[rrd-developers] rrdcached + collectd issues

kevin brintnall kbrint at rufus.net
Wed Oct 14 04:14:10 CEST 2009

On Mon, Oct 12, 2009 at 11:33:40AM -0700, Thorsten von Eicken wrote:
> Thorsten von Eicken wrote:
> - I'm wondering how we could overcome the RRD working set issue. Even
> with rrdcached and long cache periods (e.g. I use 1 hour) it seems that
> the system comes to a crawl if the RRD working set exceeds memory. One
> idea that came to mind is to use the caching in rrdcached to convert
> the random small writes that are typical for RRDs to more of a
> sequential access pattern. If we could tweak the RRD creation and the
> cache write-back algorithm such that RRDs are always accessed in the
> same order, and we manage to get the RRDs allocated on disk in that
> order, then we could use the cache to essentially do one sweep through
> the disk per cache flush period (e.g. per hour in my case). Of course
> on-demand flushes and other things would interrupt this sweep, but the
> bulk of accesses could end up being more or less sequential. I believe
> that doing the cache write-back in a specific order is not too
> difficult, what I'm not sure of is how to make it such that the RRD
> files get allocated on disk in the that order too. Any thoughts?


Read back about a year in the archives.  Daniel Pocock 
<Daniel.Pocock at barclayscapital.com> started some work on "striping" RRD
files together..  i.e. you would have one large disk file that contained
multiple RRD databases, where the rows were clustered on disk by time..
I'm not sure how far he got on it.

 kevin brintnall =~ /kbrint at rufus.net/

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