The final thing to note. If yes where this can be find. On Solaris 9 or higher the one-to-one model is the default and you do not need to do anything. In either case, where can we find this information? The rest of the. Any person s reading the material on this website should consult their own professional investment. An important factor to consider is the decay of time.
This FAQ answers common questions about Java HotSpot Technology and about performance in general. Unless otherwise noted, all information on this page applies to both put options call options difference 64 HotSpot Client VM and the HotSpot Server VM as of Java SE version 1. What command-line options does the Java HotSpot VM provide for performance tuning? See the document Java HotSpot VM Options. Are there any resources for troubleshooting HotSpot issues? For more in-depth troubleshooting discussion beyond the scope of this FAQ, please see the Java Trouble-Shooting and Diagnostic Guide I can't get profiling to work, what should I do?
If you are still having problems please see the Java Trouble-Shooting and Diagnostic Guide I keep running out of file descriptors, what should I do? Certain applications will use a lot of file descriptors. The only thing that you can do is to set the number of file descriptors allowed on the system higher. The hard limit default is and the soft limit default is There are several things to try in this arena.
First, give -Xincgc a try. This uses the incremental garbage collection algorithm, which attempts to collect a fraction of the heap instead of the entire thing at once. For most programs this results in shorter pauses, although throughput is usually worse. Next, you might try decreasing the amount of heap used. A larger heap will cause garbage collection pauses to increase because there is more heap to scan.
For some applications a very large eden helps, for others it will increase the times of minor collections. For most programs, collecting eden is much faster than other generations because most objects die young. Using the above as an example, you can do the following in 1. Many systems have less efficient memory management than in HotSpot. To work around this, some programs keep an "object pool", saving previously allocated objects in some freelist-like data structure and reusing them instead of allocating new ones.
Don't use object pools! Using object pools will fool the collector into thinking objects are live when they really aren't. This may have worked before exact garbage collection became popular, but this is just not a good idea for any modern Java Virtual Machines. See also Tuning Garbage Collection with the 5. How do I profile heap usage? For more information, see jmap - Memory Map and Java Trouble-Shooting and Diagnostic Guide The VM prints "OutOfMemoryError" and exits.
Increasing max heap size doesn't help. The Java HotSpot VM cannot expand its heap size if memory is completely allocated and no swap space is available. This can occur, for example, when several applications are running simultaneously. When this happens, the VM will exit after printing a message similar to the following. For more information, see the evaluation section of bug Why can't I get a larger heap with the bit JVM? The maximum theoretical heap limit for the bit JVM is 4G. Due to various additional constraints such as available swap, kernel address space usage, memory fragmentation, and VM overhead, in practice the limit can be much lower.
On most modern bit Windows systems the maximum heap size will range from 1. On bit Solaris kernels the address space is limited to 2G. On bit operating systems running the bit VM, the max heap size can be higher, approaching 4G on many Solaris systems. If your application requires a very large heap you should use a bit VM on a version of the operating system that supports bit applications.
See Java SE Supported System Configurations for details. Should I pool objects to help GC? Should I call System. Pooling objects will cause them to live longer than necessary. The garbage collection methods will be much more efficient if you let it do the memory management. We strongly advise taking out object pools. If you are having problems with the pause times for garbage collection or it taking too long, then see the pause time question above. What determines when softly referenced objects are flushed?
The default value is one second of lifetime per free megabyte in the heap. This value can be adjusted using the -XX:SoftRefLRUPolicyMSPerMB flag, which accepts integer values representing milliseconds. For example, to change the value from one second to 2. This means that the general tendency is for the Server VM to grow the heap rather than flush soft references, and -Xmx therefore has a significant effect on when soft references are garbage collected.
On the other hand, the Client VM will have a greater tendency to flush soft references rather than grow the heap. The behavior described above is true for 1. This behavior is not part of the VM specification, however, and is subject to change in future releases. Likewise the -XX:SoftRefLRUPolicyMSPerMB flag is not guaranteed to be present in any given release. I'm getting lots of full GC's when I turn on -verbose:gc at regular intervals, I've tuned the heap and it makes no difference, what's going on?
If you're using RMI, then you could be running into distributed GC. Also, some applications are adding explicit GC's thinking that it will make their application faster. Luckily, you can disable this with a command line option in 1. What's the difference between the -client and -server systems? These two systems are different binaries. They are essentially two different compilers JITs interfacing to the same runtime system. The client system is optimal for applications which need fast startup times or small footprints, the server system is optimal for applications where the overall performance is most important.
