We know that all the indices, types,etc are stored as lucene indices in segments. The data in /var/lib/elasticsearch/<cluster_name>/nodes/0/indices/<index_ name>/0/index has files with .cfs , .cfe, .pos, .tim, etc extensions for each segment. I want to find out the number of lucene indices in each segment. Can this be used for performance tuning of the cluster?
One shard = one Lucene index.
Yes, you can reduce the number of segment by the force_merge operation to improve search performance https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-forcemerge.html
The operation is very expensive and should not be run too frequently.
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