[OT]RE: Maximum memory that can be assigned to Tomcat on windows platform
See below. I hope MS Outlook does some decent indend so my response is clear -.- -Original Message- From: Christopher Schultz [mailto:ch...@christopherschultz.net] Sent: 30. november 2011 18:51 To: Tomcat Users List Subject: Re: Maximum memory that can be assigned to Tomcat on windows platform -BEGIN PGP SIGNED MESSAGE- Hash: SHA1 Casper, On 11/30/11 3:37 AM, Casper Wandahl Schmidt wrote: Another question to ask is, why do you have 8GB memory when running 32bit? That is just stupid since 32bit cannot address more than 4GB of memory no matter what you do. Any sysadmin should know that right? That's per process. All reasonably recent 32-bit OSs can address way more than 4GiB internally. For example: http://msdn.microsoft.com/en-us/library/windows/desktop/aa366778%28v=vs.85%29.aspx#memory_limits This is generally done through PAE (http://en.wikipedia.org/wiki/Physical_Address_Extension) which allows 32-bit OSs to access more than 4GiB at the kernel level, though each process is still limited to 4GiB. Aha so I learned something new today :) I'm still puzzled as to how a 32 bit CPU can compute and fetch a memory cell with address above 4GB since it cannot hold this large value. Anyway that is just too much low-level computer science for me, all I ever had was a seven week course on architecture and networking (a single week out of the seven) :) -Casper Running a machine with more than 4GiB in 32-bit mode isn't stupid at all IMO. If you have relatively small processes, there's no need for the overhead of 64-bit even if you have 16GiB or more. - -chris -BEGIN PGP SIGNATURE- Version: GnuPG/MacGPG2 v2.0.17 (Darwin) Comment: GPGTools - http://gpgtools.org Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAk7WbQYACgkQ9CaO5/Lv0PBsWwCgnifhHtqrLUBi7K4PeDjp4hnC JMkAn0gilsNy2hv3zu3nzUkrmrzxoYWF =AZpI -END PGP SIGNATURE- - To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org - To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
Re: [OT]RE: Maximum memory that can be assigned to Tomcat on windows platform
Op donderdag, 1 december 2011 09:39 schreef Casper Wandahl Schmidt kalle.pri...@gmail.com: See below. I hope MS Outlook does some decent indend so my response is clear -.- -Original Message- From: Christopher Schultz [mailto:ch...@christopherschultz.net] Sent: 30. november 2011 18:51 To: Tomcat Users List Subject: Re: Maximum memory that can be assigned to Tomcat on windows platform -BEGIN PGP SIGNED MESSAGE- Hash: SHA1 Casper, On 11/30/11 3:37 AM, Casper Wandahl Schmidt wrote: Another question to ask is, why do you have 8GB memory when running 32bit? That is just stupid since 32bit cannot address more than 4GB of memory no matter what you do. Any sysadmin should know that right? That's per process. All reasonably recent 32-bit OSs can address way more than 4GiB internally. For example: http://msdn.microsoft.com/en-us/library/windows/desktop/aa366778%28v=vs.85%29.aspx#memory_limits This is generally done through PAE (http://en.wikipedia.org/wiki/Physical_Address_Extension) which allows 32-bit OSs to access more than 4GiB at the kernel level, though each process is still limited to 4GiB. Aha so I learned something new today :) I'm still puzzled as to how a 32 bit CPU can compute and fetch a memory cell with address above 4GB since it cannot hold this large value. Anyway that is just too much low-level computer science for me, all I ever had was a seven week course on architecture and networking (a single week out of the seven) :) -Casper Running a machine with more than 4GiB in 32-bit mode isn't stupid at all IMO. If you have relatively small processes, there's no need for the overhead of 64-bit even if you have 16GiB or more. - -chris I have an analogy for you. If you look out of your window you only see a small part of the world. If you move your window you wil see another part of the world. This is what the OS does with PAE. It moves the window on your RAM frequently. That is why a 32 bits application only sees max. 4GB. That is the size of its window. Ronald.