In general the client system is better suited for interactive applications such as GUIs. Some of the other differences include the compilation policy,heap defaults, and inlining policy. Where do I get the server and client systems? Client and server systems are both downloaded with the bit Solaris and Linux downloads. For bit Windows, if you download the JRE, you get only the client, you'll need to download the SDK to get both systems. For bit, only the server system is included. On Solaris, the bit JRE is an overlay on top of the bit distribution.
However, on Linux and Windows, it's a completely separate distribution. I would like java to default to -server. Put options call options difference 64 have a lot of scripts which I cannot change or do not want to change. Is there any way to do this? Since Java SE 5. The definition of a server-class machine may change from release to release, so please check the appropriate ergonomics document for the definition for your release.
Should I warm up my loops first put options call options difference 64 that Hotspot will compile them? Warming up loops for HotSpot is not necessary. HotSpot contains On Stack Replacement technology which will compile a running interpreted method and replace it while it is still running in a loop. No need to waste your applications time warming up seemingly infinite or very long running loops in order to get better application performance.
What is bit Java? A bit capable J2SE is an implementation of the Java SDK and the JRE along with it that runs in the bit environment of a bit OS on a bit processor. You can think of this environment as being just another platform to which we've ported the SDK. The primary advantage of running Java in a bit environment is the larger address space.
This allows for a much larger Java heap size and an increased maximum number of Java Threads, which is needed for certain kinds of large or long-running applications. The primary complication in doing such a port is that the sizes of some native data types are changed. Not surprisingly the size of pointers is increased to 64 bits. On Solaris and most Unix platforms, the size of put options call options difference 64 C language long is also increased to 64 bits.
Any native code in the bit SDK implementation that relied on the old sizes of these data types is likely to require updating. Within the parts of the SDK written in Java things are simpler, since Java specifies the sizes of its primitive data types precisely. However even some Java code needs updating, such as when a Java int is used to store a value passed to it from a part of the implementation written in C.
This is not true. We did not increase the size of Java integers from 32 to 64 and since Java longs were already 64 bits wide, they didn't need updating. Array indexes, which are defined in the Java Virtual Machine Specification, are not widened from 32 to Which platforms and Java releases support bit operation? In order to run a bit version of Java you must have a processor and operating system that can support the execution of bit applications.
The tables below list the supported bit operating systems and CPUs for J2SE 1. Where can I download the bit SDK or JRE? For the Solaris bit packages, you must first install the bit SDKor JRE and then select and install the bit package on top of the bit version. For all other platforms, you need onlyinterested in. The options -d32 and -d64 have been added to the Java launcher to specify whether the program is to be run in a 32 or bit environment.
On Solaris these correspond to the ILP32 and LP64 data models, respectively. Since Solaris has both a 32 and bit J2SE implementation contained within the same installation of Java, you can specify either version. If neither -d32 put options call options difference 64 -d64 is specified, the default is to run in a bit environment. Other Java commands javac, javadoc, etc. All other platforms Windows and Linux contain separate 32 and bit installation packages. If both packages are installed on a system, you select one or the other by adding the appropriate "bin" directory to your path.
For consistency, the Java implementations on Linux accept the -d64 option. Are both -client and -server VM modes available in bit Java? Currently only the Java HotSpot Server VM supports bit operation, and the -server option is implicit with the use of -d This is subject to change in a future release. Which components do not support bit operation? The Java Plug-in, AWT Robot and Java Web Start currently do not support bit operation.
Use bit Java if you require these features. How is native code affected? There are no changes to public native interfaces JNI, the AWT Native Interface, JPDA for bit development. When porting bit native code to bit Java platforms, you will need to modify you code to be bit clean. Long data types are also troublesome when porting bit code. Windows bit platforms define longs to be 4 bytes but most Unix operating systems specify that longs are 8 bytes in size. For more details, refer to the links below under learning more about bit programming.
When writing Java code, how do I distinguish between 32 and bit operation? There's no public API that allows you to distinguish between 32 and bit operation. Think of bit as just another platform in the write once, run anywhere tradition. Will bit native code work with a bit VM? All native binary code that was written for a bit VM must be recompiled for use in a bit VM. All currently supported operating systems do not allow the mixing of 32 and bit binaries or libraries within a single process.
You can run a bit Java process on the same system as a bit Java process but you cannot mix 32 and bit native libraries. Where can I learn more about bit programming? See the Solaris bit Developer's Guide. The section on converting applications to bit is especially useful. What are the performance characteristics of bit versus bit VMs? Generally, the benefits of being able to address larger amounts of memory come with a small performance loss in bit VMs versus running the same application on a bit VM.
