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Re^4: Combining Ultra-Dynamic Files to Avoid Clustering (Ideas?)( A DB won't help)

by Your Mother (Archbishop)
on Jul 27, 2004 at 22:09 UTC ( #377873=note: print w/replies, xml ) Need Help??


in reply to Re^3: Combining Ultra-Dynamic Files to Avoid Clustering (Ideas?)( A DB won't help)
in thread Combining Ultra-Dynamic Files to Avoid Clustering (Ideas?)

That's great. You may have already tried this and it might be moot, but does presizing the "array" to 512_000_000 elements help with performance?

  • Comment on Re^4: Combining Ultra-Dynamic Files to Avoid Clustering (Ideas?)( A DB won't help)

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Re^5: Combining Ultra-Dynamic Files to Avoid Clustering (Ideas?)( A DB won't help)
by BrowserUk (Pope) on Jul 27, 2004 at 22:44 UTC

    Firstly, the performance wasn't really the issue at hand. The question was related to disk-storage rather than performance, The reason for highlighting the time taken was to excuse my having based my conclusions upon a miserly 1% of a complete test rather than having sat around for 2 days x N tests :)

    I'm not really sure what you mean by 'array' in the context of using DB_File?

    No array of 512_000_000 elements is ever generated. It's doubtful whether most 32-bit machines could access that much memory.

    The test program just looped 512_000_000 times (or would have if I had let it), and generated a random fileno and data value at each iteration. These are then used to fill in the values of a tied hash that is underlain by a disk-based btree DB file.


    Examine what is said, not who speaks.
    "Efficiency is intelligent laziness." -David Dunham
    "Think for yourself!" - Abigail
    "Memory, processor, disk in that order on the hardware side. Algorithm, algoritm, algorithm on the code side." - tachyon

      I was thinking RECNO, not a BTREE (right?), and you're right, I missed the point :) So the idea is neither relevant nor any good, just a curiosity of whether the following...

      my @h ; tie @h, "DB_File", $filename, O_RDWR|O_CREAT, 0666, $DB_REC +NO; # starting with something like... $h[512_000_000] = "orange";

      would behave like presizing a real array which saves on overhead generated by growing and shrinking it. I just tried a bit of test code and some rather unscientific times of it shows it makes little difference and if it does, it's slightly against the pre-sizing.

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