I have a 220GB read-only index (1node, 1 shard and 0 replicas) on ES2.4 running on EC2 (2CPU, 4GB RAM, 50% free SSD, 3GB heap).
Although no queries or indexing are running, I can see almost constant CPU usage around ~25% for the past two hours, during which the cluster/node was effectively idle. htop reports system loads of 0.51, 045 and 0.43 respectively, but iotop reports zero disk usage. It is ES' process that is using CPU, according to htop.
What is keeping my CPU busy? I can't find anything enlightening on hot_threads or _tasks.
GET /hot_threads response:
::: {esnode1}{KNojH4i7QNuY57ILD68cTw}{172.31.11.232}{172.31.11.232:9300}
Hot threads at 2017-06-01T15:58:56.219Z, interval=500ms, busiestThreads=3, ignoreIdleThreads=true:
0.0% (113.1micros out of 500ms) cpu usage by thread 'elasticsearch[esnode1][transport_client_timer][T#1]{Hashed wheel timer #1}'
10/10 snapshots sharing following 5 elements
java.lang.Thread.sleep(Native Method)
org.jboss.netty.util.HashedWheelTimer$Worker.waitForNextTick(HashedWheelTimer.java:445)
org.jboss.netty.util.HashedWheelTimer$Worker.run(HashedWheelTimer.java:364)
org.jboss.netty.util.ThreadRenamingRunnable.run(ThreadRenamingRunnable.java:108)
java.lang.Thread.run(Thread.java:745)
Output from GET /_tasks:
{
"nodes": {
"KNojH4i7QNuY57ILD68cTw": {
"name": "esnode1",
"transport_address": "172.31.11.232:9300",
"host": "172.31.11.232",
"ip": "172.31.11.232:9300",
"tasks": {
"KNojH4i7QNuY57ILD68cTw:4540": {
"node": "KNojH4i7QNuY57ILD68cTw",
"id": 4540,
"type": "transport",
"action": "cluster:monitor/tasks/lists",
"start_time_in_millis": 1496332684463,
"running_time_in_nanos": 91070
},
"KNojH4i7QNuY57ILD68cTw:4541": {
"node": "KNojH4i7QNuY57ILD68cTw",
"id": 4541,
"type": "direct",
"action": "cluster:monitor/tasks/lists[n]",
"start_time_in_millis": 1496332684463,
"running_time_in_nanos": 32876,
"parent_task_id": "KNojH4i7QNuY57ILD68cTw:4540"
}
}
}
}
}
I can't check details about the tasks, as the number after the ":" on the task ID is incremented at every second so every GET _tasks returns different, incremented IDs (i.e. KNojH4i7QNuY57ILD68cTw:4504, KNojH4i7QNuY57ILD68cTw:4508, KNojH4i7QNuY57ILD68cTw:4514, etc)
Thanks