2007-10-22
The dangerous appeal of the obvious
For reasons that do not fit into the margins of this entry, DWiki
sometimes needs to get the current Unix load average. I developed DWiki
on Linux, and getting the load average on Linux is really easy; you read
a line from /proc/loadavg, split it into three floating point numbers,
and you're done. So I wrote a get_load function that did that and
forgot about the whole thing.
Then this server got changed from Linux to FreeBSD, and suddenly that code didn't work any more. (Because I had been paranoid, it didn't fail explosively; I had assumed that someday system problems might cause things to fail and coped with it.)
FreeBSD doesn't have a /proc/loadavg; instead it has a getloadavg(3)
function in the C library. I gloomily contemplated how to make a C
library call from Python, and on the off chance someone had already
written an extension module to do it I did a Google search on [python
getloadavg].
Which promptly turned up the general and supported
Python function to do just this, os.getloadavg(). This not only
solved my problem but would have saved me the effort of writing
my get_load function in the first place, if only I had thought
to look for it instead of leaping on the obvious way of getting the
load average on Linux that I already knew about.
This is the dangerous appeal of the obvious: just because I know how to do something doesn't mean that I know the best way to do something. Maybe I should keep looking slightly harder, just to make sure.
(You could say my issue with rounding up was the same effect in action, although it was less obvious to me then.)