Elasticsearch DocumentSourceMissingException: Document source missing - Common Causes & Fixes

Brief Explanation

The DocumentSourceMissingException error in Elasticsearch occurs when attempting to retrieve or access the source of a document that doesn't have its source stored or available.

Common Causes

1. The _source field was disabled during indexing.
2. The document was indexed with stored_fields only, without storing the source.
3. The source was removed using the _update_by_query API with "source": "ctx._source = null".
4. Corrupted index or incomplete recovery after a cluster failure.

Troubleshooting and Resolution

1. Check index mapping:

   • Use the GET /{index}/_mapping API to verify if _source is enabled.
   • If disabled, consider reindexing with _source enabled.

2. Verify document existence and stored fields:

   • Use GET /{index}/_doc/{id} to check if the document exists.
   • If it exists, check for stored fields using GET /{index}/_doc/{id}?stored_fields=_source.
   • Note that this is different from DocumentMissingException, which occurs when the document itself doesn't exist

3. Review recent operations:

   • Check if any recent update operations might have removed the source.
   • If so, restore from a backup or reindex from the original data source.

4. Investigate cluster health:

   • Use GET /_cluster/health and GET /_cat/indices?v to check for any index issues.
   • If indices are red or yellow, address underlying cluster problems.

5. Reindex data:

   • If the source is permanently lost, reindex from the original data source.
   • Ensure _source is enabled in the new index mapping.

Best Practices

1. Always enable _source unless you have a compelling reason not to.
2. Regularly backup your Elasticsearch data.
3. Monitor cluster health and address issues promptly.
4. Use version control for index mappings and settings.
5. Implement proper access controls to prevent accidental data modifications.

Frequently Asked Questions

Q: Can I recover the document source if it's missing?
A: If the source was not stored or was deliberately removed, recovery is generally not possible unless you have a backup or can reindex from the original data source.

Q: How can I prevent this error in the future?
A: Ensure that _source is enabled in your index mappings, implement proper access controls, and avoid operations that explicitly remove the source field.

Q: Does this error affect all documents in an index?
A: Not necessarily. It can affect individual documents or a subset of documents, depending on how they were indexed or modified.

Q: Can I still search documents with missing sources?
A: Yes, you can still search these documents, but you won't be able to retrieve their full content in search results.

Q: How does disabling _source affect performance?
A: While disabling _source can save storage space, it limits functionality like reindexing, update operations, and certain types of searches. The performance gain is often outweighed by the loss of flexibility.