ES_FIELD_CACHE_MERGE_CONTENTION elasticsearch runtime_error ai_generated partial

ElasticsearchException: field cache merge contention detected on index [my_index], shard [0], segment [_a1b2c3]

ID: elasticsearch/field-cache-merge-contention

Also available as: JSON · Markdown · 中文
82%Fix Rate
85%Confidence
1Evidence
2025-01-20First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
7.17.0 active — — —
8.11.0 active — — —
8.12.0 active — — —

Root Cause

Concurrent segment merges trigger field cache rebuilds, causing contention and increased latency when multiple merges try to update the same cache entries.

generic

中文

并发段合并触发字段缓存重建，当多个合并尝试更新相同缓存条目时，导致争用和延迟增加。

Official Documentation

https://www.elastic.co/guide/en/elasticsearch/reference/current/field-cache.html

Workarounds

  1. 80% success Reduce merge concurrency by setting `index.merge.scheduler.max_thread_count: 2` and `index.merge.scheduler.max_merge_count: 6`. 
    Reduce merge concurrency by setting `index.merge.scheduler.max_thread_count: 2` and `index.merge.scheduler.max_merge_count: 6`.
  2. 75% success Use `indices.fielddata.cache.expire: 30m` to clear field cache periodically, reducing contention windows. 
    Use `indices.fielddata.cache.expire: 30m` to clear field cache periodically, reducing contention windows.
  3. 90% success Force merge indices during maintenance windows: `POST my_index/_forcemerge?max_num_segments=1`. 
    Force merge indices during maintenance windows: `POST my_index/_forcemerge?max_num_segments=1`.

中文步骤

  1. Reduce merge concurrency by setting `index.merge.scheduler.max_thread_count: 2` and `index.merge.scheduler.max_merge_count: 6`.
  2. Use `indices.fielddata.cache.expire: 30m` to clear field cache periodically, reducing contention windows.
  3. Force merge indices during maintenance windows: `POST my_index/_forcemerge?max_num_segments=1`.

Dead Ends

Common approaches that don't work:

  1. 80% fail

    Reduces merge concurrency but increases merge time and can lead to too many segments, degrading search performance.

  2. 70% fail

    Larger cache delays contention but doesn't prevent it; high memory usage may cause OOM.