I'm looking for an alternative to the rrdtool
It need to be fast, reliable, able to handle large amounts of data and have a Java interface. One possibilty I'm investigating is KDB+ Any other ideas?
There are two Java ports of RRD: rrd4j and JRobin
If you just want a replacement for RRDTool, K is probably overkill.
JRobin is outdated and no longer developed. RRD4J is the way forward.
Have you looked at RRD4J?
EDIT: RRD4J, which Nat pointed out, is a port of JRobin. At this point, it looks like JRobin is more up to date.