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Everything about Web and Network Monitoring

Website Performance: Synchronicity Wrapup

Website Performance: Taxonomy of Tips in­tro­duced a clas­si­fi­ca­tion scheme to help us or­ga­nize the many per­form­ance tips found on the In­ter­net.  To­day’s ar­ti­cle de­scribes a few tips that re­late to the synchronicitycategory.

Set Priority Levels

Some languages allow pro­gram­m­ers to set CPU pri­o­ri­ty levels.  Down­load­ing Java­Script told us to down­load maybe-needed-later scripts af­ter ex­e­cut­ing needed-soon scripts.  How­e­ver, if we could set CPU pri­o­ri­ty lev­els, we can pre­load scripts that may be need­ed on the next page in par­al­lel with scripts that are need­ed on the cur­rent page, but at a low­er pri­o­ri­ty.  This achieves asyn­chro­ni­za­tion with­out de­lay­ing the scripts that are need­ed first.

Sett­ing pri­o­ri­ty lev­els in other ar­e­as of our code is a bit of an art form, but suc­cess­ful im­ple­men­ta­tion of pri­o­ri­tized mul­ti­pro­cess­ing can pro­vide per­for­m­ance be­ne­fits.

Fork Processing Within Scripts and Tools

Some pro­gramm­ing lan­gua­ges let us fork (cre­ate asyn­chron­ous back­ground tasks for) our code.  For ex­am­ple, we can pop­u­late a Mon­i­tis mon­i­tor in an asyn­chro­nous back­ground task.  As long as the system is not near ca­pa­ci­ty, asyn­chro­n­ous pro­gram­m­ing may de­liv­er bet­ter per­for­m­ance.  This tip can be applied to server-side and client-side processing.

A few years ago, Rob Howard said:

It turned out that the built-in System.Web.Mail func­tion­al­i­ty would con­nect to an SMTP ser­v­er and send the e-mails ser­i­al­ly. …  Ideal­ly, we want­ed to batch this work to­geth­er and in­dex 25 posts at a time or send all the e-mails every five mi­n­utes. … The Timer class … will in­voke the spe­ci­fied call­back … at a con­fig­ur­able in­ter­val.  You can do work such as in­dex­ing or send­ing e-mail in this background process too.

Rob goes on to explain a coup­le of timer-related gotchas, but this ap­proach is sound.  Send­ing e-mail can be batched and off­load­ed on­to an asyn­chro­n­ous, low-priority background process.

Split Components Across Multiple Domains

Browsers limit how many re­sour­ces can be down­load­ed in paral­lel from each do­main.  If our re­sour­ces are split across two or more do­mains (or IP ad­dres­ses), we can in­crease the num­ber of si­mul­ta­ne­ous down­loads.  Tenni Theurer and Steve Souders de­mon­strat­ed that there is a li­mit to the ef­fect­ive­ness of this ap­proach, though.  As we in­crease the num­ber of do­mains, the per­for­m­ance can ac­tu­al­ly start to de­crease.

If we do not have mul­ti­ple do­mains and IP ad­dres­s­es avail­able to us, con­tent de­li­very net­works can be used for this pur­pose.

Flush the Buffer

The PHP flush() func­tion can be used to send all the cur­rently-buffered HTML to the brow­ser, which al­lows us to asyn­chro­n­ize page ren­der­ing and server-side pro­cess­ing.  There are se­ver­al opin­ions on when to do this, but it seems to come down to flush­ing af­ter every outer </div> tag.

This tip is not as sim­ple as it sounds.  Check the ma­n­ual to learn about the li­mi­t­a­tions and problems.  The best advice I can of­fer is to flush fre­quent­ly, but don’t be sur­prised if it pro­vides no be­ne­fit.

Avoid AlphaImageLoader

According to Stoyan Stefanov and others, trans­paren­cies in .png files may not dis­play cor­rect­ly in some ver­sions of In­ter­net Ex­plor­er.  Some pro­gram­m­ers use Mi­cro­soft’s Alpha­Image­Loader fil­ter to re­solve the prob­lem, but in so do­ing, they cre­ate anoth­er prob­lem – the brow­ser free­z­es while the im­age is down­load­ing.  It doesn’t mere­ly block on­load; it free­z­es the en­tire brow­ser.  The user can’t even type in a new URL.

AlphaImageLoader is not re­com­mend­ed be­cause it in­ter­feres with asyn­chro­ni­za­tion.  Use grace­fully-degrad­ing PNG8 rather than true-colour PNG.

As more people use more-recent brow­sers, this prob­lem will go away and we will be able to use true-colour PNG’s with trans­paren­cy.  For the most part, this prob­lem is no long­er a con­cern be­cause on­ly users with very old brow­sers are af­fect­ed by it to­day.  Le­g­a­cy code should be changed to re­move Alpha­Image­Loader if old­er brow­sers are no longer a concern.

