Is index.merge.scheduler.max_thread_count per node or per index setting?

Elastic Stack Elasticsearch
1

I'm confused by this setting. I used to set this in elasticsearch.yml in v1.7 but now the setting move to index level setting. Does that means:
Per index can have a different value?
Let's say index abc put 1 and index xyz put 2

Any idea? Thanks a lot.

2

Here is my little experiment
Create two indices, abc and test, but put the different settings and then get http://localhost:9200/_settings from Elasticsearch with the following result.
#1. So what is the number that merge scheduler max thread count? 4 or 2 or 4+2?
#2. will merge policy actually different for both index?

{
	"test": {
		"settings": {
			"index": {
				"refresh_interval": "5s",
				"number_of_shards": "1",
				"provided_name": "test",
				"merge": {
					"scheduler": {
						"max_thread_count": "4"
					},
					"policy": {
						"segments_per_tier": "3",
						"max_merge_at_once": "2",
						"max_merged_segment": "10mb"
					}
				},
				"creation_date": "1505384721746",
				"number_of_replicas": "0",
				"uuid": "etDLnuqVSeurnSP25j7CJw",
				"version": {
					"created": "5040099"
				}
			}
		}
	},
	"abc": {
		"settings": {
			"index": {
				"refresh_interval": "5s",
				"number_of_shards": "1",
				"provided_name": "abc",
				"merge": {
					"scheduler": {
						"max_thread_count": "2"
					},
					"policy": {
						"segments_per_tier": "3",
						"max_merge_at_once": "2",
						"max_merged_segment": "10mb"
					}
				},
				"creation_date": "1505402967991",
				"number_of_replicas": "0",
				"uuid": "vvtnZTUMSOabDc-ShdUioA",
				"version": {
					"created": "5040099"
				}
			}
		}
	}
}