Default values for JDK 1.6.0_29 on Windows 7/32-bit:

    -Xmx256m
    -XX:MaxPermSize=64m

Also value of these option can be printed by following command:

    java -XX:+UnlockExperimentalVMOptions -XX:+UnlockDiagnosticVMOptions -XX:+PrintFlagsFinal -version 2&gt;&amp;1

Then look for MaxHeapSize and MaxPermSize keys and see default values.

    uintx InitialHeapSize                          := 199947456       {product}
    uintx MaxHeapSize                              := 268435456       {product}           
    uintx MaxPermSize                               = 67108864        {pd product}        


[Here][1] is the Ultimate HotSpot VM Options Cheat Sheet with defaults and descriptions for last 5 versions of JDK (7, 8, 9, 10 &amp; 11).


  [1]: https://chriswhocodes.com/hotspot_options_jdk11.html

Hope this question wasn&#39;t asked before. Does anyone know the character limit for domain names?
For example if I write this:

    CREATE DOMAIN d_complement_activite_etablissement AS character varying

it will create a domain with the name:

    d_complement_activite_etabliss

(Yeah, I know how to count, but I want some more info on the subject).

Is there a command that can change this maximum length? Is this length the same for other names (columns, tables etc)?

Maximum characters in labels (table names, columns etc)

I have made an application for my client by keeping target iOS as 4.  
But since the application still not submitted to Apple store, my client is planning to upgrade it for iOS 5.0.  

For this I read the [guideline from Apple][1] and found that &quot;Only user-generated data or that cannot otherwise be recreated by your application, should be stored in the &lt;Application_Home&gt;/Documents directory and rest should be stored to &lt;Application_Home&gt;/Library/Caches directory&quot; 

In my application, I am using server model of in-app purchase for non-consumable product. For this I am storing all my downloaded data (which are basically books or magazines) to Documents directory. The Database is also present in the same directory which contains the details about the downloaded products.  

My question is,  
1. Should I have to change my code to store the downloaded data to Library/Caches directory instead of to the Documents directory?  
2. Where should my database file be placed (to Documents or Caches)?  

If I put it products in the Caches then I have to change the logic of retrieval also, since it is considered that if record is present in database, there is no need change the existence of the file and it directly opens it when user clicks on the magazine.  

Kindly guide me on this issue.  
Thanks in advance.

**UPDATED:**  
I am updating this for those who are still not sure about this problem.  
Using the guideline of accepted answer, I have implemented this in 2 of my applications and submitted them to Apple Store. Both were approved in review.  
This may promote that the solution suggested in the accepted answer is correct.  

  [1]: https://developer.apple.com/icloud/documentation/data-storage/

iOS 5 does not allow to store downloaded data in Documents directory?

What are the default values for the following options in Java 6 on a *non-server-class machine*?

 - -Xmx
 - -XX:MaxPermSize

Oracle&#39;s [documentation][1] states that:

&gt; On server-class machines running the server VM, the garbage collector (GC) has changed from the previous serial collector (-XX:+UseSerialGC) to a parallel collector (-XX:+UseParallelGC).

and

&gt; On server-class machines running either VM (client or server) with the parallel garbage collector (-XX:+UseParallelGC) the initial heap size and maximum heap size have changed

The page doesn&#39;t describe the defaults for non-server-class machines, only that, for example, the initial heap size is &quot;a reasonable minimum&quot;. Looking at [the &#39;man page&#39;][2] for the `java` command there is the following against `-Xms`:

&gt; The default value is chosen at runtime based on system configuration 


  [1]: http://docs.oracle.com/javase/6/docs/technotes/guides/vm/gc-ergonomics.html
  [2]: http://docs.oracle.com/javase/6/docs/technotes/tools/windows/java.html

Default values for Xmx, Xms, MaxPermSize on non-server-class machines

What are the default values for the following options in Java 6 on a non-server-class machine?
<ul>
<li>-Xmx</li>
<li>-XX:MaxPermSize</li>
</ul>
Oracle's <a href="http://docs.oracle.com/javase/6/docs/technotes/guides/vm/gc-ergonomics.html" target="_blank" rel="noopener noreferrer">documentation</a> states that:
> On server-class machines running the server VM, the garbage collector (GC) has changed from the previous serial collector (-XX:+UseSerialGC) to a parallel collector (-XX:+UseParallelGC).
and
> On server-class machines running either VM (client or server) with the parallel garbage collector (-XX:+UseParallelGC) the initial heap size and maximum heap size have changed
The page doesn't describe the defaults for non-server-class machines, only that, for example, the initial heap size is "a reasonable minimum". Looking at <a href="http://docs.oracle.com/javase/6/docs/technotes/tools/windows/java.html" target="_blank" rel="noopener noreferrer">the 'man page'</a> for the <code>java</code> command there is the following against <code>-Xms</code>:
> The default value is chosen at runtime based on system configuration

We&#39;ve run into a **Java.lang.OutOfMemoryError: PermGen space** error and looking at the tomcat JVM params, other than the `-Xms` and `-Xmx` params we also specify `-XX:MaxPermSize=128m`. After a bit of profiling I can see occasionally garbage collection happening on the PermGen space saving it from running full.

