Question #178921 on Graphite changed: https://answers.launchpad.net/graphite/+question/178921
chrismd proposed the following answer: Here's how it works for whisper. When the webapp gets a request to render metric foo, it checks to see if foo exists locally and if it does that's all it uses (plus a cache query but thats not really relevant). If metric foo doesn't exist locally it broadcasts a 'find request' to all webapps in the cluster (the results are memcached). Once it knows which servers have metric foo, it requests the data from one webapp. The webapp cannot effectively collate whisper data from disparate sources because it would have to broadcast every request where one server might have a missing datapoint, it has no way to know if the other servers might have that datapoint. Caching only helps to a point, this would lead to a lot of shared (as opposed to distributed) load. Here's how it works for ceres. When the webapp gets a request to render metric foo, it checks to see what intervals it has datapoints for metric foo for. If it doesn't have all the data locally it broadcasts a find request just as before but the results also include what intervals each server has datapoints for each metric, not just which metrics it has. Whisper doesn't make this data cheaply available, ceres does, and that is really the main difference between the two. -- You received this question notification because you are a member of graphite-dev, which is an answer contact for Graphite. _______________________________________________ Mailing list: https://launchpad.net/~graphite-dev Post to : [email protected] Unsubscribe : https://launchpad.net/~graphite-dev More help : https://help.launchpad.net/ListHelp