RE: [OT]RE: Maximum memory that can be assigned to Tomcat on windows platform
-Original Message- From: Ronald Klop (Mailing List) [mailto:ronald-mailingl...@base.nl] Sent: 1. december 2011 12:06 To: Tomcat Users List Subject: Re: [OT]RE: Maximum memory that can be assigned to Tomcat on windows platform Op donderdag, 1 december 2011 09:39 schreef Casper Wandahl Schmidt kalle.pri...@gmail.com: See below. I hope MS Outlook does some decent indend so my response is clear -.- -Original Message- From: Christopher Schultz [mailto:ch...@christopherschultz.net] Sent: 30. november 2011 18:51 To: Tomcat Users List Subject: Re: Maximum memory that can be assigned to Tomcat on windows platform -BEGIN PGP SIGNED MESSAGE- Hash: SHA1 Casper, On 11/30/11 3:37 AM, Casper Wandahl Schmidt wrote: Another question to ask is, why do you have 8GB memory when running 32bit? That is just stupid since 32bit cannot address more than 4GB of memory no matter what you do. Any sysadmin should know that right? That's per process. All reasonably recent 32-bit OSs can address way more than 4GiB internally. For example: http://msdn.microsoft.com/en-us/library/windows/desktop/aa366778%28v=v s.85%29.aspx#memory_limits This is generally done through PAE (http://en.wikipedia.org/wiki/Physical_Address_Extension) which allows 32-bit OSs to access more than 4GiB at the kernel level, though each process is still limited to 4GiB. Aha so I learned something new today :) I'm still puzzled as to how a 32 bit CPU can compute and fetch a memory cell with address above 4GB since it cannot hold this large value. Anyway that is just too much low-level computer science for me, all I ever had was a seven week course on architecture and networking (a single week out of the seven) :) -Casper Running a machine with more than 4GiB in 32-bit mode isn't stupid at all IMO. If you have relatively small processes, there's no need for the overhead of 64-bit even if you have 16GiB or more. - -chris I have an analogy for you. If you look out of your window you only see a small part of the world. If you move your window you wil see another part of the world. This is what the OS does with PAE. It moves the window on your RAM frequently. That is why a 32 bits application only sees max. 4GB. That is the size of its window. Ronald. That didn't quite help me understand, because how can the OS map from ie. 0-4GB to 4-8GB (the window is moved) when it can only use a 32bit register to tell the machine where to look in the psysical memory, that is where my knowledge ends :) So I read about PAE and found out that it uses 2 registers (36 bits due to some bits being used as flags) and that makes good sense, but how can the cpu calculate an address without overflow and send a command to the bus containing a 36bit address (or whatever fetches the bits from RAM)? That is where I'm puzzled but I guess it is because I'm not at all into ISA-level and below :) -Casper - To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
Re: [OT]RE: Maximum memory that can be assigned to Tomcat on windows platform
On Thu, Dec 1, 2011 at 12:29, Casper Wandahl Schmidt kalle.pri...@gmail.com wrote: [...] That didn't quite help me understand, because how can the OS map from ie. 0-4GB to 4-8GB (the window is moved) when it can only use a 32bit register to tell the machine where to look in the psysical memory, that is where my knowledge ends :) So I read about PAE and found out that it uses 2 registers (36 bits due to some bits being used as flags) and that makes good sense, but how can the cpu calculate an address without overflow and send a command to the bus containing a 36bit address (or whatever fetches the bits from RAM)? That is where I'm puzzled but I guess it is because I'm not at all into ISA-level and below :) It is the role of the MMU to do that. At any one time, it can map a virtual, 32-bit wide, address to a real, 36-bit wide address. It uses TLBs (Translation Lookaside Buffers) for that, and it is the OS' role to have the correct TLB in place at any time. -- Francis Galiegue ONE2TEAM Ingénieur système Mob : +33 (0) 683 877 875 Tel : +33 (0) 178 945 552 f...@one2team.com 40 avenue Raymond Poincaré 75116 Paris - To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
RE: [OT]RE: Maximum memory that can be assigned to Tomcat on windows platform
