ASP.NET Stability
St. Louis .NET Users Group
April 25, 2005
Preston Page
What’s Great About .NET
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Advanced Language Options
Extensive Framework for Windows,
Web and Device Programming
Greatly Improved Productivity
Enhanced Performance
Simplified Deployment
Best Stability Yet
When Stability Fails…
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End User Experience Suffers
Poor First Impression
Lost Credibility
Lost Opportunity
Lost Revenue
Increased Support Costs
Increased Operations Costs
Panic Mode, Escalations
Costly Rewrite
Six Stability Threats
1.
2.
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4.
5.
6.
Improperly Structured Error
Handling
“Hidden” Memory Leaks
Non-Compliance with Coding
Standards
Poor Performance
Database Issues
Inadequate Testing
Improper Error Handling
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Cause of 80 – 90 % of Stability Problems
Missing Altogether?
Empty Catch Statement
Too Much Faith in Garbage Collection
No Finally Statement
Objects Out of Scope for Finally
Inadequate Object Cleanup
Missing Logging/Alerting
Recursion from Catch Statement
Style Problems
Anatomy of Try…Catch
Try
' Starts a structured exception handler.
' Place executable statements that may generate
' an exception in this block.
Catch [optional filters]
' This code runs if the statements listed in
' the Try block fail and the filter on the Catch
' statement is true.
[Additional Catch blocks]
Finally
' This code always runs immediately before
' the Try statement exits.
End Try
' Ends a structured exception handler.
MSDN Help Sample
Function GetStrings (ByVal FileName As String) As Collection
Dim Strings As New Collection
Dim Stream As System.IO.StreamReader
Stream = System.IO.File.OpenText(FileName)
Try
While True
Strings.Add(Stream.ReadLine())
End While
Catch eos As System.IO.EndOfStreamException
' No action is necessary; end of stream
Catch IOExcep As System.IO.IOException
‘ Unexpected IO Error
Strings = Nothing ' Caller must test Null
Finally
Stream.Close
End Try
Return Strings
End Function
Subtle Problems…
Function GetStrings (ByVal FileName As String) As Collection
Dim Strings As New Collection
Dim Stream As System.IO.StreamReader
Stream = System.IO.File.OpenText(FileName) (1) ‘ Scope
Try
While True
(2) ‘ Deliberate Infinite Loop
Strings.Add(Stream.ReadLine())
End While
Catch eos As System.IO.EndOfStreamException (3) ‘ Empty
' No action is necessary; end of stream
Catch IOExcep As System.IO.IOException
‘ Unexpected IO Error
Strings = Nothing ' Caller must test Null
Finally (4)
Stream.Close
End Try
Return Strings (5) ‘ May Not Be Called
End Function
Improvements
Function GetStrings(ByVal FileName As String) As Collection
Dim Strings As New Collection
Dim Stream As System.IO.StreamReader
Try
Stream = System.IO.File.OpenText(FileName) (1)
Do While Stream.Peek() >= 0 (2)
Strings.Add(Stream.ReadLine())
Loop
Catch e As System.Exception (3)
LogException(e)
Strings = Nothing ' Caller must test Null
Finally (4)
Stream.Close()
GetStrings = Strings (5)
Stream = Nothing
Strings = Nothing
End Try
End Function
Hidden Memory Leaks
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Do Not Immediately Cause Errors
Usually Pass Code Scans/Reviews
Many Are Not Well Documented
Luckily, Existence Can Be
Determined by Load Testing
Ten Ways To Leak Memory
1.
2.
3.
Improper Structured Error Handling
Implicit ADO/ADO.NET Connections
Never Close Under Load
Failure to call Server.Clear when
trapping errors in
Application_OnError causes a
memory leak and WP resets
Ten Ways To Leak Memory
4.
5.
6.
Calling a delegate function with
BeginInvoke() without calling a
matching EndInvoke()
Failure to Set Objects to Null Or
Nothing
Passing or setting an open ADO
Connection object to a Property
Ten Ways To Leak Memory
7.
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Use of Response.Redirect in a Catch
Statement leaves threads open,
severely limits performance
Calling Transactional COM+
Components from ASP.NET
Failure to Close Database or Stream
Objects
Ten Ways To Leak Memory
10.
Failure to Properly Dispose of COM
Interop and .NET COM Wrapper
Objects Like:
System.EnterpriseServices (COM+)
System.DirectoryServices (ADSI)
Coding Standards Compliance
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Standards Embody Time Tested Best
Practices To Keep You Out Of Trouble
Compliance Reduces Support and
Maintenance Costs
Avoid Common Structural Defects
Use FXCop To Scan Code
Adapt Rules To Particular Needs
FXCop Demo
http://www.gotdotnet.com/team/fxcop/
FXCop Stability Rules*
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Library design*
Localization
Interoperability*
Mobility
Portability
Naming conventions
Performance*
Security*
Usage*
Performance Problems
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Cause Error Conditions Under Load
Reduce Scalability
Increase Hosting Costs
Increase Support Costs
Poor End User Experience
Catch With Load/Stress Tests
Common Database Issues
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Structure Problems
Tuning “Opportunities”
Inefficient Data Access Code
Coding Standards Non-Compliance
Failure To Use Caching Options
Inadequate Maintenance
Catch With Load/Stress Tests
Test Methodology
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Test Driven Development (NUnit)
Regular Code/Design Review (XP)
Unit Testing (NUnit, custom harness)
Functional Tests (formal plan)
User Acceptance Tests
Integration Tests (QC Servers)
Load Test (ACT, LoadRunner)
Stress Test (ACT, LoadRunner)
Formal Load Tests
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Performed On Calibrated, Production
Class Servers
Used To Judge Impact To Shared
Web Environments
Use To Gate Deployment To Protect
Infrastructure From Performance And
Stability Problems
Usually Requires Operations
Involvement, Special Infrastructure
Also Helps Uncover Configuration
And Infrastructure Issues
Desktop Load Testing
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Baseline Performance To Gauge
Effectiveness Of Changes
Uncover Performance and Stability
Issues As Early As Possible
Uncover Costly Design Flaws Early
Cheap And Easy Insurance
ACT Demo
Application Center Test
Can Determine
 Load Induced Error
 Memory Leaks
 Poor Performance
 Database Issues
 End User
Experience
 Other Server
Impact
Cannot Determine
 Missing Structured
Error Handling
 Adherence to
Coding Standards
 Application
Architecture
 Functional Issues
Load Test Pass/Fail Criteria
Metric
Goal
RPS/% CPU
50 RPS / 70% CPU
% Committed Bytes
< 22%
Residual Memory
< 10 MB
Total Socket Errors
0
Total HTTP Errors
0
Time Outs
0
WP Restarts
0
Memory Slope
~0
Memory Problems
Machine.Config Tuning
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Reduce idleTimeout from “Infinite”
Adjust responseDeadlockInterval for
long running applications
Use <location/> Node To Enforce
Best Practices and Control DEV, QC
and PROD Settings
Machine.Config Threading
Configuration setting Default
Recommendation
maxconnection
2
12 * #CPUs
maxIoThreads
20
100
maxWorkerThreads
20
100
minFreeThreads
8
88 * #CPUs
minLocalRequestFree 4
Threads
76 * #CPUs
More Information
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MSDN.Microsoft.com
• Knowledge Base Articles
• Patterns & Practices
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www.ASP.NET
• Starter Kits
• Tools
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www.Gotdotnet.com
• FXCop
• Help & Samples
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Bibliography as Web Links
• Send email to Preston
Questions?
prestonpage@charter.net