Eclipse Memory analyzer http://www.eclipse.org/mat/

 - Support for multiple JVMs
 - Help with identifying sources for memory leaks
(see http://www.sdn.sap.com/irj/scn/weblogs?blog=/pub/wlg/6856)
 - Open source and actively developed by major vendors (SAP and IBM)
 - Part of Galileo release of Eclipse



Java VisualVM, [jvisualvm](http://java.sun.com/javase/6/docs/technotes/tools/share/jvisualvm.html), included with the JDK. A pathologic Swing program is examined [here][1].


  [1]: https://stackoverflow.com/q/6309407/230513

**YourKit** : http://www.yourkit.com/

**Pros:**

 * The interface is clean and it&#39;s fast
 * It opened a large 5-gig heap dump where jProfiler grined to a halt. And it only needed 1-2 gigs of JVM ram to do so.

**Cons:**
Of course... it&#39;s not free :(

BHeapSampler http://dr-brenschede.de/bheapsampler/

 - generates a class-level heap-graph as a really intuitive display of the dominant memory structures
 - can process really large heap dumps
 - command-line tool, usable on server side without transfering the dump to the developer&#39;s desk


How can I change the password for `root` user of MySQL to `null` -- meaning no password or `&#39;&#39;` -- from the MySQL command line client?

How to set root password to null

How can I tell if a given directory is part of a git respository?

(The following is in python, but bash or something would be fine.)

    os.path.isdir(&#39;.svn&#39;)

will tell you if the current directory is controlled by Subversion. Mercurial and Git just have a .hg/.git at the top of the repository, so for `hg` I can use

    os.system(&#39;hg -q stat 2&gt; /dev/null &gt; /dev/null&#39;) == 0)

but `git status` returns a nonzero (error) exit status if nothing&#39;s changed.

Is iterating up the path looking for `.git` myself the best I can do?

Determine if directory is under git control

List your favorite heap analysis tools (e.g. jprofiler, jmap, ...).
Let&#39;s keep it one tool per answer, with a short list of pros and cons for each tool.

Recommendations for a heap analysis tool for Java?

<p>List your favorite heap analysis tools (e.g. jprofiler, jmap, ...).
Let's keep it one tool per answer, with a short list of pros and cons for each tool.</p>


I am thinking this may not be possible in Java because annotation and its parameters are resolved at compile time. I have an interface as follows,

    public interface FieldValues {
       String[] FIELD1 = new String[]{&quot;value1&quot;, &quot;value2&quot;};
    }

and another class as,

    @SomeAnnotation(locations = {&quot;value1&quot;, &quot;value2&quot;})
    public class MyClass {
       ....
    }

I mark many classes with the annotation and I would like to know if I can avoid specifying the strings in every annotation I would instead prefer to use

    @SomeAnnotation(locations = FieldValues.FIELD1)
    public class MyClass {
       ....
    }

However this gives compilation errors like annotation value should be an array initializer etc. Does someone know how I can use a String constant or String[] constant to supply value to an annotation?

How to supply value to an annotation from a Constant java

Is there a specific rule on how Overriding `equals()` &amp; `hashCode()` in **sub classes** considering **super fields** ?? knowing that there is many parameters : super fields are private/public , with/without getter ...

For instance, Netbeans generated equals() &amp; hashCode() will not consider the super fields ... and

        new HomoSapiens(&quot;M&quot;, &quot;80&quot;, &quot;1.80&quot;, &quot;Cammeron&quot;, &quot;VeryHot&quot;).equals(
        new HomoSapiens(&quot;F&quot;, &quot;50&quot;, &quot;1.50&quot;, &quot;Cammeron&quot;, &quot;VeryHot&quot;))

will return true :(

    public class Hominidae {
        
        public String  gender;
        public String  weight;
        public String  height;
    
        public Hominidae(String gender, String weight, String height) {
            this.gender = gender;
            this.weight = weight;
            this.height = height;
        }
        ... 
    }
    
    public class HomoSapiens extends Hominidae {
        public String name;
        public String faceBookNickname;
    
        public HomoSapiens(String gender, String weight, String height, 
                           String name, String facebookId) {
            super(gender, weight, height);
            this.name = name;
            this.faceBookNickname = facebookId;
        }
        ...  
    }

If you want to see the Netbeans generated equals() &amp; hashCode() :

    public class Hominidae {
        
        ...
        
