[rrd-developers] rrd cache work

[Tobias Oetiker]

Hi Scott,

> In our experience on linux centos 4 and 5, rrdtool performance
> problems seem primarily related to the rate at which the os flushes
> the rrd updated pages in the filesystem cache to disk.  Not so much to
> the actual rate that the rrd_update function is called.
>
> There is a tip on the rrdtool web site under VM optimizations,
>
>   By setting dirty_expire_centisecs to a high value (several steps),
>   while all rrd data fits into the cache, will cause your system to
>   bundle up several rounds of updates before writing the dirty buffers
>   back to disk.
>
>   http://oss.oetiker.ch/rrdtool-trac/wiki/TuningRRD
>
> Wondering if any thought has been given to addressing the update
> bottleneck problem at a lower level?

in 1.3 we did address the problem of cache pollution by giving
advice about the planned usage patterns to the OS. We also file
access over to mmapedio. Apart from this I think the OS is the
right place to optimize disk access.

So as long as the rrdtool database format remains column oriented I
don't see what optimization is left on that front ...

cheers
tobi



-- 
Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten, Switzerland
http://it.oetiker.ch tobi at oetiker.ch ++41 62 775 9902 / sb: -9900