No core value reported for scaling thread pool type

[lukas-vlcek]

Elasticsearch version (bin/elasticsearch --version): >= 5.x

Description of the problem including expected versus actual behavior:

This is probably documentation related issue. There are a few places where the documentation mentions that the scaling thread pool uses the core value for the minimum value. For example:

• Doc for scaling thread pool: "... between the value of the core and max parameters"
• 5.x breaking changes for thread pool settings: "... has been changed from min to core"

However, in the output I see only min value where the core should be expected:

// http://10.8.245.12:9200/_nodes/_local/thread_pool

{
  "_nodes": {
    "total": 1,
    "successful": 1,
    "failed": 0
  },
  "cluster_name": "xxxxxxxx",
  "nodes": {
    "DK0UQ_fFTZ6fz0H2v9XsKw": {
      "name": "xxxxxxxx-1",
      "transport_address": "172.16.220.11:9300",
      "host": "172.16.220.11",
      "ip": "172.16.220.11",
      "version": "5.5.2",
      "build_hash": "b2f0c09",
      "roles": [
        "master",
        "data",
        "ingest"
      ],
      "thread_pool": {
        "force_merge": {
          "type": "fixed",
          "min": 1,
          "max": 1,
          "queue_size": -1
        },
        "fetch_shard_started": {
          "type": "scaling",
          "min": 1,
          "max": 8,
          "keep_alive": "5m",
          "queue_size": -1
        },
        "listener": {
          "type": "fixed",
          "min": 2,
          "max": 2,
          "queue_size": -1
        },
        "index": {
          "type": "fixed",
          "min": 4,
          "max": 4,
          "queue_size": 200
        },
        "refresh": {
          "type": "scaling",
          "min": 1,
          "max": 2,
          "keep_alive": "5m",
          "queue_size": -1
        },
        "generic": {
          "type": "scaling",
          "min": 4,
          "max": 128,
          "keep_alive": "30s",
          "queue_size": -1
        },
        "warmer": {
          "type": "scaling",
          "min": 1,
          "max": 2,
          "keep_alive": "5m",
          "queue_size": -1
        },
        "search": {
          "type": "fixed",
          "min": 7,
          "max": 7,
          "queue_size": 1000
        },
        "flush": {
          "type": "scaling",
          "min": 1,
          "max": 2,
          "keep_alive": "5m",
          "queue_size": -1
        },
        "fetch_shard_store": {
          "type": "scaling",
          "min": 1,
          "max": 8,
          "keep_alive": "5m",
          "queue_size": -1
        },
        "management": {
          "type": "scaling",
          "min": 1,
          "max": 5,
          "keep_alive": "5m",
          "queue_size": -1
        },
        "get": {
          "type": "fixed",
          "min": 4,
          "max": 4,
          "queue_size": 1000
        },
        "bulk": {
          "type": "fixed",
          "min": 4,
          "max": 4,
          "queue_size": 200
        },
        "snapshot": {
          "type": "scaling",
          "min": 1,
          "max": 2,
          "keep_alive": "5m",
          "queue_size": -1
}}}}}

[jasontedor]

We report the same thread pool info for all thread pools. That is, all thread pools, regardless of type, report a min and max (as well as their name and type, and keep_alive and queue_size when applicable) . For a scaling thread pool it is min == core and max == size. For a fixed thread pool it is min == size and max == size.

[lukas-vlcek]

So the thing is that in settings part you say core but what you get back from the API is min. It is confusing but I think I get it now.

[jasontedor]

Yeah, I am sorry for the confusion, it is something that has bothered be that we use this single thread pool info class to represent the underlying information regardless of the thread pool type. I looked into it once before and walked away because I did not see a clean way to refactor this.

[jasontedor]

On second thought, I think we can change this on the display side only without having to endure a wider refactoring.

[elasticmachine]

Pinging @elastic/es-core-infra

[jasontedor]

I opened #29123. Now we get:

{

  "_nodes" : {
    "total" : 1,
    "successful" : 1,
    "failed" : 0
  },
  "cluster_name" : "elasticsearch",
  "nodes" : {
    "TQM_SNpDSsaYROQly2-KgQ" : {
      "name" : "TQM_SNp",
      "transport_address" : "127.0.0.1:9300",
      "host" : "127.0.0.1",
      "ip" : "127.0.0.1",
      "version" : "7.0.0-alpha1",
      "build_hash" : "2f21dc7",
      "roles" : [
        "master",
        "data",
        "ingest"
      ],
      "thread_pool" : {
        "force_merge" : {
          "type" : "fixed",
          "size" : 1,
          "queue_size" : -1
        },
        "fetch_shard_started" : {
          "type" : "scaling",
          "core" : 1,
          "max" : 16,
          "keep_alive" : "5m",
          "queue_size" : -1
        },
        "listener" : {
          "type" : "fixed",
          "size" : 4,
          "queue_size" : -1
        },
        "index" : {
          "type" : "fixed",
          "size" : 8,
          "queue_size" : 200
        },
        "refresh" : {
          "type" : "scaling",
          "core" : 1,
          "max" : 4,
          "keep_alive" : "5m",
          "queue_size" : -1
        },
        "generic" : {
          "type" : "scaling",
          "core" : 4,
          "max" : 128,
          "keep_alive" : "30s",
          "queue_size" : -1
        },
        "warmer" : {
          "type" : "scaling",
          "core" : 1,
          "max" : 4,
          "keep_alive" : "5m",
          "queue_size" : -1
        },
        "search" : {
          "type" : "fixed_auto_queue_size",
          "size" : 13,
          "queue_size" : 1000
        },
        "flush" : {
          "type" : "scaling",
          "core" : 1,
          "max" : 4,
          "keep_alive" : "5m",
          "queue_size" : -1
        },
        "fetch_shard_store" : {
          "type" : "scaling",
          "core" : 1,
          "max" : 16,
          "keep_alive" : "5m",
          "queue_size" : -1
        },
        "management" : {
          "type" : "scaling",
          "core" : 1,
          "max" : 5,
          "keep_alive" : "5m",
          "queue_size" : -1
        },
        "get" : {
          "type" : "fixed",
          "size" : 8,
          "queue_size" : 1000
        },
        "bulk" : {
          "type" : "fixed",
          "size" : 8,
          "queue_size" : 200
        },
        "snapshot" : {
          "type" : "scaling",
          "core" : 1,
          "max" : 4,
          "keep_alive" : "5m",
          "queue_size" : -1
        }
      }
    }
  }
}