My question is: other than increasing the `-XX:MaxPermSize` what would be the difference if I specify as well `-XX:PermSize`? I know the total memory then would be **Xmx+maxPermSize** but is there any other reason why `-XX:PermSize` should **not** be there when `-XX:MaxPermSize` is specified?

Please do share if you have real-world experience dealing with these JVM parameters.

ps. The JVM is HotSpot 64bit Server VM build 16.2-b04



-XX:MaxPermSize with or without -XX:PermSize

For example:
    
    class A {
        static int i=0;
        static int j;

       static void method() {
           // static k=0; can&#39;t use static for local variables only final is permitted
           // static int L;
        }
    }

Where will these variables be stored in Java, in heap or in stack memory? How are they stored?

Where are static methods and static variables stored in Java?

I am unable to understand the following text... Does it mean that `&lt;clinit&gt;` is for empty constructors? Why is important to have two different versions?

https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-2.html

&gt;     2.9. Special Methods
&gt; 
&gt; At the level of the Java virtual machine, every constructor (&#167;2.12) appears as an instance initialization method that has the
&gt; special name `&lt;init&gt;`. This name is supplied by a compiler. Because the
&gt; name `&lt;init&gt;` is not a valid identifier, it cannot be used directly in a
&gt; program written in the Java programming language. Instance
&gt; initialization methods may be invoked only within the Java virtual
&gt; machine by the invokespecial instruction, and they may be invoked only
&gt; on uninitialized class instances. An instance initialization method
&gt; takes on the access permissions (&#167;2.7.4) of the constructor from which
&gt; it was derived.
&gt;     
&gt; A class or interface has at most one class or interface initialization method and is initialized (&#167;2.17.4) by invoking that
&gt; method. The initialization method of a class or interface is static
&gt; and takes no arguments. It has the special name `&lt;clinit&gt;`. This name is
&gt; supplied by a compiler. Because the name `&lt;clinit&gt;` is not a valid
&gt; identifier, it cannot be used directly in a program written in the
&gt; Java programming language. Class and interface initialization methods
&gt; are invoked implicitly by the Java virtual machine; they are never
&gt; invoked directly from any Java virtual machine inw2struction, but are
&gt; invoked only indirectly as part of the class initialization process.

Java: What is the difference between &lt;init&gt; and &lt;clinit&gt;?

I am studying new features of JDK 1.7 and I just can&#39;t get it what MethodHandle is designed for? I understand (direct) invocation of the static method (and use of Core Reflection API that is straightforward in this case). I understand also (direct) invocation of the virtual method (non-static, non-final) (and use of Core Reflection API that requires going through Class&#39;s hierarchy `obj.getClass().getSuperclass()`). Invocation of non-virtual method can be treated as special case of the former one.

Yes, I aware that there is an issue with overloading. If you want to invoke method you have to supply the exact signature. You can&#39;t check for overloaded method in easy way.

But, what is MethodHandle about? Reflection API allows you to &quot;look on&quot; the object internals without any pre-assumption (like implemented the interface). You can inspect the object for some purpose. But what is MethodHandle is designed too? Why and when should I use it?

**UPDATE:** I am reading now this http://blog.headius.com/2008/09/first-taste-of-invokedynamic.html article. According to it, the main goal is to simplify life for scripting languages that runs atop of JVM, and not for Java Language itself.

**UPDATE-2:** I finish to read the link above, some quotation from there:

&gt;The JVM is going to be the best VM for building dynamic languages, because it already is a dynamic language VM. And InvokeDynamic, by promoting dynamic languages to first-class JVM citizens, will prove it.
&gt;
&gt;Using reflection to invoke methods works great...except for a few problems. Method objects must be retrieved from a specific type, and can&#39;t be created in a general way.&lt;...&gt; 
&gt;
&gt;...reflected invocation is a lot slower than direct invocation. Over the years, the JVM has gotten really good at making reflected invocation fast. Modern JVMs actually generate a bunch of code behind the scenes to avoid a much of the overhead old JVMs dealt with. But the simple truth is that reflected access through any number of layers will always be slower than a direct call, partially because the completely generified &quot;invoke&quot; method must check and re-check receiver type, argument types, visibility, and other details, but also because arguments must all be objects (so primitives get object-boxed) and must be provided as an array to cover all possible arities (so arguments get array-boxed).
&gt;
&gt;The performance difference may not matter for a library doing a few reflected calls, especially if those calls are mostly to dynamically set up a static structure in memory against which it can make normal calls. But in a dynamic language, where every call must use these mechanisms, it&#39;s a severe performance hit.

http://blog.headius.com/2008/09/first-taste-of-invokedynamic.html

So, for Java programmer it is essentially useless. Am I right? From this point of view, It can be only considered as alternative way for Core Reflection API.

