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Walmart uses a java + database architecture to serve over 100 million pages per day. Another example of Java's ability to scale you might think. But do we know enough about the details of the site to make that claim?

What I do know (see our news items listed below) is enough to say some interesting things. 100 million pages a day sounds like a lot. Moved over to a per-second rate it amounts to over one thousand pages delivered each second. Spread over 100 machines, it amounts to 10 pages delivered per second per machine. Hmm, maybe that doesn't sound quite so impressive?

But it is. You see, you have to factor in two important issues. Firstly, serving static pages compared to serving session specific dynamic pages are two very different problems. To get good performance for a site with that level of load you have to have architected it to handle each type of page in the most appropriate way, otherwise your site will get bogged down by overheads in one or the other type of page. And secondly, you cannot just take an arbitrary session oriented application, distribute over a cluster and get instant scalability. Again, you have to architect the application to manage horizontal scalability (i.e. over a cluster), otherwise the application quickly gets bogged down in one of many potential limitations to scalability, like cache synchronization, session distribution, etc.

A note from this newsletter's sponsor

So those figures are enough to tell us two things: that the Walmart website is sufficiently well architected that it correctly scales horizontally, handling different page types appropriately; and that Java was not a handicap in making that happen - in fact I expect java was actually a help in making that happen, but I don't have enough information to say that, so I'll make that weaker claim.

All that should tell you two things: getting the architecture right is important; and there is no reason not to use Java - Java is fast enough and can scale well. And that is something I have been saying for a long time, but it never hurts to repeat it.

Now on with the rest of this month's newsletter - our usual raft of articles, news and tools, and new performance tips extracted in concise form.

News

Java performance tuning related news.

• Suggestion for improving the ability of JVMs to report object counts in a low overhead way.
• Walmart.com serves 7 million sessions/106million page views per day using Apache/Tomcat running on a loosely coupled cluster of over one hundred servers. [Note, the page has subsequently disappeared, so if it doesn't come back you'll just have to believe our summary].
• DTrace to work with Java
• Collections benchmark results
• Note point 5: 5.0 Java VM now supports class literals in the constant pool. This means that "Foo.class" no longer forces a class load (as no need to get the class object since the literal is accessed from the class literal pool).

A note from this newsletter's sponsor

Tools

• Indicative Application Performance Management (APM) Suite provides end-to-end monitoring of Java applications
• ActiveCluster framework for writing cluster-based applications, monitoring the available nodes in a cluster and communicating with them.
• Mercury monitoring and tuning for J2EE
• ConcurrentTesting tool for finding concurrency problems in multi-threaded applications
• Java PathFinder (JPF) is a system to verify executable Java bytecode programs. JPF is especially suitable to find hard-to-test concurrency defects in multithreaded programs.
• Stripper is a tool that lets you strip down class file attributes selectively from a command line or from Ant to make class files smaller.

Recent Articles

• Synchronizers & Garbage Collection Options (John Zukowski/Sun)
• Queues and Delayed Processing (John Zukowski/Sun)
• Java Doctor Chapter 5: Profiling (Ali Syed, Jamiel Sheikh/Manning)
• Java Doctor Chapter 9: Action and Pitfall Tips (Ali Syed, Jamiel Sheikh/Manning)

Jack Shirazi

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