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Java Forum / General / November 2007Can Java access more than 2GB of memory on WIndows 32
I am getting an out of memeory exception error running a java program on Windows 32 bit. Memory on the box is 4GB (I know 32 bit can access up to 4GB but Windows OS reserves 2GB for its own processes. I can increase memory on this box from 4GB to 8GB, but my question is Java capable of accessing this memory. In Windows memory beyond 4GB is accessible using /PAE switch and program has to be wriiten in a ceratin way to use it, that's why my question is whether Java is capable of accessing 8GB memory on Windows 32 bit? >I am getting an out of memeory exception error running a java program > on Windows 32 bit. [quoted text clipped - 5 lines] > a ceratin way to use it, that's why my question is whether Java is > capable of accessing 8GB memory on Windows 32 bit? Java is limited to about 1.5-1.9 GB (YMMV) on Win 32 machines. You have to shift up to 64-bit JVM on the appropriate hardware to get a larger range. Matt Humphrey http://www.iviz.com/ > <zigzag...@yahoo.com> wrote in message > [quoted text clipped - 14 lines] > > Matt Humphreyhttp://www.iviz.com/ Windows OS has /3GB swtch which allows for 3GB user addressable space (instead of 2GB), so I will think java should be able to access close to 3GB (sighlt less than 3GB). I do not know where java heap size parameter comes into play as for as 2GB or 3GB memory per process. > Windows OS has /3GB swtch which allows for 3GB user addressable space > (instead of 2GB), > so I will think java should be able to access close to 3GB (sighlt > less than 3GB). I do > not know where java heap size parameter comes into play as for as 2GB > or 3GB memory per process. Java can not use that extra GB. I assumes it has to do with that Java's memory need to be contiguous and that something small just get in above the 2 GB mark. 64 bit !! Arne > zigzag...@yahoo.com wrote: > > Windows OS has /3GB swtch which allows for 3GB user addressable space [quoted text clipped - 12 lines] > > Arne 3GB swich gives contigous 3GB memory to user address space. Basically in Windows 32 bit, of 4B - 2GB (contigous) is accessible by kernel and other 2GB by user address space. With 3GB switch, kernel uses only 1GB, so user address space has more memory (up to 3GB). This is a soltion to provide more memory if one cannot switch to 64bit which is the best solution. I have used this feature in conjunction with Oracle. It does not require any changes in one's program. I will be really surprised if Java or any other application cannot use it. >> Java can not use that extra GB. >> [quoted text clipped - 14 lines] > program. I will be really surprised if Java or any other application > cannot use it. I know what /3GB does. Read what I write. Java can not use that extra GB. I guess it is because something else it putting something in around the 2 GB mark. Arne > zigzag...@yahoo.com wrote: > >> Java can not use that extra GB. [quoted text clipped - 28 lines] > > - Show quoted text - Arne: Thanks. I am curious where it is documented it cannot use more than 2GB even when /3GB switch is on, just asking. >> Java can not use that extra GB. > Thanks. I am curious where it is documented it cannot use more than > 2GB even when /3GB switch is on, just asking. I do not think I have ever seen an official statement. But Google find a ton of references: http://forum.java.sun.com/thread.jspa?threadID=576811 http://forum.java.sun.com/thread.jspa?threadID=621332 http://www.unixville.com/~moazam/ But when Googling I found this: http://dev2dev.bea.com/blog/hstahl/archive/2005/12/how_to_get_almo.html Sounds as if BEA JVM can handle a split heap and thereby utilize the /3GB switch. Could be wort trying. Arne > zigzag...@yahoo.com wrote: > >> Java can not use that extra GB. [quoted text clipped - 11 lines] > > Arne Arne: Thanks a million. Prem > I am getting an out of memeory exception error running a java program > on Windows 32 bit. [quoted text clipped - 5 lines] > a ceratin way to use it, that's why my question is whether Java is > capable of accessing 8GB memory on Windows 32 bit? Not from a single process (JVM). 64 bit ! Arne > I am getting an out of memeory exception error running a java program > on Windows 32 bit. [quoted text clipped - 5 lines] > a ceratin way to use it, that's why my question is whether Java is > capable of accessing 8GB memory on Windows 32 bit? The Java virtual machine won't necessarily automatically allocate all of your available memory, it has built in minimums and maximums. If you're using Suns JVM, try adding -Xmx512M That sets the max heap size to 512 megs. Experiment with that value. Cation, don't set it too high either, as you'll degrade the performance of your garbage collector.  SignatureDaniel Pitts' Tech Blog: <http://virtualinfinity.net/wordpress/> On Nov 24, 1:16 pm, Daniel Pitts <newsgroup.spamfil...@virtualinfinity.net> wrote: > zigzag...@yahoo.com wrote: > > I am getting an out of memeory exception error running a java program [quoted text clipped - 18 lines] > -- > Daniel Pitts' Tech Blog: <http://virtualinfinity.net/wordpress/> I am somewhat confused wih this switch, my progam is a third party program which uses Apache tomcat, so tomcat5 process is started and my third party application is integerated with tomcat. I see tomcat5 process started and I access third part program's web site, thread count (increases for tomcat5 and memory usgae increases. I will be suprised if tomcat5 cannot access memory up to 2GB. Is max heap size per thread or for enitre jvm (i.e. tomcat5 process). Prem > On Nov 24, 1:16 pm, Daniel Pitts > <newsgroup.spamfil...@virtualinfinity.net> wrote: [quoted text clipped - 31 lines] > > Prem that switch is per JVM, in your startup scripts, you need to tune your memory settings. Java (and therefore tomcat) won't automatically allow all available memory to be allocated, since this would add a performance bottleneck for garbage collection. Tomcat has a memory FAQ: <http://tomcat.apache.org/faq/memory.html> SignatureDaniel Pitts' Tech Blog: <http://virtualinfinity.net/wordpress/> Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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