**UPDATE-2020:** Indeed, MethodHandle can be thought as s more powerful alternative to Core Reflection API. Starting with JDK 8 there are also Java Language features that use it.

MethodHandle - What is it all about?

On this Oracle page [Java HotSpot VM Options][1], it lists `-XX:+UseCompressedStrings` as being available and on by default.  However in Java 6 update 29, it is off by default and in Java 7 update 2 it reports a warning

    Java HotSpot(TM) 64-Bit Server VM warning: ignoring option UseCompressedStrings; support was removed in 7.0

Does anyone know the thinking behind removing this option?

---

https://stackoverflow.com/questions/8832822/sorting-lines-of-an-enormous-file-txt-in-java/8833257#8833257 

With `-mx2g`, this example took 4.541 seconds with the option on and 5.206 second with it off in Java 6 update 29. It is hard to see that it impacts performance.

Note: Java 7 update 2 requires 2.0 G whereas Java 6 update 29 without compressed strings requires 1.8 GB and with compressed string requires only 1.0 GB.


  [1]: http://www.oracle.com/technetwork/java/javase/tech/vmoptions-jsp-140102.html

Support for Compressed Strings being Dropped in HotSpot JVM?

First of all, I have a box with 8gb of ram, so I doubt total memory is the issue.
This application is running fine on machines with 6gb or less.

I am trying to reserve 3GB of space using -Xmx3G under &quot;VM Arguments&quot; in Run Configurations in Eclipse.

Every time I try to reserve more than 1500mb, I get this error:
“Error occurred during initialization of VM; Could not reserve enough space for object heap” using -Xmx3G

What is going on here?

“Error occurred during initialization of VM; Could not reserve enough space for object heap” using -Xmx3G

Specifically, why would it help to fix a PermGen OutOfMemoryError issue?

Also, bonus points for an answer that points me to the documentation on JVM arguments...

What does -XX:MaxPermSize do?

I&#39;m using IDEA 12 Leda on Mountain Lion. I wanted to increase the maximum memory that IDE can use. I set the VMOptions in Info.plist file to be
`-Xmx2048m -ea -XX:+HeapDumpOnOutOfMemoryError -Xverify:none -Xbootclasspath/a:../lib/boot.jar`

When I open up IDEA, I still see the maximum memory to be 711m.

`jps -v` shows my VMOptions has been loaded but it&#39;s replaced by the following options.

    29388  **-Xmx2048m** -ea -XX:+HeapDumpOnOutOfMemoryError -Xverify:none -Xbootclasspath/a:../lib/boot.jar -Xms128m **-Xmx800m** -XX:MaxPermSize=350m -XX:ReservedCodeCacheSize=64m -XX:+UseCodeCacheFlushing -XX:+UseCompressedOops -Didea.paths.selector=IdeaIC12 -Dsun.java2d.noddraw=true -Didea.max.intellisense.filesize=2500 -Didea.dynamic.classpath=false -Didea.jars.nocopy=false -Dsun.java2d.d3d=false -Dapple.awt.fullscreencapturealldisplays=false -Dapple.laf.useScreenMenuBar=true -Djava.endorsed.dirs= -Dswing.bufferPerWindow=false -Didea.fatal.error.notification=enabled -Didea.cycle.buffer.size=1024 -Didea.popup.weight=heavy -Didea.xdebug.key=-Xdebug -Dapple.awt.graphics.UseQuartz=true -Dsun.java2d.pmoffscreen=false -Didea.no.launcher=false -DCVS_PASSFILE=~/.cvspass -Didea.use.default.antialiasing.in.editor=false -Dcom.apple.mrj.application.live-resize=false -Didea.smooth.progress=false
    29392 Jps -Dapplication.home=/System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home -Xms8m

Where does `-Xmx800` come from? I need to remove it.

How to increase IDE memory limit in IntelliJ IDEA on Mac?

I tried searching the internet about -Xmn option, without success.

Can someone please explain what this stands for and how can I use it to tune JVM? 


What does -Xmn jvm option stands for

I thought it would be great to have a comparison between `_JAVA_OPTIONS` and `JAVA_TOOL_OPTIONS`.
I have been searching a bit for one, but I cannot find anything, so I hope we can find the knowledge here on Stackoverflow.

`JAVA_OPTS` is included for completeness. It is not part of the JVM, but there is a lot of questions about it out in the wild.

