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Mark FriedmanDemand Technology Software
[email protected]://computerperformancebydesign.com
Monitoring Web Application Response
Times in Windows
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Why is this web app running slowly?
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Main Topics
Building scalable web applicationsYSlow scalability model of web page compositionPage Load Time and Round tripsLimitations of the approach
W3C Nav/Timing APIGoogle Analytics & RUM
Progress report on an ETW-based approach to web application performance monitoring
plus, sprinkle in some case studies & best practices
Presentation Outline
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Themes:The Value of Response Time measurements
Service Level reporting Application response time measurements correlate with measures of customer
productivity & satisfaction
Queuing models, decomposition & other analytic techniques
Obstacles: Measurement data missing from standard Windows ASP.NET counters, but it is available
from other sources Request-Response boundaries are blurred in many AJAX applications Understanding how to set good response time objectives
Since human beings are adaptable & “ Good” and “Bad” are often relative to the application context See “Engineering Time,” by Dr. Steve Seow
Web Application Performance
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Themes:Web application programming models and fashion change faster than
tools can adaptAJAX
e.g., Auto-complete in Google Search achieved using client-side Javascript & Asysnchronous Http web service Requests
High Availability and Scalability using n-tiered architectures typically, a Presentation Layer, Business Objects layer, and a Data Access Layer
HTML5HTTP/2
Effective performance tools are usually one or two generations behind emerging technology e.g., http://webpagetest.org
Web Application Performance
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Fundamental concept in software performance engineering (SPE)
namely, f(x), such that f(x) reliably predicts Response time.
Factors can be linear (m+n…)multiplicative (m * n)exponential (mn)
Scalability models
Assuming rendering time inside the web client is minimal,
Web Page Load Time = Render Time RoundTrips * RTT
where
RoundTrips =
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YSlow scalability model
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Why is my web app running slowly?
Part 1.
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Case Study.
Developed using ASP.NET (Server-side controls)Multiple tiers: presentation/business objects/data layer
Uses the Model-View-Controller (MVC) pattern
Key elements of the web Pagedata-rich Charting component (.NET Chart, based on the Dundas component)Chart definition used to generate the PDB Query and the results are mapped
to a Chart instance Library of Chart templates Machine selection Date/Time selection
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Why is this web app running slowly?
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Example:
Ask YSlow
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Why is this web app running slowly?
Based on the influential work of Steve Souders*originally at Yahoosince migrated to Google
Google Chrome extensionRule-based Influenced:
Chrome PageSpeed Insights IE Developer ToolsFiddlerGlimpseetc.
* High Performance Web Sites, O’Reilly Media, 200712
What is YSlow?
Optimize for Page Load Time Request.Start DOM.Complete
Make specific recommendations on how to improve Page Load Time for a specific web pageInventorying the Document Object Model (DOM) after the composition & rendering
the of web page: Calculate # of Http objects and their size
Does not attempt to actually measure Page Load Time, however.
Lead to a standardization effort to wire performance timing data to the DOM & create a consistent way to access it
Navigation Time, Performance Timing & a High Resolution Clock
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What is YSlow?
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Page Load Time
Web Browser Http Server
Http GET Request (Uri)
Compose&
Render
Http RESPONSE
Note: Http is a sessionless protocol
Measurement techniques
• sniff network packets• monitoring service to
submit synthetic Requests• Real User Measurements
• attach handlers to DOM window.unload and window.load events
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YSlow Chrome extension
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Chrome PageSpeed
Response message often contains embedded references to additional resources needed to render the Page
e.g., image files style sheets javascript files 17
Page Load Time
Web Browser Http Server
Http GET Request (Uri)
Compose & Render
Http RESPONSE
HTTP interacts with the underlying TCP/IP networking protocols HTTP Response messages > Ethernet packet size (~ 1500
bytes) require multiple IP packets With large cookies and a large number of parms, GET Request
messages can even exceed the Ethernet packet size 18
Page Load Time
Web Browser Http Server
Http GET Request (Uri)
Compose & Render
Http RESPONSE
YSlow scalability model:
assuming web client processing time is minimal, then
Render Time RoundTrips * RTT
RoundTrips =
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Page Load Time
Ask YSlo
w
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Why is this web app running slowly?