-Original Message- From: Francis GALIEGUE [mailto:f...@one2team.com] Sent: 1. december 2011 12:33 To: Tomcat Users List Subject: Re: [OT]RE: Maximum memory that can be assigned to Tomcat on windows platform On Thu, Dec 1, 2011 at 12:29, Casper Wandahl Schmidt kalle.pri...@gmail.com wrote: [...] That didn't quite help me understand, because how can the OS map from ie. 0-4GB to 4-8GB (the window is moved) when it can only use a 32bit register to tell the machine where to look in the psysical memory, that is where my knowledge ends :) So I read about PAE and found out that it uses 2 registers (36 bits due to some bits being used as flags) and that makes good sense, but how can the cpu calculate an address without overflow and send a command to the bus containing a 36bit address (or whatever fetches the bits from RAM)? That is where I'm puzzled but I guess it is because I'm not at all into ISA-level and below :) It is the role of the MMU to do that. At any one time, it can map a virtual, 32-bit wide, address to a real, 36-bit wide address. It uses TLBs (Translation Lookaside Buffers) for that, and it is the OS' role to have the correct TLB in place at any time. Nice to know :) That explained it all :) -Casper -- Francis Galiegue ONE2TEAM Ingénieur système Mob : +33 (0) 683 877 875 Tel : +33 (0) 178 945 552 f...@one2team.com 40 avenue Raymond Poincaré 75116 Paris - To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org - To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
RE: [OT]RE: Maximum memory that can be assigned to Tomcat on windows platform
On Thu, 1 Dec 2011 12:29:14 +0100, Casper Wandahl Schmidt wrote: That didn't quite help me understand, because how can the OS map from ie. 0-4GB to 4-8GB (the window is moved) when it can only use a 32bit register to tell the machine where to look in the psysical memory, that is where my knowledge ends :) So I read about PAE and found out that it uses 2 registers (36 bits due to some bits being used as flags) and that makes good sense, but how can the cpu calculate an address without overflow and send a command to the bus containing a 36bit address (or whatever fetches the bits from RAM)? That is where I'm puzzled but I guess it is because I'm not at all into ISA-level and below :) Well, it's rather out of the scope of this list. On the other hand, increasing java heap size is not always the best option. It heavily depends on memory usage pattern in your application. In general: the bigger heap, the longer GC will run. -- Mikolaj Rydzewski m...@ceti.pl - To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
Re: [OT]RE: Maximum memory that can be assigned to Tomcat on windows platform
Mikolaj Rydzewski wrote: On Thu, 1 Dec 2011 12:29:14 +0100, Casper Wandahl Schmidt wrote: That didn't quite help me understand, because how can the OS map from ie. 0-4GB to 4-8GB (the window is moved) when it can only use a 32bit register to tell the machine where to look in the psysical memory, that is where my knowledge ends :) So I read about PAE and found out that it uses 2 registers (36 bits due to some bits being used as flags) and that makes good sense, but how can the cpu calculate an address without overflow and send a command to the bus containing a 36bit address (or whatever fetches the bits from RAM)? That is where I'm puzzled but I guess it is because I'm not at all into ISA-level and below :) Well, it's rather out of the scope of this list. On the other hand, increasing java heap size is not always the best option. It heavily depends on memory usage pattern in your application. In general: the bigger heap, the longer GC will run. Why do I feel that a comment from Chuck is going to follow that one later on ? ;-) - To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
RE: [OT]RE: Maximum memory that can be assigned to Tomcat on windows platform
From: André Warnier [mailto:a...@ice-sa.com] Subject: Re: [OT]RE: Maximum memory that can be assigned to Tomcat on windows platform In general: the bigger heap, the longer GC will run. Not strictly true, and hasn't been true for many years. GC time is proportional to the number of live (reachable) objects, not the size of the heap. If the app is making heavy use of weak references, this may allow more live objects to persist in a larger heap until GC gets fed up with the mess and throws them all away. Why do I feel that a comment from Chuck is going to follow that one later on ? Just had to wake up first. - Chuck THIS COMMUNICATION MAY CONTAIN CONFIDENTIAL AND/OR OTHERWISE PROPRIETARY MATERIAL and is thus for use only by the intended recipient. If you received this in error, please contact the sender and delete the e-mail and its attachments from all computers.
