Thanks, that makes sense.
Now I just really would like to see how this changes over time.
Sadly, monitoring the JVM heap won't show anything due to GCs and all stuff happening there, it's just a wildly changing graph.
It's very bad that I don't know how much memory is used by keeping those scrolls and in either versions (6.x where somebody will get an OOM and in 7.x where queries will be just rejected, if I understand it right) there is no way to measure this.
I think even an approximation would be good here for a start, if the CoW semantics make this hard to do exact measures.
May we have such a stat?
For other stuff elastic gives a pretty fine way to figure out what happens to help debugging problems, but this seems to me a black box (no way to see detailed info about open scrolls, no way to see how much memory they hold etc).