Explore using mmap for data file access

[Michael Leinartas]

From question: https://answers.launchpad.net/graphite/+question/191807

Original description:

I read in one of the answers (comment #4 in https://answers.launchpad.net/graphite/+question/170794) that carbon-cache keeps writing to both the first and last blocks of each .wsp file.
This means that it has to keep doing lseek+read+write system calls every time it updates the file.
I'm not very familiar with Python but a quick search tells me that it supports mmap (http://docs.python.org/library/mmap.html).
Using mmap(2) could give a huge advantage:
1. No system calls (which are expensive).
2. No copying of data between the process user-space and kernel buffers on each read/write

[Michael Leinartas (mleinartas)]

Migrated to Github: https://github.com/graphite-project/whisper/issues/20