Re: [OT]RE: Maximum memory that can be assigned to Tomcat on windows platform
The OS has little to do with the calculation. The CPU hardware is doing it. The processor's address logic uses registers which are wider than 32 bits. Just as you can add a 1-digit number to a 3-digit number and get a 3-digit result, the widget that maps a process' virtual address space to the hardware's physical address space can add the content of a 32-bit register to the content of a 36-bit register and get a 36-bit result. (I'm ignoring the possibility of overflow, like adding 1 to 999 in a 3-digit field. With good management they can be avoided.) Only a tiny bit of the OS kernel, and nothing in any process, needs to know about physical memory. The hardware is set up by that bit and makes processes, and the rest of the kernel, think they each live in a block of memory that starts at 0 and ends at, say, 3GB. In physical memory they live side-by-side (to oversimplify a bit). For how it does that, track down a little story called The Paging Game. -- Mark H. Wood, Lead System Programmer mw...@iupui.edu Asking whether markets are efficient is like asking whether people are smart. pgpjKSIiRF27q.pgp Description: PGP signature
Re: [OT]RE: Maximum memory that can be assigned to Tomcat on windows platform
On Thu, Dec 01, 2011 at 12:38:01PM +0100, Mikolaj Rydzewski wrote: On the other hand, increasing java heap size is not always the best option. It heavily depends on memory usage pattern in your application. In general: the bigger heap, the longer GC will run. I was thinking that someone should bring this up. When a program uses unexpectedly huge amounts of memory in practice, the *first* thing to consider is: 1. does it actually need that much? 2. ...or is it leaking dynamically created objects? 3. ...or has cheap allocation and garbage collection lured me into doing something suboptimal, like sucking down an entire database table into an array or list and then walking it sequentially, when I could have used an iterator and let the DBMS code work out near-optimal buffering? IOW is my problem fundamentally this big, or is something else going on? -- Mark H. Wood, Lead System Programmer mw...@iupui.edu Asking whether markets are efficient is like asking whether people are smart. pgpIowkiM39ep.pgp Description: PGP signature
Re: [OT]RE: Maximum memory that can be assigned to Tomcat on windows platform
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 Casper, On 12/1/11 3:39 AM, Casper Wandahl Schmidt wrote: Aha so I learned something new today :) I'm still puzzled as to how a 32 bit CPU can compute and fetch a memory cell with address above 4GB since it cannot hold this large value. OS != CPU Also, OS != process While the chips and OSs are officially 32-bit, both are able to handle integers that don't fit into 32-bit registers in various ways. Usually, CPUs have registers that are larger than their architecture would suggest, and uses them even to perform computations on 32-bit data. The real issue here is that in a 32-bit environment, word-sized pointers are 32-bits and therefore an individual process gets a 4GiB maximum process space, which can be mapped-into a much larger space by the kernel, and even by the underlying hardware if it's in on the deal. Anyway that is just too much low-level computer science for me, all I ever had was a seven week course on architecture and networking (a single week out of the seven) :) It never hurts to learn more. Unless your brain is full. Then it *really* hurts. - -chris -BEGIN PGP SIGNATURE- Version: GnuPG/MacGPG2 v2.0.17 (Darwin) Comment: GPGTools - http://gpgtools.org Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAk7YKp0ACgkQ9CaO5/Lv0PDpDgCgwNXVZ1k43CrOFDjcDryl3JTw dSkAoK5XWk47MjE+fbsNnOS3CbGBdjxb =nuE/ -END PGP SIGNATURE- - To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
Re: [OT]RE: Maximum memory that can be assigned to Tomcat on windows platform
