[rrd-users] Sanity checks on Buffer Cache and I/O at peak aggregation times

Tobias Oetiker tobi at oetiker.ch
Tue Sep 27 21:09:58 CEST 2011

Today Rick Jones wrote:

> > the 'problem' is that a disk block which is only hit once a day
> > will most likely not stay in buffer cache, so as rrdtool goes in to
> > update the slow RRAs, it will first have to read the block in order
> > to then update it ...
> It may not be sufficient, but under Linux at least there is the
> posix_fadvise() call - might that enable rrdtool to request the cache to
> retain file sections of particular interest?

rrdtool makes heavy use of fadvise (and madvise) otherwhise buffer
cache use would be seriously poor as linux does excessive
read-a-head ...

> rick jones

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

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