        @Override
        public boolean equals(Object obj) {
            if (obj == null) {
                return false;
            }
            if (getClass() != obj.getClass()) {
                return false;
            }
            final Hominidae other = (Hominidae) obj;
            if ((this.gender == null) ? (other.gender != null) : !this.gender.equals(other.gender)) {
                return false;
            }
            if ((this.weight == null) ? (other.weight != null) : !this.weight.equals(other.weight)) {
                return false;
            }
            if ((this.height == null) ? (other.height != null) : !this.height.equals(other.height)) {
                return false;
            }
            return true;
        }

        @Override
        public int hashCode() {
            int hash = 5;
            hash = 37 * hash + (this.gender != null ? this.gender.hashCode() : 0);
            hash = 37 * hash + (this.weight != null ? this.weight.hashCode() : 0);
            hash = 37 * hash + (this.height != null ? this.height.hashCode() : 0);
            return hash;
        }

    }


    public class HomoSapiens extends Hominidae {
        
        ...
        
        @Override
        public boolean equals(Object obj) {
            if (obj == null) {
                return false;
            }
            if (getClass() != obj.getClass()) {
                return false;
            }
            final HomoSapiens other = (HomoSapiens) obj;
            if ((this.name == null) ? (other.name != null) : !this.name.equals(other.name)) {
                return false;
            }
            if ((this.faceBookNickname == null) ? (other.faceBookNickname != null) : !this.faceBookNickname.equals(other.faceBookNickname)) {
                return false;
            }
            return true;
        }

        @Override
        public int hashCode() {
            int hash = 7;
            hash = 89 * hash + (this.name != null ? this.name.hashCode() : 0);
            hash = 89 * hash + (this.faceBookNickname != null ? this.faceBookNickname.hashCode() : 0);
            return hash;
        }
    }

Overriding equals() &amp; hashCode() in sub classes ... considering super fields

How do I get a [Spring][1] 3.0 controller to trigger a 404?

I have a controller with `@RequestMapping(value = &quot;/**&quot;, method = RequestMethod.GET)` and for some [URLs][2] accessing the controller, I want the container to come up with a 404.

  [1]: http://en.wikipedia.org/wiki/Spring_Framework
  [2]: http://en.wikipedia.org/wiki/Uniform_Resource_Locator


Trigger 404 in Spring-MVC controller?

Currently in an Android application that I&#39;m developing I&#39;m looping through the pixels of an image to blur it.  This takes about 30 seconds on a 640x480 image.  

While browsing apps in the Android Market I came across one that includes a blur feature and their blur is very fast (like 5 seconds) so they must be using a different method of blurring.

Anyone know a faster way other than looping through the pixels?

Fast Bitmap Blur For Android SDK

From when I learned that the class `java.lang.String` is declared as final in Java, I was wondering why that is. I didn&#39;t find any answer back then, but this post: [How to create a replica of String class in Java?][1] reminded me of my query. 

Sure, String provides all the functionality I ever needed, and I never thought of any operation that would require an extension of class String, but still you&#39;ll never know what someone might need!

So, does anyone know what the intent of the designers was when they decided to make it final? 


  [1]: https://stackoverflow.com/questions/2068570/how-to-create-a-replica-of-string-class-in-java


Why is the String class declared final in Java?

I used a variable with a lot of data in it, say `String data`.
I wanted to use a small part of this string in the following way:
 
    this.smallpart = data.substring(12,18);

After some hours of debugging (with a memory visualizer) I found out that the objects field `smallpart` remembered all the data from `data`, although it only contained the substring.

When I changed the code into:

    this.smallpart = data.substring(12,18)+&quot;&quot;; 

..the problem was solved! Now my application uses very little memory now! 

How is that possible? Can anyone explain this? I think this.smallpart kept referencing towards data, but why? 

**UPDATE:**
How can I clear the big String then? Will data = new String(data.substring(0,100)) do the thing?

Why does appending &quot;&quot; to a String save memory?