This is due to the fact that every native pointer in the system takes up 8 bytes instead of 4. The loading of this extra data has an impact on memory usage which translates to slightly slower execution depending on how many pointers get loaded during the execution of your Java program. The good news is that with AMD64 and EM64T put options call options difference 64 running in bit mode, the Java VM gets some additional registers which it can use to generate more efficient native instruction sequences.
These extra registers increase performance to the point where there is often no performance loss at all when comparing 32 to bit execution speed. What are the default heap sizes for bit VMs if GC ergonomics is not used? The default heap size for all bit J2SE implementations is 64MB. Remember that Java objects contain class and lock pointers so even if you create Java objects which contain only integers, each object takes up additional memory.
How large a heap can I create using a bit VM? See also Why can't I get a larger heap with the bit JVM? Which garbage collector should I use for a very large bit heaps? The major advantage of a bit Java implementation is to be able to create and use more Java objects. It is great to be able to break these 2GB limits. Remember, however, that this additional heap must be garbage collected at various points in your application's life span.
This additional garbage collection can cause large pauses in your Java application if you do not take this into consideration. The Hotspot VM has a number of garbage collection implementations which are targetted at Java applications with large heaps. We recommend enabling one of the Parallel or Concurrent garbage collectors when running with very large heaps. These collectors attempt to minimize the overhead of collection time by either collecting garbage concurrent with the execution of your Java application or by utilizing multiple CPUs during collections to ge the job done faster.
For information on tuning applications with many threads on Solaris, please see Java and Solaris Threads Document There is an undocumented option, -Xconcurrentio, which generally helps programs with many threads, particularly on Solaris. The main feature turned on with -Xconcurrentio is to use LWP based synchronization instead of thread based synchronization. My application has a lot of threads and is running out of memory, why? You may be running into a problem with the default stack size for threads.
In Java SE 6, the default on Sparc is k in the bit VM, and k in the bit VM. On Windows, the default thread stack size is read from the binary java. As of Java SE 6, this value is k in the bit VM and k in the bit VM. Note that on some versions of Windows, the OS may round up thread stack sizes using very coarse granularity. If the requested size is less than the default size by 1K or more, the stack size is rounded up to the default; otherwise, the stack size is rounded up to a multiple of 1 MB.
Which thread library put options call options difference 64 I use on Solaris 8? Solaris 8 provides 2 versions of the threading library libthread. The default is the T1 library which uses a M:N threading model. The other is the T2 library which uses a model. For more information, please see the following documents: Link 1 What options do I need in order to use the "alternate" one-to-one thread model on Solaris 8 or 9?
On Solaris 9 or higher the one-to-one model is the default and you do not need to do anything. How does the JVM map priorities for Java threads onto native thread priorities in Solaris? Please see the document Thread Priority on the Solaris Platform. My application runs slowly. First, it is important to understand the percentage of time that the application is running bytecodes. The VM technology will only speed up the time spent running in bytecode. For applications where small footprint and fast startup are important, use -client.
For applications where overall performance is the most important, use -server. If the above does not address the performance issue, read on for more tuning parameters you can try, and also see Java HotSpot VM Options. My program isn't scaling with the number of processors. Scaling problems could be a multitude of things.
First, your application may not be written in a scalable manner if you use a lot of synchronization, for one example, or if you have only one thread, as another. It may also be that you are utilizing OS system resources which are not scalable. Finally, if you have many threads, it may be that garbage collection is getting in the way. For more information on GC scalability, see Frequently Asked Questions About Garbage Collection in the Java HotSpot VM and Tuning Garbage Collection with the 5.
The threading model used by the VM may be a problem. For more first millionaire trader of european forex broker jobs on threading model scalability, see Java and Solaris Threads Document How many processors will the HotSpot VM scale to? There are practical limitations to scalability, and often garbage collection will be a bottleneck when large numbers of processors are employed.
Scalability is a top priority for our development team. Currently we run applications on very large systems and we see throughput improvements for those applications which are written in a scalable way. My server application isn't getting faster, why? If your application is using many threads you may be encountering scalability issues. For more information on diagnosing and resolving threading-related scalability issues, please see Java and Solaris Threads Document.
My application uses a database and doesn't seem to scale well. What could be going on? Oracle provides two types of database drivers: a type-2 driver, called the OCI Oracle Call Interface driver that utilizes native code, and a type-4 pure Java driver called the thin driver. In single processor environments, the thin driver works somewhat better than the OCI driver because of the JNI overhead associated with the OCI driver.
