Re^2: Reading huge file content

in reply to Re: Reading huge file content
in thread Reading huge file content

Are you sure?

I'm fairly certain that your physical RAM limits how much you can read into a single memory segment. That is, if you want to read everything into a single variable, you'll need the physical RAM to do it. Virtual memory can only swap out what you aren't currently accessing.

Am I wrong on this?

--
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Comment on Re^2: Reading huge file content

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Re^3: Reading huge file content by GrandFather (Saint) on Dec 06, 2007 at 23:58 UTC
Yes, you are wrong. ;) Approximately: virtual memory systems give a process a chunk of memory that looks to the process like one large contiguous piece of memory. The process can not tell where or how its process space memory is mapped to physical memory. Indeed that mapping may change from access to access. The OS takes care of ensuring that when a process accesses a chunk of process space memory that the access succeeds if possible. That may entail writing a chunk of physical memory to disk, reading another chunk of disk to get the accessed process memory's contents, then fixing up tables to map process memory address to physical addresses. Hitting on the VM doesn't come cheap! Perl is environmentally friendly - it saves trees	[reply]
Re^4: Reading huge file content by BrowserUk (Patriarch) on Dec 07, 2007 at 05:00 UTC
I'd check again. Virtual memory will allow your processes to allocate more memory than you have physical ram, provided that you do not need to process it all as a single contiguous chunk. But the largest single contiguous chunk (eg. string) that you will be able to allocate will always be somewhat less than your total physical ram. Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. "Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."	[reply]
Re^5: Reading huge file content by GrandFather (Saint) on Dec 07, 2007 at 06:53 UTC
Nothing I can find on the web that describes virtual memory systems mentions such a limitation. Almost everything I can find implies that my description of virtual memory is accurate, at least for paged systems (and most of the systems commonly in use are paged). Some of the following links may be of interest: http://www.webopedia.com/TERM/v/virtual_memory.html Virtual_memory http://www.aumha.org/win5/a/xpvm.php http://www.redhat.com/magazine/001nov04/features/vm/ http://lwn.net/Articles/253361/ http://www.cs.gmu.edu/cne/modules/vm/green/defn.html#picture - note second paragraph paging/segmentation Perl is environmentally friendly - it saves trees	[reply]
Re^6: Reading huge file content by BrowserUk (Patriarch) on Dec 07, 2007 at 14:15 UTC
Re^7: Reading huge file content by GrandFather (Saint) on Dec 09, 2007 at 07:54 UTC

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