Elasticsearch Source



Elasticsearch Source

Opster Team

July 2020, Version: 1.7-7.9


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Source in Elasticsearch

What it is:

When a document is sent to for indexing, Elasticsearch indexes all the fields in the format of 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


Could not update watcher stopped status to ; source
Failed to acquire searcher; source
Giving up on search because it failed with a non-retryable exception
Failed to clear scroll
Snapshot differs from actual index for file: meta:
Remote file corruption on node ; recovering . local checksum OK
Releasing snapshot caused exception
Failed to shutdown the remote connection
Corrupted file detected checksum mismatch
Giving up on search because it failed with a non-retryable exception
Close engine failed
Failed to send error back to recovery source

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