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 flagged as expensive in the PR. I'm thinking other operations should consider such designation too: MERGEINDEXES, SPLIT. That's probably it. Opinions & reviews are welcome as usual! ~ David
