Creating a byte[] of long size
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From: Roedy Green on 9 Jul 2010 19:56 On Fri, 09 Jul 2010 08:49:27 -0400, Eric Sosman <esosman(a)ieee-dot-org.invalid> wrote, quoted or indirectly quoted someone who said : >> Arrays can only be indexed by ints, not longs. Even if they were, >> even Bill Gates could not afford enough RAM for an array of bytes, one >> for each possible long. > > True, but not especially relevant: You'll hit the int limit long >before running out of dollars. $50US will buy more RAM than a Java >byte[] can use. I don't think our two posts conflict. -- Roedy Green Canadian Mind Products http://mindprod.com You encapsulate not just to save typing, but more importantly, to make it easy and safe to change the code later, since you then need change the logic in only one place. Without it, you might fail to change the logic in all the places it occurs.
From: Arne Vajhøj on 9 Jul 2010 20:21 On 09-07-2010 02:07, Mike Schilling wrote: > "Arne Vajh�j" <arne(a)vajhoej.dk> wrote in message > news:4c366580$0$280$14726298(a)news.sunsite.dk... >> On 08-07-2010 17:15, Lew wrote: >>> From the JLS, which I strongly urge you to study: >> >> Unless the poster has a solid programming experience, >> then the JLS may not be the best to study. >> >> Sure it is by definition correct, > > mod typos and misstatements, of course. What counts: "what is written in the spec" or "what should have been written in the spec" ? Arne
From: Arne Vajhøj on 9 Jul 2010 20:23 On 08-07-2010 22:40, Wayne wrote: > On 7/8/2010 5:35 PM, Boris Punk wrote: >> Integer.MAX_VALUE = 2147483647 >> >> I might need more items than that. I probably won't, but it's nice to have >> extensibility. > > To me, it is unlikely your system will run well if this one data structure > consumes 2G of memory. (You didn't really state the application or system; > certainly there are exceptions to the rule.) I would suggest you use a > more flexible system, where you keep the data on storage (disk) and use > memory as a cache. Perhaps an ArrayList of soft references would work well. > It might even be possible in your particular case to run a daemon thread > that pre-fetches items into the cache. You mean reinvent what the virtual memory system is already providing for free? > Keep in mind a modern general-purpose computer will use virtual memory, > typically with 4kiB pages. Any data structure larger than that will > likely end up swapped to disk anyway. Absolutely not. Lots of systems does not page much even with huge data. Arne
From: Arne Vajhøj on 9 Jul 2010 20:38 On 09-07-2010 12:21, Wayne wrote: > On 7/9/2010 12:31 AM, Patricia Shanahan wrote: >> Wayne wrote: >>> On 7/8/2010 5:35 PM, Boris Punk wrote: >>>> Integer.MAX_VALUE = 2147483647 >>>> >>>> I might need more items than that. I probably won't, but it's nice to have >>>> extensibility. >>> >>> To me, it is unlikely your system will run well if this one data structure >>> consumes 2G of memory. (You didn't really state the application or system; >>> certainly there are exceptions to the rule.) I would suggest you use a >>> more flexible system, where you keep the data on storage (disk) and use >>> memory as a cache. Perhaps an ArrayList of soft references would work well. >>> It might even be possible in your particular case to run a daemon thread >>> that pre-fetches items into the cache. >> >> What's the difference between one data structure occupying over 2 GB and a set of >> data structures that use that much space? >> >> Certainly, given enough memory, Java can support total data structure sizes well over >> 2 GB without excessive paging. > > A reduction in the number of page faults. There was an interesting article about > this topic in this month's Communications of the ACM, by Poul-Jenning Kamp, Poul-Henning Kamp often abbreviated PHK. > who > was one of the lead developers of the FreeBSD kernel. He still contributes to FreeBSD. > He applied his insight > to a web proxy replacement for Squid called Varnish, and was able to replace > 12 Squid machines with 3 Varnish ones. It used a modified binary heap he called > a B-heap, which respected the page size of memory. The article was titled > "You're doing It Wrong". The message I came away with was, don't ignore the > fact that computers use paging when designing large data structures. I was > thinking that lesson might apply to the OP's situation. I assume you are talking about this article: http://queue.acm.org/detail.cfm?id=1814327 He is not suggesting any custom swap to disk or anything, but just noting that it is beneficial to keep stuff together to minimize paging. In what may actually be an earlier version of the same story: http://www.version2.dk/artikel/13201-poul-henning-kamp-ungdommen-kan-ikke-programmere-til-et-moderne-os translated: http://translate.google.com/translate?js=y&prev=_t&hl=en&ie=UTF-8&layout=1&eotf=1&u=http%3A%2F%2Fwww.version2.dk%2Fartikel%2F13201-poul-henning-kamp-ungdommen-kan-ikke-programmere-til-et-moderne-os&sl=da&tl=en he explicit states: 'A classic example is that you stand and move things between disk and memory at all times. Men det g�r operativsystemkernen jo selv. But it makes the operating system kernel yourself. Man skal bare l�gge det et sted i den virtuelle hukommelse, s� g�r den det selv, og det er den meget bedre til. You just put it somewhere in the virtual memory, so it makes it even and it is much better. Men det er folk ikke klar over,� lyder vurderingen fra Poul-Henning Kamp. But people are not aware, "reads the assessment from Poul-Henning Kamp. Arne
From: Arne Vajhøj on 9 Jul 2010 20:42
On 09-07-2010 13:24, Boris Punk wrote: > "Kevin McMurtrie"<mcmurtrie(a)pixelmemory.us> wrote in message >> 24GB of RAM is a standard server configuration this year. Even my >> laptop has 8GB and can only run 64 bit Java. A Java array indexing >> limit of 2147483647 is a growing problem, not a future problem. > Is it not as simple as assigning int as 64 bit and long as 128 bit in newer > versions? No. Lots of code would break. Code that relies on overflow. Code that relies on bit masks. Arne |