[rrd-developers] rfc: later caching

Thorsten von Eicken tve at voneicken.com
Fri Apr 17 08:45:10 CEST 2009

Tobias Oetiker wrote:

Interesting ideas. But I'm a bit confused... First you say
> The question was, why we were caching at the 'input' stage
> and not at the output stage, since the writing to disk is what is
> hurting us ...
but then you say
> * the (big) disadvantage is that updatev does not work anymore, and
>   for larger deployments updatev is a cornerstone function in
>   driving holt winters based alerting.
I understand the holt-winters issue, but what is the issue around "since 
the writing to disk is what is hurting us"? I.e. is the only benefit of 
caching at the output stage that holt-winters can be made to work? 
Furthermore, how would caching at the output stage differ from the OS 
disk cache? I'm running cached's with a 1-hour cache, which is 40% of 
the first-level RRA, would I see a 2x improvement in cache capacity?


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