It seems there was some push back due to the complexity and the impact on
the overseer code. So this PR is now probably stale.
I opened a simpler version that introduces a dedicated thread pool for
"expensive" operations. End behavior is the same: we don't execute more
than 5 concurrent expensive
In https://issues.apache.org/jira/browse/SOLR-16879, we have a proposal for
certain core level admin operations to be deemed expensive and throttled
(e.g. only 5 at a time). It only works when invoked with the async style
(with the "async" param).
At present, only BACKUPCORE & RESTORECORE are fla
