Major Description
When changing a collection configuration or schema there may be non-obvious conflicts between existing data and the new configuration or the newly declared schema. A similar situation arises when upgrading Solr to a new version while keeping the existing data.
Currently the SegmentsInfoRequestHandler provides insufficient information to detect such conflicts. Also, there's no collection-wide command to gather such status from all shard leaders.
This issue proposes extending the /admin/segments handler to provide more low-level Lucene details about the segments, including potential conflicts between existing segments' data and the current declared schema. It also adds a new COLSTATUS collection command to report an aggregated status from all shards, and optionally for all collections.