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Re^13: selecting columns from a tab-separated-values fileby BrowserUk (Patriarch) |
on Jan 24, 2013 at 23:43 UTC ( [id://1015245]=note: print w/replies, xml ) | Need Help?? |
I'm on CentOS, a Linux disto, not Windows. Sorry. I remembered this reference to XP, but misremembered who made it. I did issue the 'sync' command, but it apparently only commits buffer cache to disk rather than emptying it. A crude but usually effective way of flushing one file from the cache is to cat a file that is bigger than the cache. Say, copy/append your 80GB datafile to another file 5 times (=400GB), and then cat that to /dev/null before running your tests. Might work for you. I'm able to cat my testfile to /dev/null in under one second. Assuming this is your 10e6 record testfile, and it is representative of your 80GB file and has an average of 86 characters/line, that gives a filesize of ~820MB. The very best sequential-read throughput figure I can find for a non-raided 15k local drive is a little over 100MB/s. That pretty much confirms that your testing is reading from cache rather than from disk. Even the most optimistic read-ahead algorithm cannot drive the interface 8 times faster than its maximum throughput. With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
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