Persistent Reindex Failure from Source-Only Snapshot: unexpected docvalues type NONE for field '_ignored' error

Elastic Stack Elasticsearch
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Hello,

I am attempting to restore a data stream from a source-only snapshot and then reindex it into a new, functional data stream, as required by the source-only documentation.

The restore operation completes successfully, resulting in a read-only index. However, the subsequent _reindex operation consistently fails with the following error:

unexpected docvalues type NONE for field '_ignored' (expected one of [SORTED, SORTED_SET]). Re-index with correct docvalues type.

This error suggests a mismatch in the doc_values expectation for the internal _ignored metadata field between the source (which has NONE due to the source-only nature) and the destination (which expects SORTED or SORTED_SET).

Environment Details

  • Elasticsearch Version: 8.18.2

Steps Taken So Far

I have attempted several workarounds based on common advice for similar reindexing errors, but the error persists:

  1. Verified Source Mapping: I checked the mapping of the restored source index (GET <restored-index>/_mapping). The _ignored field is not present in the explicit mapping, as it's an internal metadata field.

  2. Used Ingest Pipeline to Remove Field: I created and used an ingest pipeline with a remove processor for the _ignored field, but the error still occurred.

  3. Created Destination Index with Explicit Mapping & Template: I manually created the destination index with a high-priority index template that explicitly set "doc_values": false for the _ignored field before running the reindex. Even with this, the error persists.

Has anyone successfully worked around this specific _ignored field conflict when reindexing from a source-only snapshot?

It seems that the destination index, even with explicit template overrides or source exclusions, is still trying to force a doc_values type on this internal field that the source-only data simply doesn't support.

Is there an internal cluster setting or a different, supported method to handle metadata fields like _ignored during a reindex from a source-only restore?

Any insight or a reliable fix would be appreciated