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or there's some pretty effective read-ahead action going on with the disk driver

Hm. I used XP personally and professionally for circa 10 years, and I never encountered the situation whereby the first run of a program reading a file wasn't substantially slower than the second run due to cache priming. (Accepting when the file in question was much bigger than the available cache memory, when the second had to re-read the entire file from disk anyway.)

There have been options (FILE_FLAG_RANDOM_ACCESS/FILE_FLAG_SEQUENTIAL_SCAN) in NTFS since its inception designed to give the OS clues as to the best caching strategy to use. But, a) in some fairly extensive testing I performed back in the day on XP, the use of these flags made little or no detectable difference; b) Perl doesn't use them.

And the idea is easily disproved. Download CacheSet; start the program, hit the "Clear" button and confirm.

Then run one of the tests twice in succession. And record the run times. to p the first is substantially slower than the second.


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In reply to Re^11: selecting columns from a tab-separated-values file by BrowserUk
in thread selecting columns from a tab-separated-values file by ibm1620

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