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 Mikolaj, On 12/1/11 6:38 AM, Mikolaj Rydzewski wrote: On Thu, 1 Dec 2011 12:29:14 +0100, Casper Wandahl Schmidt wrote: That didn't quite help me understand, because how can the OS map from ie. 0-4GB to 4-8GB (the window is moved) when it can only use a 32bit register to tell the machine where to look in the psysical memory, that is where my knowledge ends :) So I read about PAE and found out that it uses 2 registers (36 bits due to some bits being used as flags) and that makes good sense, but how can the cpu calculate an address without overflow and send a command to the bus containing a 36bit address (or whatever fetches the bits from RAM)? That is where I'm puzzled but I guess it is because I'm not at all into ISA-level and below :) Well, it's rather out of the scope of this list. On the other hand, increasing java heap size is not always the best option. It heavily depends on memory usage pattern in your application. In general: the bigger heap, the longer GC will run. That's a rather sweeping generalization. The heap size doesn't matter directly.. it's the number of objects being managed within that heap that matters. Of course, with a larger heap, you can fit more objects into it before a major collection is required. Generational heap strategies are fairly efficient, and performance depends upon the number of LIVE objects, not just the total number of objects. Oddly enough, most garbage collection is really collecting non-garbage and ignoring the actual garbage. It's a bit like moving to a different house when yours gets too cluttered: you just take the things you want to keep and leave everything else behind. - -chris -BEGIN PGP SIGNATURE- Version: GnuPG/MacGPG2 v2.0.17 (Darwin) Comment: GPGTools - http://gpgtools.org Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAk7YK88ACgkQ9CaO5/Lv0PDzdACgmYJEuWHFNkFyEVWRcucJo4Yu 6uwAoK2JWcjX0SRY6PPIWwd1m7Fhx+f8 =XY04 -END PGP SIGNATURE- - To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
Re: [OT]RE: Maximum memory that can be assigned to Tomcat on windows platform
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 Mark, On 12/1/11 9:50 AM, Mark H. Wood wrote: On Thu, Dec 01, 2011 at 12:38:01PM +0100, Mikolaj Rydzewski wrote: On the other hand, increasing java heap size is not always the best option. It heavily depends on memory usage pattern in your application. In general: the bigger heap, the longer GC will run. I was thinking that someone should bring this up. When a program uses unexpectedly huge amounts of memory in practice, the *first* thing to consider is: 1. does it actually need that much? +1 !! 2. ...or is it leaking dynamically created objects? 3. ...or has cheap allocation and garbage collection lured me into doing something suboptimal, like sucking down an entire database table into an array or list and then walking it sequentially, when I could have used an iterator and let the DBMS code work out near-optimal buffering? IOW is my problem fundamentally this big, or is something else going on? The 2 times our production servers have suffered OOMEs, it's been because we were running with fairly small, (intentionally) restricted heaps (64MiB at first, then 192MiB) and our traffic simply increased beyond our heap size: we had a legitimate reason to increase the heap size (and plenty of physical RAM available to do it). - -chris -BEGIN PGP SIGNATURE- Version: GnuPG/MacGPG2 v2.0.17 (Darwin) Comment: GPGTools - http://gpgtools.org Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAk7YLEwACgkQ9CaO5/Lv0PCGTQCfSwBVBLSKIW2OMjYZWVobxrKY JzkAoJQmi4JK2CHqo23DCuMRGE5Fzq/0 =Qte1 -END PGP SIGNATURE- - To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
[OT] Re: Maximum memory that can be assigned to Tomcat on windows platform
On Wed, Nov 30, 2011 at 18:51, Christopher Schultz ch...@christopherschultz.net wrote: [...] Running a machine with more than 4GiB in 32-bit mode isn't stupid at all IMO. If you have relatively small processes, there's no need for the overhead of 64-bit even if you have 16GiB or more. This is quite the opposite: a 32bit OS has _more_ overhead than a 64bit OS when running on a 64bit CPU. Just consider filesystem calls such as read(), write(), seek(): their arguments are 64bits, not 32, and have been so before 64bit was even common (2+ GB files are common place today). With a 32bit OS on a 64bit CPU, you eat up two registers whereas a 64bit OS will take only one. And of course, this is without considering wasted TLB space or the sheer time to address just one memory page. -- Francis Galiegue ONE2TEAM Ingénieur système Mob : +33 (0) 683 877 875 Tel : +33 (0) 178 945 552 f...@one2team.com 40 avenue Raymond Poincaré 75116 Paris - To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
Re: [OT] Re: Maximum memory that can be assigned to Tomcat on windows platform