I have just found out that my script gives me a fatal error:

    Fatal error: Allowed memory size of 268435456 bytes exhausted (tried to allocate 440 bytes) in C:\process_txt.php on line 109

That line is this:

    $lines = count(file($path)) - 1;

So I think it is having difficulty loading the file into memeory and counting the number of lines, is there a more efficient way I can do this without having memory issues?

The text files that I need to count the number of lines for range from 2MB to 500MB. Maybe a Gig sometimes.

Thanks all for any help.

Efficiently counting the number of lines of a text file. (200mb+)

Is there a function in PHP (or a PHP extension) to find out how much memory a given variable uses? `sizeof` just tells me the number of elements/properties.

`memory_get_usage` helps in that it gives me the memory size used by the *whole* script. Is there a way to do this for a single variable?

Note that this is on a development machine, so loading extensions or debug tools is feasible.

How to determine the memory footprint (size) of a variable?

How can I find the memory used on my Android application, programmatically?

I hope there is a way to do it. Plus, how do I get the free memory of the phone too?


How do I discover memory usage of my application in Android?

I sometimes write Python programs which are very difficult to determine how much memory it will use before execution. As such, I sometimes invoke a Python program that tries to allocate massive amounts of RAM causing the kernel to heavily swap and degrade the performance of other running processes.

Because of this, I wish to restrict how much memory a Python heap can grow. When the limit is reached, the program can simply crash. What&#39;s the best way to do this? 

If it matters, much code is written in Cython, so it should take into account memory allocated there. I am not married to a pure Python solution (it does not need to be portable), so anything that works on Linux is fine.


How to limit the heap size?

XDebug offers the configuration directive `xdebug.profiler_enable_trigger` that allows to activate profiling by passing the GET or POST parameter &quot;XDEBUG_PROFILE&quot; when calling a script via HTTP. This is handy if you don&#39;t want profiling for ALL of your scripts but only for a few special cases without always changing your PHP configuration.

Is there a way to achieve the same behavior for command line PHP programs? I tried to pass the `XDEBUG_PROFILE` as a command line argument but it didn&#39;t work.

In general, profiling command line PHP works well, but I&#39;d like to have the same per-call-flexibility as with a browser and HTTP server.


How to trigger XDebug profiler for a command line PHP script?

My django application has become painfully slow on the production. Probably it is due to some complex or unindexed queries. 

Is there any django-ish way to profile my application?

Profiling Django

I am compiling an IPhone application via command line (so no XCode options involved) and I am unable to get my symbol names to show when profiling with Instruments. I have tried several flags such as -gdawrf-2 and -g without any success. I have also tried using dsymutils to generate a .dSYM file but i have no clue how I&#39;m supposed to use it so that failed aswell.

Any help will be greatly appreciated!

Missing symbol names when profiling IPhone application with Instruments

I&#39;m trying to run the performance wizard on an ASP.Net website.  However, whenever I try to start it I get the following error. 

&quot;The website contains unexpected information or you do not have permission to access the metabase. You must be a member of the Administrators group on the local computer to access the IIS matabase.  Therefore, you cannot create or open a local IIS website.  If you have Read, Write, and Modify Permissions for the folder where the files are located, you can create a file system website that points to the folder in order to proceed&quot;

I am an Administrator on my machine.  Tried googling but came up with nothing.  Anyone run it before and know how to deal with it?

Metabase error when trying to use Visual Studios Profiler on an ASP.Net site

As far is I know, there are a number of ways of selecting child elements in **jQuery**.

    //Store parent in a variable  
    var $parent = $(&quot;#parent&quot;);

**Method 1** *(by using a scope)*

    $(&quot;.child&quot;, $parent).show();

**Method 2** *(the find() method)*

    $parent.find(&quot;.child&quot;).show();

**Method 3** *(For immediate children only)*

    $parent.children(&quot;.child&quot;).show();

**Method 4** *(via CSS selector)* - suggested by @spinon

    $(&quot;#parent &gt; .child&quot;).show();

**Method 5** *(identical to **Method 2**)* - according to @Kai

    $(&quot;#parent .child&quot;).show();

I&#39;m not familiar with profiling to be able to investigate this on my own, so I would love to see what you have to say.


