[FEEDBACK] Is this script efficient...is there a better way?
oren-py-l at hishome.net
Thu Sep 12 09:44:00 CEST 2002
On Wed, Sep 11, 2002 at 10:08:35PM -0400, Michael Schneider wrote:
> Bob X wrote:
> >>1) readlines() loads the entire file into a list so if you have a 30+
> >>mb file you just ate 30+mb of memory. Try using xreadlines()
> >>instead, it reads the file line by line and is much more memory
> >Very cool...I had missed that!
> It is much slower though. I am not sure about your config, but I am
> running with a Gig of memory.
> I would much rather have the speed then the 30 mb of memory. Again,
> check your config.
Have you actually tested this? I used to believe that larger buffers are
always better for performance.
I ran some test on Linux for the effect of buffer size on file reading
speed and the results were very interesting. I started with a buffer size
of 32 bytes, tested file I/O throughput and increased it logarithmically by
about 2% for each step. As expected, the time to read 1mb improved as the
buffer size increased until it hit a minimum for a buffer size of around
4-8k (the graph is very noisy so it's hard to tell) and then rose back up
to a value that is 10-20% worse for buffer sizes of 32-64k and remained
more-or-less constant for anything higher.
This performance curve may be a result of the CPU cache or the OS
The chunk size used by xreadlines is 8k which is about the optimum
value (at least for linux).
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