Opster Team
Last updated: Jan 6, 2023
| 1 min readIn addition to reading this guide, we recommend you run the Elasticsearch Health Check-Up. It will detect issues and improve your Elasticsearch performance by analyzing your shard sizes, threadpools, memory, snapshots, disk watermarks and more.The Elasticsearch Check-Up is free and requires no installation.
Aside from reading about Elasticsearch _source and reviewing the various use cases, we recommend you run the Elasticsearch Health Check-Up. It will detect issues and improve your Elasticsearch performance by analyzing your shard sizes, threadpools, memory, snapshots, disk watermarks and more.
The Elasticsearch Check-Up is free and requires no installation.
Overview
When a document is sent for indexing, Elasticsearch indexes all the fields in the format of an inverted index, but it also keeps the original JSON document in a special field called _source.
Examples
Disabling source field in the index:
PUT /api-logs?pretty { "mappings": { "_source": { "enabled": false } } }
Store only selected fields as a part of _source field:
PUT api-logs { "mappings": { "_source": { "includes": [ "*.count", "error_info.*" ], "excludes": [ "error_info.traceback_message" ] } } }
Including only selected fields using source filtering:
GET api-logs/_search { "query": { "match_all": {} }, "_source": { "includes": ["api_name","status_code", "*id"] } }
Notes
The source field brings an overhead of extra storage space but serves special purposes such as:
- Return as a part of the response when a search query is executed.
- Used for reindexing purpose, update and update_by_query operations.
- Used for highlighting, if the field is not stored, it means the field is not set as “store to true” inside the mapping.
- Allows selection of fields to be returned.
The only concern with source field is the extra storage usage on disk. But this storage space used by source field can be optimized by changing compression level to best_compression. This setting is done using index.codec parameter.
Related log errors to this ES concept
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