Any Recommended Java Profiling Tutorial

Any recommended Java profiling tutorial?

Profiling is a subject having more than one school of thought.

The more popular one is that you proceed by getting measurements. That is, you try to see how long each function takes and/or how many times it is called. Clearly, if a function takes very little time, then speeding it up will gain you little. But if it takes a lot of time, then you have to do detective work to figure out what part of the function is responsible for the time. Do not expect function times to add up to total time, because functions call each other, and the reason function A may take a lot of time is that it calls function B that also takes a lot of time.

This approach can find a lot of problems, but it depends on you being a good detective and being able to think clearly about different kinds of time, like wall-clock time versus CPU time, and self-time versus inclusive time. For example, an application may appear to be slow but the function times may be all reported as near zero. This can be caused by the program being I/O bound. If the I/O is something that you expect, that may be fine, but it may be doing some I/O that you don't know about, and then you are back to detective work.

General expectation with profilers is that if you can fix enough things to get a 10% or 20% speedup, that's pretty good, and I never hear stories of profilers being used repeatedly to get speedups of much more than that.

Another approach is not to measure, but to capture. It is based on the idea that, during a time when the program is taking longer (in wall-clock time) than you would like, you want to know what it is doing, predominantly, and one way to find out is to stop it and ask, or take a snapshot of its state and analyze it to understand completely what it is doing and why it is doing it at that particular point in time. If you do this multiple times and you see something that it is trying to do at multiple times, then that activity is something that you could fruitfully optimize. The difference is that you are not asking how much; you are asking what and why. Here's another explanation. (Notice that the speed of taking such a snapshot doesn't matter, because you're not asking about time, you're asking what the program is doing and why.)

In the case of Java, here is one low-tech but highly effective way to do that, or you can use the "pause" button in Eclipse. Another way is to use a particular type of profiler, one that samples the entire call stack, on wall-clock time (not CPU unless you want to be blind to I/O), when you want it to sample (for example, not when waiting for user input), and summarizes at the level of lines of code, not just at the level of functions, and percent of time, not absolute time. To get percent of time, it should tell you, for each line of code that appears on any sample, the percent of samples containing that line, because if you could make that line go away, you would save that percent. (You should ignore other things it tries to tell you about, like call graphs, recursion, and self-time.) There are very few profilers that meet this specification, but one is RotateRight/Zoom, but I'm not sure if it works with Java, and there may be others.

In some cases it may be difficult to get stack samples when you want them, during the time of actual slowness. Then, since what you are after is percentages, you can do anything to the code that makes it easier to get samples without altering the percentages. One way is to amplify the code by wrapping a temporary loop around it of, say, 100 iterations. Another way is, under a debugger, to set a data-change breakpoint. This will cause the code to be interpreted 10-100 times slower than normal. Another way is to employ an alarm-clock timer to go off during the period of slowness, and use it to grab a sample.

With the capturing technique, if you use it repeatedly to find and perform multiple optimizations, you can expect to reach near-optimal performance. In the case of large software, where bottlenecks are more numerous, this can mean substantial factors. People on Stack Overflow have reported factors from 7x to 60x. Here is a detailed example of 43x.

The capturing technique has trouble with cases where it is hard to figure out why the threads are waiting when they are, such as when waiting for a transaction to complete on another processor. (Measuring has the same problem.) In those cases, I use a laborious method of merging time-stamped logs.

Profiling a Java Spring application

I've done this using Spring AOP.

Sometime I need an information about how much time does it take to execute some methods in my project (Controller's method in example).

In servlet xml I put

<aop:aspectj-autoproxy/>

Also, I need to create the class for aspects:

@Component
@Aspect
public class SystemArchitecture {

    @Pointcut("execution(* org.mywebapp.controller..*.*(..))")
    public void businessController() {
    }
}

And profiler aspect:

@Component
@Aspect
public class TimeExecutionProfiler {

    private static final Logger logger = LoggerFactory.getLogger(TimeExecutionProfiler.class);

    @Around("org.mywebapp.util.aspects.SystemArchitecture.businessController()")
    public Object profile(ProceedingJoinPoint pjp) throws Throwable {
        long start = System.currentTimeMillis();
        logger.info("ServicesProfiler.profile(): Going to call the method: {}", pjp.getSignature().getName());
        Object output = pjp.proceed();
        logger.info("ServicesProfiler.profile(): Method execution completed.");
        long elapsedTime = System.currentTimeMillis() - start;
        logger.info("ServicesProfiler.profile(): Method execution time: " + elapsedTime + " milliseconds.");

        return output;
    }

    @After("org.mywebapp.util.aspects.SystemArchitecture.businessController()")
    public void profileMemory() {
        logger.info("JVM memory in use = {}", (Runtime.getRuntime().totalMemory() - Runtime.getRuntime().freeMemory()));
    }
}

That's all.
When I request a page from my webapp, the information about method executing time and JVM memory usage prints out in my webapp's log file.

Java Profiling Tool for Linux

All these Java profiling tools can be used in Linux:

Yourkit
JProfiler
HPROF (Java 5+)
JRat

How do I analyze which method consumed more time in java,eclipse,junit?

Use jvisualvm. It is bundled in with the JDK nowadays, but a standalone version exists as well, which is more up to date.
Typically, when you start it you can pick which running java process to connect to (this may well be our running unit test). You can specify which qualified class name filters you need to track. Normally, some class instrumentation will ensue, and you will be able to track the processing time allocated to each method (cumulative time as well).

Java application profiling

Take a look at Java Mission Control in conjunction with Flight Recorder. Starting with the release of Oracle JDK 7 Update 40 (7u40), Java Mission Control is bundled with the HotSpot JVM, so it is highly integrated and purports to have small effects on run-time performance. I have only just started looking at it, and I do see some call tree functionality.

Sample Image

Open Source Java Profilers

The VisualVM which comes with jdk6 has a basic profiler inside it.
VisualVM is provided with the jdk, so if you have the jdk6 installed, you likely have it installed as well.

https://visualvm.github.io/

recommendation for a good JSF profiler

If you're using an IDE like Eclipse or Netbeans, then the builtin profiler or the ones which are available as a plugin will in most cases already suffice. It all depends on the features and the level of detail the profiler provides.

Eclipse for Java EE ships with TPTP which can also be installed as a plugin in Eclipse versions lacking the profiler. Just deploy project to server, rightclick server instance and choose Profile on server. You'll be brought to Profiling and logging perspective wherein you can examine the profiler results.

Netbeans has its own profiler which is based on JDK's builtin VisualVM profiler (actually, it's the other way round, the VisualVM was born out of the Netbeans profiler ages ago).

Talking about VisualVM, you can also use it independently if you have the JDK installed. You can use it to profile Tomcat as well. Here's a nice blog article about that.

You can by the way stresstest webapplications using JMeter.

How to write a profiler?

I would look at those open-source projects first:

Eclipse TPTP (http://www.eclipse.org/tptp/)
VisualVM (https://visualvm.dev.java.net/)

Then I would look at JVMTI (not JVMPI)

http://java.sun.com/developer/technicalArticles/Programming/jvmti/

Any Recommended Java Profiling Tutorial