YSlow scalability model:Browser Render Time RoundTrips * RTT
Web Browser performs page composition using the Document Object Model, or DOMYSlow Rule: Make fewer HTTP requestsYSlow Rule: Improve cache effectivenessYSlow Rule: Reduce the number of DOM elementsYSlow Rule: Compress the objects the page does need to load
Tuning is a process that attempts to drive # RoundTrips 1
RoundTripTime 0 21
YSlow Scalability model
YSlow never actually measures RTT, but other related tools can
RTT may vary across RequestsObjects can be geographically dispersed
Local cluster, remote, cloude.g., referencing 3rd-party, advertising services
TCP adaptive window scaling and other network congestion avoidance strategies
Ignores variability in the execution time of client and server-side codee.g., sort() a large list of elements, ora hi-res visualization component that scales nonlinearly with the size of the result set
Compression recommendations can be at odds with good code maintainability practices
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YSlow Scalability model complications
Web Browsers create multiple TCP sessions to download referenced objects in parallelYSlow Rule: take advantage of parallel sessions by loading scripts last
Accurate rendering of the DOM requires that downloading a Javascript file blocks parallel downloadsScript may add elements to the DOM dynamically, call other scripts or reference
additional resources Browser assumes DOM rendering can only resume after the Javascript code
executes
Page Load Time = Browser Render Time +Script execution Time + (RoundTrips * RTT)/Sessions
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YSlow Scalability model complications
Despite the many complications, the YSlow scalability model has proved very influentialBrowser Page Load Time is an end-to-end measurement of service
time, which is apt to be correlated with customer satisfaction
see, for example, http://www.slideshare.net/Strangeloopnet/37-lessons-ive-learned-on-the-performance-front-lines
Inspired development of related tools to measure Page Load Time
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YSlow Scalability model
The YSlow scalability model is useful, but it is not adequate for many web applications
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Case study: YSlow scalability model assessment
Page Load time is a measure of end-to-end response timeNavigation Timing measurements decompose overall
response time into Network, Server, and Client (i.e., web browser) components
YSlow is silent: the scalability of server-side componentsthe diversity of web client hardware (PCs, tablets,
phones) & software (iOS, Android, Windows)the performance of the client’s network connection
e.g., Internet vs. Intranet connections
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YSlow Scalability model assessment
Despite the many complications, the YSlow scalability model has proved very influential
Sparked a standardization effort so Javascript developers could access the PLT measurements reliably across Browsers
Creation of standard DOM performance objects that are accessible to Javascript
Finally, now that actual web application performance data is available in the web browser, how do I get that data back to my data center for optimization & capacity planning?
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YSlow Scalability model
28Standard DOM NavTiming object
Prompt for unload redirect App
cache DNS TCP Request Response Processing load
unload DOMContentLoaded
navigationStartredirectStart
redirectEnd
fetchStartdomainLookupStart
domainLookupEnd
connectStartsecureConnectionStart
connectEndrequestStart
responseStartresponseEnd
loadEventStartloadEventEnd
unloadEventStartunloadEventEnd
domLoadingdomInteractive
domContentLoadedEventStartdomContentLoadedEventEnd
domComplete
Http Request/Response and Rendering eventsWeb Performance Working GroupPerformance Timeline, Navigation Timing,
and High Resolution Time specs Supported in IE, Chrome, WebKit, and FoxFire
Event timings can be used to calculate:
Network latency (from the standpoint of the web client) Page Render time (once the page components are
received from the server) Entire sequence from navigation to page load completion:
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Page Load Time Measurements
Navigation Timing spec: https://dvcs.w3.org/hg/webperf/raw-file/tip/specs/NavigationTiming/Overview.html#processing-model
Calculate network latency: responseEnd - fetchStart
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Page Load Time Measurements
Calculate Page Render Time:loadEventEnd - responseEnd
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Page Load Time Measurements
Calculate entire sequence: loadEventEnd - navigationStart.
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Page Load Time Measurements
see https://developer.mozilla.org/
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performance.now High Resolution Clock
<html> <head> <script type="text/javascript"> // Add load event listener. window.addEventListener("load", loadTime, false);
function loadTime() { // Get current time. var now = window.performance.now(); // Calculate page load time. var page_load_time = now - performance.timing.navigationStart; // Write the load time to the F12 console. if (window.console) console.log(page_load_time); } </script> </head><body> <!- Main page body is here. --> </body> </html>
Now that actual web application performance data is available in the web browser, how do I get that data back from the web client?What about the volume of measurement data that requires processing
& analysis?
Google Analytics uses web beacons to send the response time data to Google’s data center for analysis and reporting
Yahoo Boomerang project can be used to send web beacons with the data back to your data center
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NavTiming API
Architecture of an ASP.NET applicationWindows OSTCP/IP(Clustered) IIS front end Web ServersASP.NET.NET CLRADO.NET (data layer)
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Why is my ASP.Net app running slowly?
Dynamic HTML is session-oriented behavior layered on top of the HTTP
Web applications require state Who you areWhere you are (mobile apps)
They preserve state:During a session
TCP protocol is session-orientedRequires a connectionCalculates RTT per connection (used in re-try logic)
Between sessions (using cookies, etc.)
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ASP.NET Application Architecture
Server-side Request processingEvent-oriented programming model (Postback)HttpContext wrapper around the HTTP RequestPersistent State
ViewStateSession StateApplication and Page Cache objectsetc.