What I know:
------

So far I have found out that:

 - **`JAVA_OPTS`** is not used by the JDK, but by a bunch of other apps (see [this post][1]).
 - **`JAVA_TOOL_OPTIONS`** and **`_JAVA_OPTIONS`** are ways to specify JVM arguments as an environment variable instead of command line parameters. 
   - The are picked up by at least `java` and `javac`
   - They have this precedence:
     1. `_JAVA_OPTIONS` (overwrites the others)
     2. Command line parameters
     3. `JAVA_TOOL_OPTIONS` (is overwritten by the others)

What I would like to know
------

 - Are there any official documentation comparing `JAVA_TOOL_OPTIONS` and `_JAVA_OPTIONS`
 - Are there any other differences between `JAVA_TOOL_OPTIONS` and `_JAVA_OPTIONS` (except from precedence).
 - Which executables pick up `JAVA_TOOL_OPTIONS` and `_JAVA_OPTIONS` (in addition to `java` and `javac`)
 - Any limitation on what can be included on `JAVA_TOOL_OPTIONS` and `_JAVA_OPTIONS`

Official Documentation
------

I have not been able to find any documentation about `_JAVA_OPTIONS`. [The documentation for `JAVA_TOOL_OPTIONS`][2] does not shed much light on the difference:

&gt; Since the command-line cannot always be accessed or modified, for example in embedded VMs or simply VMs launched deep within scripts, a JAVA_TOOL_OPTIONS variable is provided so that agents may be launched in these cases. &lt;br&gt;...


Example script
====
This is the code I used to figure this out. Console output is included as comments:

	export JAVA_OPTS=foobar
	export JAVA_TOOL_OPTIONS= 
	export _JAVA_OPTIONS=&quot;-Xmx512m -Xms64m&quot;

	java -version                          
	# Picked up JAVA_TOOL_OPTIONS: 
	# Picked up _JAVA_OPTIONS: -Xmx512m -Xms64m
	# java version &quot;1.7.0_40&quot;
	OpenJDK Runtime Environment (IcedTea 2.4.1) (suse-3.41.1-x86_64)
	OpenJDK 64-Bit Server VM (build 24.0-b50, mixed mode)

	javac -version
	# Picked up JAVA_TOOL_OPTIONS: 
	# Picked up _JAVA_OPTIONS: -Xmx512m -Xms64m
	# javac 1.7.0_40

	export JAVA_TOOL_OPTIONS=&quot;-Xmx1 -Xms1&quot;
	export _JAVA_OPTIONS=&quot;-Xmx512m -Xms64m&quot;
	javac -version
	# Picked up JAVA_TOOL_OPTIONS: -Xmx1 -Xms1
	# Picked up _JAVA_OPTIONS: -Xmx512m -Xms64m
	# javac 1.7.0_40

	export JAVA_TOOL_OPTIONS=&quot;-Xmx512m -Xms64m&quot;
	export _JAVA_OPTIONS=&quot;-Xmx1 -Xms1&quot;
	javac -version
	# Picked up JAVA_TOOL_OPTIONS: -Xmx512m -Xms64m
	# Picked up _JAVA_OPTIONS: -Xmx1 -Xms1
	# Error occurred during initialization of VM
	# Too small initial heap

	export JAVA_TOOL_OPTIONS=&quot;-Xmx1 -Xms1&quot;
	export _JAVA_OPTIONS=
	java -Xmx512m -Xms64m -version
	# Picked up JAVA_TOOL_OPTIONS: -Xmx1 -Xms1
	# Picked up _JAVA_OPTIONS: 
	# java version &quot;1.7.0_40&quot;
	# OpenJDK Runtime Environment (IcedTea 2.4.1) (suse-3.41.1-x86_64)
	# OpenJDK 64-Bit Server VM (build 24.0-b50, mixed mode)

	export JAVA_TOOL_OPTIONS=
	export _JAVA_OPTIONS=&quot;-Xmx1 -Xms1&quot;
	java -Xmx512m -Xms64m -version
	# Picked up JAVA_TOOL_OPTIONS: 
	# Picked up _JAVA_OPTIONS: -Xmx1 -Xms1
	# Error occurred during initialization of VM
	# Too small initial heap



  [1]: https://stackoverflow.com/questions/3933300/
  [2]: http://docs.oracle.com/javase/8/docs/platform/jvmti/jvmti.html#tooloptions

Content Type	Original Author	Original Content on Stackoverflow
Question	Rich	View Question on Stackoverflow
Solution 1 - Jvm	Andriy Plokhotnyuk	View Answer on Stackoverflow

Default values for Xmx, Xms, MaxPermSize on non-server-class machines

Jvm Problem Overview

Jvm Solutions

Solution 1 - Jvm

iOS 5 does not allow to store downloaded data in Documents directory?

Maximum characters in labels (table names, columns etc)

Attributions