Because that, the same Object may occupy more space too. 64-bits use native datatypes with more capacity but occupy more space.64-bits JVMs can allocate (can use) more memory than the 32-bits ones.32-bits and 64-bits JVMs use different native data type sizes and memory-address spaces. On the one hand, as other mentioned, the memory and data types. One has been mentioned here but not the other. I think there are two main differences to consider. 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. In applications where latency is not crucial and youĬan optimize for throughput only this might be OK, but on most cases Tuning and measuring you can easily introduce full GC pauses spanning What it means in real life is that you have to beĮxtra cautious when building heaps larger than 12-16GB. Means there is more work to be done by GC while cleaning it up from Problem 2: Longer garbage collection pauses. Into one of our earlier posts for more information about calculating This definitely adds some overhead compared to the 8īytes on headers on 32-bit and 4 bytes on references. Secondly, object referencesĬan be either 4 bytes or 8 bytes, depending on JVM flags and the size Object headers are 12 bytes on 64-bit JVM. Why so? Mainlyīecause of the memory layout in 64-bit architecture. Problem 1: 30-50% of more heap is required on 64-bit. For WebSphere Liberty Profile specifically, you are also limited to 2GB.Ħ4-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. Why?įor some Java EE servers that are licensed for production use, it would depend on some factors like which machine how many cores etc. That being said for integration to production, I would recommend 32-bit if it is possible. Primarily because I would likely need the whole memory space for builds and the IDE. The CPU is 圆4 capable, the OS is too, so I like the JVM to run in 64-bit mode as well.ĭepending on context, for local development I will always use a 64-bit JDK. Compressed oops are not free: there is a small computational cost to achieve this big reduction in memory consumption.Īs a personal preference, I always run the 64-bit JVM at home. 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). This is why Oracle introduced "Compressed oops". JVM heap sizes (specified with -Xmx) in 64-bit mode can be huge.īut 64-bit mode comes with a cost: references are double the size, increasing memory consumption. 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. 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 32-bit mode, references are four bytes, allowing the JVM to uniquely address 2^32 bytes of memory. 32-bit really boils down to the size of object references, not the size of numbers. I'm sure I'm missing something here besides not being able to install a 64 bit JRE onto a 32 bit system.Ħ4-bit vs. 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? and I do know that int is a 32 bits and long is 64 bits. 32bit - it really boils down to how the numbers are stored underneath the covers. 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).įrom my understanding of 64bit vs. This prompted an unusual question today, does it matter if I use the 32bit or 64bit JRE bundle?įrom thinking back on it, I've installed both versions before and my normal toolchain plugs happily in (Eclipse). 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.
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