Francis GALIEGUE wrote: On Wed, Nov 30, 2011 at 18:51, Christopher Schultz ch...@christopherschultz.net wrote: [...] Running a machine with more than 4GiB in 32-bit mode isn't stupid at all IMO. If you have relatively small processes, there's no need for the overhead of 64-bit even if you have 16GiB or more. This is quite the opposite: a 32bit OS has _more_ overhead than a 64bit OS when running on a 64bit CPU. Just consider filesystem calls such as read(), write(), seek(): their arguments are 64bits, not 32, and have been so before 64bit was even common (2+ GB files are common place today). With a 32bit OS on a 64bit CPU, you eat up two registers whereas a 64bit OS will take only one. And of course, this is without considering wasted TLB space or the sheer time to address just one memory page. I am not knowledgeable at all in such questions, and while you are at it let me ask a question : Does the fact of having a system with a 64-bit CPU (and OS) necessarily (or usually) imply that data transfers between CPU and RAM happen also 64-bit in parallel ? For example, let' suppose that I have an application which handles a very large table of integers (the integers themselves being 2exp31), and that periodically all elements of this table have to be updated. My understanding is that under a 32-bit platform, each integer will occupy 32 bit, while on a 64-bit platform each will occupy 64 bit (the source program remaining the same). If there is not a corresponding 64-bit parallel transfer between CPU and memory, then using a 64-bit CPU would be detrimental, no ? Or is this a non-sensical case nowadays ? - To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
RE: [OT] Re: Maximum memory that can be assigned to Tomcat on windows platform
Does the fact of having a system with a 64-bit CPU (and OS) necessarily (or usually) imply that data transfers between CPU and RAM happen also 64-bit in parallel ? That depends on front bus width. Modern PCs has 64-bit bus AFAIK. In 64-bit CPU 64 is register size and nothing else (although 86x64 mode has some differences with IA32) My understanding is that under a 32-bit platform, each integer will occupy 32 bit, while on a 64-bit platform each will occupy 64 bit (the source program remaining the same). Java integers are always 32bit, are not they? C int may vary from 16 (in BCC 3.1 for DOS) to 64. 64-bit processor mode gives you ability to: 1) address more memory (2^64 bytes theoretically). 2) store more data in register so CPU could now operate 64bit numbers and you need one operation to do something with two 64bit objects opposite to two operations on 32bit. 3) v86 mode is disabled so you can't run 16bit apps :) 4) use new registers, new SSE instructions and so on: http://en.wikipedia.org/wiki/X86-64#Architectural_features - To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org - To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
Re: [OT] Re: Maximum memory that can be assigned to Tomcat on windows platform
On Wed, Nov 30, 2011 at 22:38, André Warnier a...@ice-sa.com wrote: [...] I am not knowledgeable at all in such questions, and while you are at it let me ask a question : Does the fact of having a system with a 64-bit CPU (and OS) necessarily (or usually) imply that data transfers between CPU and RAM happen also 64-bit in parallel ? No, this depends on the bus width, not the address space. And bus widths nowadays are rather in the range of 256/512 bits. For example, let' suppose that I have an application which handles a very large table of integers (the integers themselves being 2exp31), and that periodically all elements of this table have to be updated. My understanding is that under a 32-bit platform, each integer will occupy 32 bit, while on a 64-bit platform each will occupy 64 bit (the source program remaining the same). If there is not a corresponding 64-bit parallel transfer between CPU and memory, then using a 64-bit CPU would be detrimental, no ? Or is this a non-sensical case nowadays ? This depends on the alignment the JVM uses. If it aligns to 8 bytes, then yes, any integer will take up 8 bytes, but so will any byte. In general, the alignment is 4 bytes, except for long values of course. With a 4 byte alignment, this means you can store two ints in a register, and it's then only a matter of logical ands/shifting to obtain the value you want. And these operations are ultra fast ;) -- Francis Galiegue ONE2TEAM Ingénieur système Mob : +33 (0) 683 877 875 Tel : +33 (0) 178 945 552 f...@one2team.com 40 avenue Raymond Poincaré 75116 Paris - To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