P.S. I understand this is a possible duplicate of [this question][1] but it doesn&#39;t cover all methods.



  [1]: https://stackoverflow.com/questions/648004/what-is-fastest-children-or-find-in-jquery

What is the fastest method for selecting descendant elements in jQuery?

I&#39;m confused with Heap,Young,Tenured and Perm generation. 

Could anyone please explain?

Young , Tenured and Perm generation

I have an array declaration like this:

    int a[];

Here `a` is an array of primitive `int` type. Where is this array stored? Is it stored on heap or stack? This is a primitve type `int`, all primitive types are not stored on heap.

Is a Java array of primitives stored in stack or heap?

I&#39;m trying to understand What the concepts of &lt;b&gt;young&lt;/b&gt;, &lt;b&gt;old&lt;/b&gt; and &lt;b&gt;permanent generations&lt;/b&gt; are in the Java heap terminology, and more specifically the interactions between the three generations.

My questions are:

* What is the young generation?
* What is the old generation?
* What is the permanent generation?
* How does the three generations interact/relate to each other?


Java heap terminology: young, old and permanent generations?

How do you programmatically detect the application heap size available to an Android app?

I heard there&#39;s a function that does this in later versions of the SDK. In any case, I&#39;m looking for solution that works for 1.5 and upwards.

Detect application heap size in Android

We have an open beta of an app which occasionally causes the heapspace to overflow. The JVM reacts by going on a permanent vacation. 

To analyze this I would like to peek into the memory at the point where it failed. Java does not want me to do this. The process is still in memory but it doesn&#39;t seem to be recognized as a java process.

The server in question is a debian Lenny server, Java 6u14

    /opt/jdk/bin# ./jmap -F -dump:format=b,file=/tmp/apidump.hprof 11175
    Attaching to process ID 11175, please wait...
    sun.jvm.hotspot.debugger.NoSuchSymbolException: Could not find symbol &quot;gHotSpotVMTypeEntryTypeNameOffset&quot; in any of the known library names (libjvm.so, libjvm_g.so, gamma_g)
    at sun.jvm.hotspot.HotSpotTypeDataBase.lookupInProcess(HotSpotTypeDataBase.java:390)
    at sun.jvm.hotspot.HotSpotTypeDataBase.getLongValueFromProcess(HotSpotTypeDataBase.java:371)
    at sun.jvm.hotspot.HotSpotTypeDataBase.readVMTypes(HotSpotTypeDataBase.java:102)
    at sun.jvm.hotspot.HotSpotTypeDataBase.&lt;init&gt;(HotSpotTypeDataBase.java:85)
    at sun.jvm.hotspot.bugspot.BugSpotAgent.setupVM(BugSpotAgent.java:568)
    at sun.jvm.hotspot.bugspot.BugSpotAgent.go(BugSpotAgent.java:494)
    at sun.jvm.hotspot.bugspot.BugSpotAgent.attach(BugSpotAgent.java:332)
    at sun.jvm.hotspot.tools.Tool.start(Tool.java:163)
    at sun.jvm.hotspot.tools.HeapDumper.main(HeapDumper.java:77)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at sun.tools.jmap.JMap.runTool(JMap.java:179)
    at sun.tools.jmap.JMap.main(JMap.java:110)
    Debugger attached successfully.
    sun.jvm.hotspot.tools.HeapDumper requires a java VM process/core!


Content Type	Original Author	Original Content on Stackoverflow
Question	ripper234	View Question on Stackoverflow
Solution 1 - Java	dparnas	View Answer on Stackoverflow
Solution 2 - Java	trashgod	View Answer on Stackoverflow
Solution 3 - Java	nanda	View Answer on Stackoverflow
Solution 4 - Java	Arndt	View Answer on Stackoverflow

Recommendations for a heap analysis tool for Java?

Java Problem Overview

Java Solutions

Solution 1 - Java

Solution 2 - Java

Solution 3 - Java

Solution 4 - Java

Determine if directory is under git control

How to set root password to null

Attributions