Downloading Components

Downloading JavaScript ex­plained all the ins and outs of down­load­ing and ex­e­cut­ing Java­Script asyn­chro­nous­ly with­out block­ing down­load­ing, ex­e­cu­tion, pars­ing, and on­load.  Si­mi­lar con­cepts ap­ply to images, style sheets, ob­jects, and other components.

Other components can be load­ed asyn­chro­nous­ly af­ter on­load in the same way that Java­Script can be load­ed asyn­chro­nous­ly af­ter on­load.  We can se­pa­rate all com­po­nents in­to the same three ca­te­go­r­ies (needed-now, needed-soon, and maybe-needed-later) and down­load each ca­te­go­ry using the ap­proach de­scribed in Downloading JavaScript.

Note that images and other com­po­nents below-the-fold (i.e., down the page so far that the user doesn’t see them without scroll­ing) are in the needed-soon ca­te­go­ry, not the needed-now category.

Note, too, that CSS used for ini­tial for­mat­t­ing is in the needed-now ca­te­go­ry, so it should be in­clud­ed in­side the head of the do­c­u­ment.  If its ex­pi­ry date is short­ly af­ter the HTML’s, in­line it rath­er than load­ing it ex­ter­nal­ly.

The Paid Monitor page-load test­ing toolpro­vides a wa­ter­fall chart to let us see what com­po­n­ents are be­ing load­ed, in what or­der, and how long each one takes.  We can in­stant­ly see how well our per­formance-improve­ment ef­forts are pay­ing off.  It’s free and sim­ple to use (just type in the URL).  Con­ti­n­u­al mo­n­i­tor­ing on a trans­action-by-trans­action basis is avail­ab­le at Mo­ni­tis Transaction Monitoring.

Grow an IIS Web Garden

As Mikayel Vardanyan coun­selled in Top 8 Application-Based IIS Ser­ver Per­for­m­ance Tips, grow­ing an IIS web gar­den im­proves per­for­m­ance by creat­ing asyn­chro­nous web­page con­nec­tions.  When this is done right, it im­proves over­all server performance.


Best Practices for Speeding Up Your Web Site by Yahoo’s Exceptional Performance Team.  Published by Yahoo at  Accessed 2012.01.13.

Custom Monitors in Paid Monitor with Python by Hovhannes Avoyan.  Published 2011.07.07 by Paid Monitor at  Accessed 2012.01.13.

Even Faster Web Sites: Performance Best Practices for Web Developers (ISBN 978-0-596-52230-8) by Steve Souders.  Published June 2009 by O’Reilly Media.

High Performance Web Sites – 14 Rules for Faster-Loading Web Sites by Steve Souders.  Published by Steve Souders at  Accessed 2012.01.13.

Paid Monitor Free Page Load Testing Tool.  Published by Paid Monitor at  Accessed 2012.01.13.

Paid Monitor Transaction Monitoring.  Published by Paid Monitor at  Accessed 2012.01.13.

The Not So Good Web Performance Tips by José Manuel Perez.  Published 2010.12.28 by José Manuel Perez at  Accessed 2012.01.13.  José shows that two tips do not work as expected – putting scripts at the bottom of the page and flushing inside a <div> tag.

Performance on the Yahoo! Homepage by Nicholas C. Zakas.  Published by at  Accessed 2012.01.13.  This slideshow shows how to dynamically load JavaScript without blocking rendering.  It also discusses where to flush and advises us to keep JSON data small.

Performance Research, Part 4: Maximizing Parallel Downloads in the Carpool Lane by Tenni Theurer and Steve Souders.  Published 2007.04.11 by Yahoo at  Accessed 2012.01.13.

Ten Tips for Writing High-Performance Web Applications by Rob Howard.  Published January 2005 by Microsoft at  Accessed 2012.01.13.

Top 8 Application-Based IIS Server Performance Tips by Mikayel Vardanyan.  Published 2011.06.13 by Paid Monitor at  Accessed 2012.01.13.

Web Performance Best Practices.  Published by Google at  Accessed 2012.01.13.

Website Performance: Taxonomy of Tips by Warren Gaebel.  Published 2011.12.29 by Paid Monitor at  Accessed 2012.01.13.

Try Paid Monitor For Free.  A 15-day free trial.  Your opportunity to see how easy it is to use the Paid Monitor cloud-based monitoring system.  Credit card not required.  Accessed 2012.01.13.

The Paid Monitor Exchange at GitHub.  This is the official repository for scripts, plugins, and SDKs that make it a breeze to use the Paid Monitor system to its full potential.  Accessed 2012.01.13.

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About Warren Gaebel

Warren wrote his first computer program in 1970 (yes, it was Fortran).  He earned his Bachelor of Arts degree from the University of Waterloo and his Bachelor of Computer Science degree at the University of Windsor.  After a few years at IBM, he worked on a Master of Mathematics (Computer Science) degree at the University of Waterloo.  He decided to stay home to take care of his newborn son rather than complete that degree.  That decision cost him his career, but he would gladly make the same decision again. Warren is now retired, but he finds it hard to do nothing, so he writes web performance articles for the Monitor.Us blog.  Life is good!