[es] Hot Threads API

Elasticsearch의 hot_threads API는 클러스터 내에서 CPU가 높게 사용되는 스레드 정보를 제공하는 엔드포인트입니다. 이를 통해 어떤 작업이 CPU를 많이 사용하고 있는지를 식별하고 성능 이슈를 해결할 수 있음

 

 

Hot Threads API 사용 방법:

cURL을 사용한 기본 사용법

curl -X GET "localhost:9200/_nodes/hot_threads?pretty"

위 명령은 로컬 호스트의 9200번 포트에서 실행 중인 Elasticsearch에 연결하고, 각 노드의 hot threads 정보를 출력.

 

 

위 명령은 각 노드에서 상위 5개의 hot threads만 출력합니다. threads 파라미터를 사용하여 출력할 스레드의 수를 조절할 수 있음

curl -X GET "localhost:9200/_nodes/hot_threads?threads=5&pretty"

 

함 해보자

GET _nodes/node-prd-totalsearch-01-data/hot_threads?pretty
GET _nodes/node-prd-totalsearch-02-data/hot_threads?pretty
GET _nodes/node-prd-totalsearch-03-data/hot_threads?pretty
GET _nodes/node-prd-totalsearch-04-data/hot_threads?pretty
GET _nodes/node-prd-totalsearch-05-data/hot_threads?pretty
GET _nodes/node-prd-totalsearch-06-data/hot_threads?pretty

 

 

Hot Threads API 출력 예시:

Hot Threads API의 출력은 다음과 비슷한 형태를 가질 수 있습니다:

 

::: {node_name}{node_id} 
   Hot threads at 2022-01-01T00:00:00Z, ...

각 노드의 hot threads는 해당 노드의 이름과 ID로 시작합니다. 그 후, 각 스레드에 대한 정보가 표시됩니다.

 

 

   1.0% (4ms out of 500ms) cpu usage by thread 'elasticsearch[...][[search][[example-index][2]:]'
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       app//org.apache.lucene.util.packed.AbstractBlockPackedReader.readValues(AbstractBlockPackedReader.java:266)
       app//org.apache.lucene.search.DocIdSetBuilder$BulkBuffer.add(DocIdSetBuilder.java:235)
       app//org.apache.lucene.search.DocIdSetBuilder$Bulk.add(DocIdSetBuilder.java:276)
   0.0% (0s out of 500ms) cpu usage by thread 'elasticsearch[...][[search][[example-index][0]:]'
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       app//org.apache.lucene.util.packed.MonotonicBlockPackedReader.fillBulk(MonotonicBlockPackedReader.java:77)
       app//org.apache.lucene.util.packed.AbstractBlockPackedReader.readValues(AbstractBlockPackedReader.java:266)
       app//org.apache.lucene.search.DocIdSetBuilder$BulkBuffer.add(DocIdSetBuilder.java:235)
       app//org.apache.lucene.search.DocIdSetBuilder$Bulk.add(DocIdSetBuilder.java:276)
       app//org.elasticsearch.search.aggregations.bucket.terms.PrefixFieldMapper$PrefixFieldData.build(FixedBitSet.java:813)

 

출력 내용의 해석:

• 각 스레드의 CPU 사용량 및 작업 정보가 표시됩니다.
• cpu usage by thread 부분에서는 각 스레드의 CPU 사용량이 얼마나 되는지가 나타납니다.
• Thread의 이름이나 식별자, 해당 스레드가 어떤 작업을 수행 중인지 등의 정보가 표시됩니다.
• 각 스레드의 스택 트레이스를 통해 스레드가 어떤 메서드에서 시간을 소비하는지 확인할 수 있습니다.

Hot Threads API를 사용하면 Elasticsearch 클러스터에서 가장 CPU가 많이 사용되는 스레드를 식별하고, 성능 이슈를 파악하는 데 도움이 됩니다.

 

 

   87.0% (434.8ms out of 500ms) cpu usage by thread 'elasticsearch[node-prd-totalsearch-04-data][write][T#6]'
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       java.base@11.0.8/java.lang.Thread.run(Thread.java:834)

 

 

 

81.7% (408.3ms out of 500ms) cpu usage by thread 'elasticsearch[node-prd-totalsearch-04-data][write][T#7]'
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