Re: Tie::File surprise (to me)
- From: boyd <tbmoore9@xxxxxxxxxxx>
- Date: Tue, 27 Mar 2007 18:21:45 GMT
In article <tbmoore9-CE1501.13303327032007@xxxxxxxxxxxxxxxx>,
boyd <tbmoore9@xxxxxxxxxxx> wrote:
I probably should have known this, but didn't. In Tie::File, where you
tie an array to a long file, and you want to read backwards from the end
of it ( to look for the most recent lines, for example, in a log file),
it is much faster to address the lines with $index as a negative number,
meaning to search from the end of the array. It takes a while for the
module to find the index = -1, but the subsequent searches on -2, -3,
etc. are much faster than using @#array-1, @#array-2, etc.
This may be optimized in later versions - I am using 0.97 version of
Tie::File.
The times I got were on a log file of 30000 lines or so: (my target
lines were ones that started with /^From: / )
Finding last line index, the first way, took: 1.21123 seconds
Finding the "from" lines, the first way, took: 1.86017 seconds
Finding last line index, the second way, took: 1.01147 seconds
Finding the "from" lines, the second way, took: 0.0000119 seconds
where "first way" is using @#array value and decrementing it,
the "second way" is using -1, -2, ...
Finding the last line is about the same in both cases (varies from run
to run) (I used Time::HiRes to get the times - not as accurate as
Devel::DProf, but easier to use in my script).
But notice the tremendous difference in the time of finding the "from"
lines.
Comments?
Boyd
Ignore this posting - I made a dumb error in my second loop - it was not
really running at all. :-!
Boyd
.
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