ASP.NET Application Performance
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IIS Architecture
User
Kernel
HTTP
TCP
IP
Network Interface
HTTP Kernel Mode Driver
(http.sys)
HTTP Response Cache
(Physical Memory)
LSSAS
WindowsAuthentication
SSL
Inetinfo
IIS Administration
FTP
Metabase
SMTP
NNTP
SVCHOST
W3SVC
W3wpW3wp
Mscoree.dll
http
<code-behind>.dll
Default.aspx
Application Pool
W3wpW3wp
Mscoree.dll
<code-behind>.dll
Default.aspx
Application Pool
WAS
Cache
net.tcp net.tcp
http
HttpApplication Event Handlers (IHttpModule)
IIS 7.0 Integrated Mode (pipeline)
Event EventBeginRequest PreRequestHandlerExecuteAuthenticateRequest PostRequestHandlerExecutePostAuthenticateRequest ReleaseRequestStateAuthorizeRequest PostReleaseRequestStatePostAuthorizeRequest PostMapRequestHandlerResolveRequestCache PostMapRequestHandlerPostResolveRequestCache PostMapRequestHandlerMapRequestHandler UpdateRequestCachePostMapRequestHandler PostUpdateRequestCacheAcquireRequestState LogRequestPostAcquireRequestState EndRequest
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Extends the ASP.NET event model to all Http RequestsHttpApplication Event Handlers (IHttpModule)
IIS 7.0 Integrated Mode (pipeline)
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public class BoomerangBeacon : IHttpModule { public MyHttpModule() {} public void Dispose() {} public void Init(HttpApplication application) { application.BeginRequest += (new EventHandler(this.Application_BeginRequest)); }
}
w3wp.exe
Common Language Runtime (CLR)JIT compilerGarbage Collection threads
mscoree.dllmscorsvr.dllMyApp.dll
ASP.NET Application Architecture
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Many, many Windows components are instrumented with ETWKernel objects include disk IO, process,
thread, paging, CPU TCP/IP, HttpServer, CLR
Providers may issue a current status Rundown
CallStacks can be captured
Event correlation:CPU ID, Process ID, Thread ID, File
Handle, Tcp Session ID (Port)42
ETW: Event Tracing for Windows
Many obstacles to using trace-based instrumentation effectively in performance investigationsSheer volume of trace data that can be generated (e.g., OS Dispatcher
ContextSwitch events) Cannot always be filtered effectivelyVery little documentation on specific events and how they are logically related
Inconsistent semantics (but only a few common patterns)Sequence: Begin, Step, EndStateChange(oldState, newState)Fork:JoinSend:Receiveetc.
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ETW: Event Tracing for Windows
Resource MonitorWindows Performance tools (aka xperf) VS Profiler’s Concurrency Visualizer
inspired by Rico Mariani’s ETLStackBrowser programleveraged Vance Morrison’s TraceEvent .NET libray
and, introducing the Web Application Trace ExplorerGathers, analyzes, filters & reports on server-side events from TcpIP,
HttpServer, and instrumented application Scenarios, plus Boomerang Beacon data from web clients
Designed to help explore the semantics of these sparsely documented event streams 44
ETW tooling
IHttpModule to intercept the Boomerang beacon requests and turn them into ETW events
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ETW tooling private void Application_BeginRequest(Object source, EventArgs e){
// Create HttpApplication and HttpContext objects to access // request and response properties.
HttpApplication application = (HttpApplication)source;HttpContext context = application.Context;
string beaconUrl = GetBeaconUrl(); // Helper routine for
beacon url string filePath = context.Request.FilePath; string fileExtension = VirtualPathUtility.GetExtension(filePath);
if (fileExtension.Equals(".gif")) { if (filePath.Contains(beaconUrl)) {
... // Process the beacon parmsapplication.Response.End();
} }
}
Demo using sample data from webscorer.com
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Main Navigation Window
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HTTP activity by URL
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Navigate to URL Detail
Boomerang beacon supportAdd the boomerang.js script to your web page HTML:
Initialize boomerang:
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Web Application Trace Explorer
<script src="javascript\Boomerang\boomerang.js" type="text/javascript"></script><script src="javascript\Boomerang\plug-ins\navtiming.js" type="text/javascript"></script><script src="javascript\Boomerang\plug-ins\rt.js" type="text/javascript"></script
<script lang="javascript"> BOOMR.init({beacon_url: "boomerang.gif"});</script>
Boomerang beacon support
Add the BoomerangBeacon HttpModule from MeasurementWareWebServices.dll to web.config
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Web Application Trace Explorer
<system.webServer> <modules> <add name="MeasurementWareWebServices“ type="MeasurementWareWebServices.BoomerangBeacon"/> </modules> </system.webServer>
BoomerangBeacon classderives from IHttpModuleadds an EventHandler for HttpApplication.BeginRequest
In the BeginRequest event handler,intercepts the boomerang.gif GET Requestsparse the beacon parmsgenerate a MeasurementWareWeb ETW event whose payload includes
Page Load Time measurementsplus, IP Address and Tcp Port (unique session ID) of the Sender for correlation with
other HttpServer and TcpIP events
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Web Application Trace Explorer
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Beacon data summarized by URL
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Navigate to URL Detail
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Initial stage of the work to add Boomerang beacon data to the event collection and the displays is functionally complete
Prototype real-time collector that reports HTTP Response time measurements (by URL) as Windows performance counters is currently available
Contact me if your org is interested in [email protected] my blog at
http://computerperformancebydesign.com for the latest status (until it reaches the Release to github stage)
Web App Trace Explorer: Project Status
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Questions
