Creating a byte[] of long size
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From: Lew on 9 Jul 2010 13:35 Wayne wrote: > 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, who > was one of the lead developers of the FreeBSD kernel. 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. > How big is a page for a Java program? Be sure to account for use on multiple architectures with and without "-XX:LargePageSizeInBytes=??". -- Lew
From: Lew on 9 Jul 2010 13:46 Boris Punk wrote: > Is it not as simple as assigning int as 64 bit and long as 128 bit in newer > versions > That depends. For whom would it be simple, and for whom not? How much legacy code are you willing to break? What about folks who suddenly experience performance degradation because their existing structures suddenly don't fit in on-chip cache any more, whose programs are suddenly twice as large, and for whom memory accesses overall suddenly take twice as long? Whether they need the extra capacity or not? Much safer would be the suggestions upthread of LongCollection classes and perhaps a new "longarray" type. There's no question that larger structures will be needed sometimes, but the need will not be as widespread as some here appear to think. The pressure to have more RAM on a machine, where 640K used to be thought plenty and is now laughably microscopic, had nothing to do with the size of int or much to do with the size of individual data structures, but with the number of distinct structures and logic contained within a program and the number of programs that must run concurrently. Even with the clear need for gigabytes to terabytes of RAM on machines today, pretty much none of that yet is for any building-block data structure to exceed a gigabyte or two. Even today, as pointed out upthread, Java is perfectly capable of handling data structures that exceed 2 GB in size, just not in a single array or int-based structure (or in 32-bit mode). You have to go with multi-dimensional arrays or Collection<Collection> types of structures, but they will work. I predict that even when the need for multi-gigabyte arrays becomes widely acknowledged that the actual use cases for them will remain quite specialized. I venture to say further that the OP doesn't need one yet. -- Lew
From: Tom Anderson on 9 Jul 2010 15:45 On Thu, 8 Jul 2010, Eric Sosman wrote: > Or, you could have BigList implement List but "lie" in its .size() > method, in somewhat the same way TreeSet "lies" about the Set contract. How does TreeSet lie about the Set contract? tom -- The world belongs to the mathematics and engineering. The world is as it is. -- Luis Filipe Silva vs Babelfish
From: Patricia Shanahan on 9 Jul 2010 15:50 On 7/9/2010 12:45 PM, Tom Anderson wrote: > On Thu, 8 Jul 2010, Eric Sosman wrote: > >> Or, you could have BigList implement List but "lie" in its .size() >> method, in somewhat the same way TreeSet "lies" about the Set contract. > > How does TreeSet lie about the Set contract? The case I'm aware of involves a TreeSet with a Comparator, that is not consistent with the .equals methods of the TreeSet elements. The TreeSet always goes by the Comparator results. That means the TreeSet could contain elements a and b such that a.equals(b). Patricia
From: Roedy Green on 9 Jul 2010 19:53
On Thu, 8 Jul 2010 23:22:03 +0100, "Boris Punk" <khgfhf(a)hmjggg.com> wrote, quoted or indirectly quoted someone who said : > >Is there no BigList/BigHash in Java? The tricky thing is, you have no giant arrays to use in implementation. If you want BigHash, I could write you one for a fee. It would use arrays of arrays for addressing inside. -- 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. |