
IIS Pool Threads
X
ISAPI
Web Application Manager
SMTP
FTPSVC
W3SVC
Inetinfo.exe
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Crashes Pooled And Isolated
Dllhost.exe (1)
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ISAPI
Web Application Manager
Inetinfo.exe
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DEMO Crash
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Application Hangs (Dev)

• Developer view
• IIS hang
• Thread blocking
• Existing threads performing long running
  operations
• No more threads available
• ASP hang
• All ASP/COM threads are busy
• No more threads can be created
• ASP request queue is full

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Application Hangs (Ops)

• Operational view
• IIS hang
• HTM or static file requests hang
• Cannot connect to Web server
• ASP hang
• ASP?Requests executing counter is close to or
  equal to ASProcesssorThreadMax x number of CPUs
• ASP?Requests queued is gt0 for an extended period
  of time
• ASP pages do not return data, but static content
  can be served

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DEMO Hang
Dual processor computer ASProcessorThreadMax
25 25 x 2 50 requests executing
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Resource Related Failures (Dev)

• Developer view
• High CPU utilization
• Code running a thread or threads runs into a
  tight loop and does not yield CPU time
• Low memory conditions
• Processes or DLLs allocate memory that is not
  freed
• Processes or DLLs starve the operating system of
  resources by using all available memory
• Processes or DLLs use handles without closing
  them (leak)

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Resource Related Failures (Ops)

• Operational view
• High CPU utilization
• Processor?ProcessorTime is close to 100
• Process? ProcessorTime ? inetinfo.exe or
  dllhost.exe is close to 100
• All server operations seem sluggish
• Low memory conditions
• Events logged to the event log
• Memory? Available bytes decreases
• Process? Private bytes ? inetinfo.exe or dllhost
  increases
• All server operations seem sluggish

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DEMO CPU Utilization
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Diagnostic/Debugging Tools

• Exception monitor
• User mode process dump
• Service
• Manual dump
• Windows Debugger (WinDBG)

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DEMO Exception Monitor
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Exception Monitor

• Advantages
• Lightweight, quick and easy to use
• Great for isolating down to the DLL that is
  causing the problem
• Disadvantages
• Sometimes not enough information
• If symbols are wrong can be misleading
• Where to get it?
• http//msdn.microsoft.com/workshop/server/iis/ixc
  ptmon.asp
• (Note that the URL should be entered as one
  line it is wrapped here for readability.)

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DEMO User Mode Process Dump
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User Mode Process Dump

• Advantages
• Provides a process snapshot at the time the dump
  is created
• All information about a crash is in the dump file
  (parameters, modules, threads)
• Disadvantages
• Dump file can be large if process has a large
  memory footprint
• Need symbols to be correct when reading the dump
  file
• Dump snapshot does not show history (before crash
  etc.)
• Where do I get it?
• http//www.microsoft.com/downloads/release.asp?Re
  leaseID17805
• (Note that the URL should be entered as one
  line it is wrapped here for readability.)

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DEMO Windows Debugger
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Windows Debugger (WinDBG)

• Advantages
• Powerful lightweight debugger
• Can perform source level debugging
• Can read dump files (.dmp)
• Excellent symbol support
• Disadvantages
• Not well known
• GUI application that can be slower than
  command-line debuggers
• Windows 2000 Customer Diagnostics and Support
  Tools CD

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Mapping The Tools To The Problems

• Isolate problem
• Run Exception Monitor
• View .dbl file with Log File Analyzer
• Run UserDump as a service
• Analyze .dmp file with Windows Debugger

Crash
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Mapping The Tools To The Problems

• Isolate problem
• Run emcmd /p
• Run Userdump.exe against each process ID from
  step 2 Inetinfo.exe
• Analyze .dmp files with Windows Debugger

Hang
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