I've been using Java for a while now, and my typical ritual of setting up a new dev machine requires the norm of downloading and installing the latest JDK from Oracle's site. This prompted an unusual question today, does it matter if I use the 32bit or 64bit JRE bundle? From thinking back on it, I've installed both versions before and my normal toolchain plugs happily in (Eclipse). In my day-to-day programming, I do not recall ever having to change something or think about something in a different way just because I was using the 64bit JRE (or targetting the 64bit JRE for that respect). From my understanding of 64bit vs. 32bit - it really boils down to how the numbers are stored underneath the covers. And I do know that int is a 32 bits and long is 64 bits.
Same with float being 32 bits and double is 64 bits - so is it just that Java has abstracted even this subtlety away, and perhaps has been '64 bit compatible' all along? I'm sure I'm missing something here besides not being able to install a 64 bit JRE onto a 32 bit system.
32-bit really boils down to the size of object references, not the size of numbers. In 32-bit mode, references are four bytes, allowing the JVM to uniquely address 2^32 bytes of memory.
This is the reason 32-bit JVMs are limited to a maximum heap size of 4GB (in reality, the limit is smaller due to other JVM and OS overhead, and differs depending on the OS). In 64-bit mode, references are (surprise) eight bytes, allowing the JVM to uniquely address 2^64 bytes of memory, which should be enough for anybody. JVM heap sizes (specified with -Xmx) in 64-bit mode can be huge. But 64-bit mode comes with a cost: references are double the size, increasing memory consumption. This is why Oracle introduced. With compressed oops enabled (which I believe is now the default), object references are shrunk to four bytes, with the caveat that the heap is limited to four billion objects (and 32GB Xmx). Compressed oops are not free: there is a small computational cost to achieve this big reduction in memory consumption.
As a personal preference, I always run the 64-bit JVM at home. The CPU is x64 capable, the OS is too, so I like the JVM to run in 64-bit mode as well.
I think there are two main differences to consider. One has been mentioned here but not the other. On the one hand, as other mentioned, the memory and data types. 32-bits and 64-bits JVMs use different native data type sizes and memory-address spaces. 64-bits JVMs can allocate (can use) more memory than the 32-bits ones. 64-bits use native datatypes with more capacity but occupy more space.
Because that, the same Object may occupy more space too. For JVMs which the Garbage Collector (GC) freezes the machine, the 64-bits versions may be slower because the GC must check bigger heaps/objects and it takes more time. There is an explaining these differences. And on the other hand, the supported native libraries. Java programs that use JNI to access native libraries require different versions depending on the type of JVM.
32-bits JVMs use 32-bits native libraries and 64-bits JVMs use 64bits libraries. That means that, if your program uses libraries that rely on native code such as SWT, you will need different versions of them. Note in the, there are different versions for Linux/Windows 32- and 64-bits. Note that there are (each one with a different version of SWT) for 32- and 64-bits. Some applications, such as Alloy, are packaged with 32-bits native libraries. They fail with 64-bit JVMs.
You can solve these problems just downloading the corresponding 64-bits native libraries and configuring the JNI appropriately. That's not quite as efficient as x32, where limiting all pointers to be in the low 32 bits of address space lets you use them by just zero-extending them. Java goes for some extra overhead in 'decoding' (left shift by 3 and add to heap base). But fortunately an x86 addressing mode can do base + index.8, so it should be pretty efficient to dereference, and only take an extra instruction to compare with a non-encoded pointer. And of course it costs extra when encoding.
Anyway, looks like a sensible tradeoff for Java, since they don't want to limit the heap to 4GB. – Aug 8 '17 at 6:02. What do you mean by 'native datatypes'? Do you mean Java data types like int, long, char and so on? Or are you referring to some native C code inside the JVM itself? The latter is mostly irrelevant since the vast majority of your memory use will usually be part of the Java heap whose data types mostly haven't changed sizes (with a caveat about references).
Most important native data types (which, really) probably don't change sizes too: certainly if you're doing a lot of off-heap stuff or have native code you can choose to keep the data types the same size. – Aug 8 '17 at 19:42. Depending on context, for local development I will always use a 64-bit JDK. Primarily because I would likely need the whole memory space for builds and the IDE. That being said for integration to production, I would recommend 32-bit if it is possible. For some Java EE servers that are licensed for production use, it would depend on some factors like which machine how many cores etc.
For WebSphere Liberty Profile specifically, you are also limited to 2GB. 64-bit JREs would take up slightly more memory and if you're trying to constrain it to something like 2GB or better yet 2x 1GB cluster you would have more flex space to work around in without paying a cent.
From Problem 1: 30-50% of more heap is required on 64-bit. Mainly because of the memory layout in 64-bit architecture. First of all – object headers are 12 bytes on 64-bit JVM. Secondly, object references can be either 4 bytes or 8 bytes, depending on JVM flags and the size of the heap. This definitely adds some overhead compared to the 8 bytes on headers on 32-bit and 4 bytes on references.
You can also dig into one of our earlier posts for more information about calculating the memory consumption of an object. Problem 2: Longer garbage collection pauses. Building up more heap means there is more work to be done by GC while cleaning it up from unused objects. What it means in real life is that you have to be extra cautious when building heaps larger than 12-16GB. Without fine tuning and measuring you can easily introduce full GC pauses spanning several minutes. In applications where latency is not crucial and you can optimize for throughput only this might be OK, but on most cases this might become a showstopper. To limit your impact for your Java EE environment, offload parts of it to other microservices such as ElasticSearch for search, Hazelcast for caching, your database for data storage and keep your Java EE server to host your application core itself rather than running the services inside it.