On multi-processor configurations, synchronization points within Solaris used by the OCI driver become big bottlenecks and prevent scaling. Put options call options difference 64 way to resolve the sync issue is to use libumem on Solaris. Otherwise, we recommend using the thin driver. I write a simple loop to time a simple operation and it's slow. What am I doing wrong? Here's my program: Remember how HotSpot works. It starts by running your program with an interpreter.
When it discovers that some method is "hot" -- that is, executed a lot, either because it is called a lot or because it contains loops that loop a lot -- it sends that method off to be compiled. After that one of two things will happen, either the next time the method is called the compiled version will be invoked instead of the interpreted version or the currently long running loop will be replaced, while still running, with the compiled method. The latter is known as "on stack replacement", or OSR.
See also the JavaOne presentation S How NOT To Write A Microbenchmark I'm trying to time method invocation time. I don't want there to be any extra work done, so I'm using an empty method. But when I run with HotSpot I forex exchange exchange in bank of china times that are unbelievably fast. Here's my code: Empty methods don't count. And you are also seeing that generated code is sensitive to alignment.
The call to the empty method is being inlined away, so ava metatrader tutorial zotero really is no call there to time. Small methods will be inlined by the compiler at their call sites. This reduces the overhead of calls to small methods. This is particularly helpful for the accessor methods use to provide data abstraction.
If the method is actually empty, the inlining completely removes the call. Code is generated into memory and executed from there. The way the code is laid out in memory makes a big difference in the way it executes. In this example on my machine, the loop that claims to call the method is better aligned and so runs faster than the loop that's trying to figure out how long it takes to run an empty loop, so I get negative numbers for methodTime-loopTime.
Okay, so I'll put some random code in the body of the method so it's not empty and the inlining can't just remove it. Here's my new method and the call site is changed to call method 17 : In the method above, the local variable is never used, so there's no reason to compute its value. So then the method body is empty again and when the code gets compiled and inlined, because we removed enough code to make it small enough for inlining it turns into an empty method again.
This can be surprising to people not used to dealing with optimizing compilers, because they can be fairly clever about discovering and eliminating dead code. They can occasionally be fairly stupid about it, so don't count on the compiler to do arbitrary optimizations of your code. Dead code elimination also extends to control flow. If the compiler can see that a particular "variable" is in fact a constant at a test, it may choose not to compile code for the branch that will never be executed.
This makes it tricky to make microbenchmarks "tricky enough" to actually time what you think you are timing. Dead code elimination is quite useful in real code. Not that people intentionally write dead put options call options difference 64 but often the compiler discovers dead code due to inlining where constants e. I'm trying to benchmark object allocation and garbage collection. So I have harness like the one above, but the body of the method is: That's the optimal case for the HotSpot storage manager.
You will get numbers that are unrealistically good. You are allocating objects that need no initialization and dropping them on the floor instantly. No, the compiler is not smart enough to optimize away the allocation. Real programs do allocate a fair number of short-lived temporary objects, but they also hold on to some objects for longer than this simple test program. The HotSpot storage manager does more work for the objects that are retained for longer, so beware of trying to scale up numbers from tests like this to real systems.
I have a graphics-intensive or GUI-based program. Why isn't HotSpot making my graphics code go faster? The virtual machine is responsible for byte code execution, storage allocation, thread synchronization, etc. Running with the virtual machine are native code libraries that handle input and output through the operating system, especially graphics operations through the window system. Programs that spend significant portions of their time in those native code libraries will not see their performance on HotSpot improved as much as programs that spend most of their time executing byte codes.
This observation about native code applies to other native libraries or any native code libraries that you happen to use with your application. What do you recommend for benchmarking HotSpot, or any virtual machine? The best answer here is to use real applications for benchmarking, as they are the only thing that makes a real difference. If that's not possible, use standard SPEC benchmarks followed by other well respected industry benchmarks.
Microbenchmarks should be avoided, or at least used with much caution. It's very common for microbenchmarks to give misleading answers due to optimization effects. We like to use the SPECjbb benchmark. We use it put options call options difference 64 tracking our own progress over time, and we use it for comparing ourselves to other virtual machines. SPECjbb Java Server Benchmark is SPEC's benchmark for evaluating the performance of server side Java.
The benchmark exercises the implementations of the JVM Java Virtual MachineJIT Just-In-Time compiler, garbage collection, threads and some aspects of the operating system. It also measures the performance of CPUs, caches, memory hierarchy and the scalability of shared memory processors SMPs. SPECjbb provides a new enhanced workload, implemented in a more object-oriented manner to reflect how real-world applications are designed and introduces new features such as XML processing and BigDecimal computations to make the benchmark a more realistic reflection of today's applications.
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