Does having too many metrics hurt query or write speed?

[John Humphreys]

Having more metrics and less tags (e.g. pushing host to metric) supposedly improves query performance.

This may result in may more metrics though, requiring more UIDs.

As an example; would having 15 million metrics make OpenTSDB slower because it can't cache all their UIDs in memory at once?

[ManOLamancha]

It depends on the size of the TSD JVM, so you may need more heap space there. We're trying out an LRU in 2.4 but with a multi-gig JVM heap you should be able to have millions of entries without a problem.