Hot shard identification

Hot shard identification root cause analysis (RCA) lets you identify a hot shard within an index. A hot shard is an outlier that consumes more resources than other shards and may lead to poor indexing and search performance. The hot shard identification RCA monitors the following metrics:

CPU utilization
Heap allocation rate

Shards may become hot because of the nature of your workload. When you use a _routing parameter or a custom document ID, a specific shard or several shards within the cluster receive frequent updates, consuming more CPU and heap resources than other shards.

The hot shard identification RCA compares the CPU utilization and heap allocation rates against their threshold values. If the usage for either metric is greater than the threshold, the shard is considered to be hot.

For more information about the hot shard identification RCA implementation, see Hot Shard RCA.

Example request

The following query requests hot shard identification:

GET _plugins/_performanceanalyzer/rca?name=HotShardClusterRca

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Example Response

The response contains a list of unhealthy shards:

"HotShardClusterRca": [{
  "rca_name": "HotShardClusterRca",
  "timestamp": 1680721367563,
  "state": "unhealthy",
  "HotClusterSummary": [
    {
      "number_of_nodes": 3,
      "number_of_unhealthy_nodes": 1,
      "HotNodeSummary": [
        {
          "node_id": "7kosAbpASsqBoHmHkVXxmw",
          "host_address": "192.168.80.4",
          "HotResourceSummary": [
            {
              "resource_type": "cpu usage",
              "resource_metric": "cpu usage(num of cores)",
              "threshold": 0.027397981341796683,
              "value": 0.034449630200405396,
              "time_period_seconds": 60,
              "meta_data": "ssZw1WRUSHS5DZCW73BOJQ index9 4"
            },
            {
              "resource_type": "heap",
              "resource_metric": "heap alloc rate(heap alloc rate in bytes per second)",
              "threshold": 7605441.367010161,
              "value": 10872119.748328414,
              "time_period_seconds": 60,
              "meta_data": "ssZw1WRUSHS5DZCW73BOJQ index9 4"
            },
            {
              "resource_type": "heap",
              "resource_metric": "heap alloc rate(heap alloc rate in bytes per second)",
              "threshold": 7605441.367010161,
              "value": 8019622.354388569,
              "time_period_seconds": 60,
              "meta_data": "QRF4rBM7SNCDr1g3KU6HyA index9 0"
            }
          ]
        }
      ]
    }
  ]
}]

Response fields

The following table lists the response fields.

Field	Type	Description
rca_name	String	The name of the RCA. In this case, “HotShardClusterRca”.
timestamp	Integer	The timestamp of the RCA.
state	Object	The state of the cluster determined by the RCA. The `state` can be `healthy`, `unhealthy`, or `unknown`.
HotClusterSummary.HotNodeSummary.number_of_nodes	Integer	The number of nodes in the cluster.
HotClusterSummary.HotNodeSummary.number_of_unhealthy_nodes	Integer	The number of nodes found to be in an `unhealthy` state.
HotClusterSummary.HotNodeSummary.HotResourceSummary.resource_type	Object	The type of resource causing the unhealthy state, either “cpu usage” or “heap”.
HotClusterSummary.HotNodeSummary.HotResourceSummary.resource_metric	String	The definition of the resource_type. Either “cpu usage(num of cores)” or “heap alloc rate(heap alloc rate in bytes per second)”.
HotClusterSummary.HotNodeSummary.HotResourceSummary.threshold	Float	The value that determines whether a resource is contended.
HotClusterSummary.HotNodeSummary.HotResourceSummary.value	Float	The current value of the resource.
HotClusterSummary.HotNodeSummary.HotResourceSummary.time_period_seconds	Time	The amount of time that a shard was monitored before its state was declared to be healthy or unhealthy.
HotClusterSummary.HotNodeSummary.HotResourceSummary.meta_data	String	The metadata associated with the resource_type.

In the preceding example response, meta_data is QRF4rBM7SNCDr1g3KU6HyA index9 0. The meta_data string consists of three fields:

Node name: QRF4rBM7SNCDr1g3KU6HyA
Index name: index9
Shard ID: 0

This means that shard 0 of index index9 on node QRF4rBM7SNCDr1g3KU6HyA is hot.