[ccache] explanation of ccache stats

St├ęphane Charette stephanecharette at gmail.com
Thu Mar 17 20:29:41 UTC 2016


>
>
> Hmm, I looked at the code a bit and I don't think this will fly:
>
> find /home -maxdepth 3 -type f -name ccache.conf | sort
>
>
This started out as a plugin just for myself.  I needed to come up with a
way to find the ccache directory without hard-coding my username into the
plugin.

If there is a better way for root to find all the ccache directories
without hard-coding a value, please let me know!  This was the best I could
come up with.


In an enterprise setting, this will cause a lot of thrashing
> only to come up with nothing since ccache isn't stored there.
>


Correct, if the ccache directories are not stored in the user's home
directories, then that line would have to be changed.  I guess this limits
the plugin to people like myself using ccache on a system with "normal"
configuration.


> This is reasonable, but misses those things not being reported:
>
> ccache_total=$((ccache_hit + ccache_miss))
>
> That is, if ccache fails for some other reason you won't see it.
>


Correct, I was just curious to see how "effective" ccache was in my
projects, in terms of hits versus misses.  (I'm averaging 75%.)  Also note
that the only stats I know about (since I've never dug into the ccache
source code) is the output of ccache --show-stats.  Are there other stats
not reported in --show-stats?  If so, where are they stored?

Otherwise, it is looking good! Especially like the "effectiveness".
> Not sure if 1-min or 5-min is best, guess it depends on volume...
>

Munin runs every 5 minutes.  That I don't get to define.  But unless the
ccache stats are being reset back down to zero more often than once every 5
minutes, this shouldn't be a problem.  (
http://munin-monitoring.org/wiki/faq#Q:CanIrunmuninatdifferenttimeintervalsthanthedefault
)

St├ęphane


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