Add admin API to kill running queries

[pjeli]

Seen instances where an NNA instance can get locked up from running expensive queries. Would be nice to interrupt the requests and get back to stable state.

This issue is to try to make that possible.

[pjeli]

So there isn't exactly an easy way to stop queries but we can put in a safe guard that will only let the current running query finish and then cancel all others after. That should work for now. Otherwise we'd have to shut down the ForkJoinPool and then restore it somehow - seems too catastrophic for the application.

[pjeli]

Just some confirmation on how this works. There is now a /queryGuard endpoint. When you hit the endpoint with an HTTP GET call you will either enter the guard mode or drop it.

You can always check /info to see if you are guarding or not.

If you are in guard mode, then no other queries except the one that is currently running (prior to entering guard mode) will run. Anything queue'd up will fail instantly with an Exception saying "Query cancelled.".

If you are not in guard mode then all queries will continue to process in NNA as usual.

Guard mode does not stop the SuggestionsEngine - it will continue to process in the background as usual.