Each time RRDTool updates, it will update all the points in the RRAs that have 
completed since the previous update.

If you have left it a long time since the last update, and you have a large 
number of RRAs, then there are potentially a very large number of updates 
pending, as all the missed updates need to be set to 'unknown'.  This will take 
much more time than a normal update.  Even though the gap is being filled with 
NaN (unknown) it still needs to be calculated, the rollup RRAs calculated 
(based on the XFF settings, etc).

There is no easy way around this;  RRDTool optimises its work by spreading the 
consolidation work over the chain of updates, so a large missed gap will be 
more expensive, computationally.  You may save time by placing rrdcached in 
between the updates and the RRD files; if nothing else, you can certainly have 
the update call return quickly.

Steve Shipway

University of Auckland ITS
UNIX Systems Design Lead
[email protected]
Ph: +64 9 373 7599 ext 86487


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