[rrd-users] slow update after pause

[Steve Shipway]

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
s.shipway at auckland.ac.nz
Ph: +64 9 373 7599 ext 86487