I've been using Java for a while now, and my typical ritual of setting up a new dev machine requires the norm of downloading and installing the latest JDK from Oracle's site. This prompted an unusual question today, does it matter if I use the 32bit or 64bit JRE bundle? From thinking back on it, I've installed both versions before and my normal toolchain plugs happily in (Eclipse). Console Humidifiers.
In my day-to-day programming, I do not recall ever having to change something or think about something in a different way just because I was using the 64bit JRE (or targetting the 64bit JRE for that respect). From my understanding of 64bit vs.
32bit - it really boils down to how the numbers are stored underneath the covers. And I do know that int is a 32 bits and long is 64 bits. Same with float being 32 bits and double is 64 bits - so is it just that Java has abstracted even this subtlety away, and perhaps has been '64 bit compatible' all along? I'm sure I'm missing something here besides not being able to install a 64 bit JRE onto a 32 bit system. 32-bit really boils down to the size of object references, not the size of numbers.
In 32-bit mode, references are four bytes, allowing the JVM to uniquely address 2^32 bytes of memory. This is the reason 32-bit JVMs are limited to a maximum heap size of 4GB (in reality, the limit is smaller due to other JVM and OS overhead, and differs depending on the OS). In 64-bit mode, references are (surprise) eight bytes, allowing the JVM to uniquely address 2^64 bytes of memory, which should be enough for anybody. JVM heap sizes (specified with -Xmx) in 64-bit mode can be huge. But 64-bit mode comes with a cost: references are double the size, increasing memory consumption.
This is why Oracle introduced. With compressed oops enabled (which I believe is now the default), object references are shrunk to four bytes, with the caveat that the heap is limited to four billion objects (and 32GB Xmx). Compressed oops are not free: there is a small computational cost to achieve this big reduction in memory consumption. As a personal preference, I always run the 64-bit JVM at home. The CPU is x64 capable, the OS is too, so I like the JVM to run in 64-bit mode as well. I think there are two main differences to consider. One has been mentioned here but not the other.
On the one hand, as other mentioned, the memory and data types. 32-bits and 64-bits JVMs use different native data type sizes and memory-address spaces. 64-bits JVMs can allocate (can use) more memory than the 32-bits ones. 64-bits use native datatypes with more capacity but occupy more space. Because that, the same Object may occupy more space too. For JVMs which the Garbage Collector (GC) freezes the machine, the 64-bits versions may be slower because the GC must check bigger heaps/objects and it takes more time. There is an explaining these differences.
And on the other hand, the supported native libraries. Java programs that use JNI to access native libraries require different versions depending on the type of JVM. 32-bits JVMs use 32-bits native libraries and 64-bits JVMs use 64bits libraries. That means that, if your program uses libraries that rely on native code such as SWT, you will need different versions of them.
32 Bit Java Jre For Jpcsp
Note in the, there are different versions for Linux/Windows 32- and 64-bits. Note that there are (each one with a different version of SWT) for 32- and 64-bits. Some applications, such as Alloy, are packaged with 32-bits native libraries. They fail with 64-bit JVMs. You can solve these problems just downloading the corresponding 64-bits native libraries and configuring the JNI appropriately.
That's not quite as efficient as x32, where limiting all pointers to be in the low 32 bits of address space lets you use them by just zero-extending them. Java goes for some extra overhead in 'decoding' (left shift by 3 and add to heap base). But fortunately an x86 addressing mode can do base + index.8, so it should be pretty efficient to dereference, and only take an extra instruction to compare with a non-encoded pointer.
And of course it costs extra when encoding. Anyway, looks like a sensible tradeoff for Java, since they don't want to limit the heap to 4GB. – Aug 8 '17 at 6:02. What do you mean by 'native datatypes'? Do you mean Java data types like int, long, char and so on? Or are you referring to some native C code inside the JVM itself?
The latter is mostly irrelevant since the vast majority of your memory use will usually be part of the Java heap whose data types mostly haven't changed sizes (with a caveat about references). Most important native data types (which, really) probably don't change sizes too: certainly if you're doing a lot of off-heap stuff or have native code you can choose to keep the data types the same size. – Aug 8 '17 at 19:42. Depending on context, for local development I will always use a 64-bit JDK. Primarily because I would likely need the whole memory space for builds and the IDE. Undangan nikah format cdr.
That being said for integration to production, I would recommend 32-bit if it is possible. For some Java EE servers that are licensed for production use, it would depend on some factors like which machine how many cores etc. For WebSphere Liberty Profile specifically, you are also limited to 2GB.
64-bit JREs would take up slightly more memory and if you're trying to constrain it to something like 2GB or better yet 2x 1GB cluster you would have more flex space to work around in without paying a cent. From Problem 1: 30-50% of more heap is required on 64-bit.
Mainly because of the memory layout in 64-bit architecture. First of all – object headers are 12 bytes on 64-bit JVM. Secondly, object references can be either 4 bytes or 8 bytes, depending on JVM flags and the size of the heap. This definitely adds some overhead compared to the 8 bytes on headers on 32-bit and 4 bytes on references. You can also dig into one of our earlier posts for more information about calculating the memory consumption of an object.
Problem 2: Longer garbage collection pauses. Building up more heap means there is more work to be done by GC while cleaning it up from unused objects. What it means in real life is that you have to be extra cautious when building heaps larger than 12-16GB.
Without fine tuning and measuring you can easily introduce full GC pauses spanning several minutes. In applications where latency is not crucial and you can optimize for throughput only this might be OK, but on most cases this might become a showstopper. To limit your impact for your Java EE environment, offload parts of it to other microservices such as ElasticSearch for search, Hazelcast for caching, your database for data storage and keep your Java EE server to host your application core itself rather than running the services inside it.