Thus spake Jo Rhett (jrh...@netconsonance.com) on Tue, Apr 12, 2011 at 
02:27:23PM -0700:
> From the following page we found some solutions to certain problems we were 
> seeing.  http://net.doit.wisc.edu/~dwcarder/rrdcache/
> 

Hi Jo,

Here are some thoughts:

- My crappy web page more or less evolved into a real paper written by
actual academics which was presented at LISA '07:
http://www.usenix.org/events/lisa07/tech/full_papers/plonka/plonka_html/index.html

- We are now running our (even bigger) MRTG system with (16) solid-state disks 
in a RAID configuration, and needless to say we don't have issues with seek or 
read performance any more.

- Take a look at rrdcached in the 1.4.x branch of code.  I know this doesn't 
help you now, but it is where all of the development effort is going.
While we aren't using this rrdcached yet, we're keeping a close eye on
it as it stabilizes.

- If you could move to a version of rrdtool that at least incorporates the
posix fadvise calls, thay might clear up your issue or go long way towards
resolving it.  This would be version rrdtool-1.2.26 or better.
Presumably you could port that (rather simple) change into the version
that you are running and your OS "does the right thing" with this call.

- As a last resort, you may be able trick your OS to evict pages from the
buffer cache.  See the paper, and this utility:
 http://net.doit.wisc.edu/~plonka/fadvise/

Cheers,
Dale


> This one host is using an older version of RRDtool with little chance for 
> upgrade due to obsolete host OS, so this seemed appealing.  However playing 
> with the module has found it quite immature ... print() statements inside the 
> library, plus a number of fairly obvious bugs due to fixing a specific 
> problem for one application and not for all.
> 
> Issues I've found so far:
> 
>       1. If the application is short lived, tmp files are never renamed and 
> thus never used.  It only works as implemented for long-running applications.
> 
>       2. If the application saves data with "N" for the timestamp, all 
> updates are applied with the same timestamp.
> 
>       3. Not all functions from RRDs.pm implemented
> 
>       4. print() calls in the library routines
> 
>       5. error() function commented out
> 
> I'm sure there are more.  Is anyone else using this in the wild?  Want to 
> collaborate on fixes?
> 
> -- 
> Jo Rhett
> Net Consonance : consonant endings by net philanthropy, open source and other 
> randomness
> 

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