What are the three NiFi repositories and what does each store?

Apache NiFi uses three on-disk repositories, each serving a distinct durability and query purpose.

FlowFile Repository: Stores the current state of all active FlowFiles — their attributes and a pointer (content claim) to where content lives in the content repository. Uses a Write-Ahead Log (WAL) for durability. On restart after a crash NiFi replays the WAL to recover all in-flight FlowFiles without data loss. Stores metadata only, not content bytes.

Content Repository: Stores actual FlowFile payload bytes organized into content claims within large archive files. Uses an immutable, append-only approach: processors write new content versions rather than overwriting. Old claims are garbage-collected once dereferenced. Can be spread across multiple disk volumes for higher I/O throughput.

Provenance Repository: Records every lifecycle event for every FlowFile: RECEIVE, SEND, FORK, JOIN, CONTENT_MODIFIED, DROP, etc. Creates a complete, searchable audit trail. Typically the largest repository in active deployments. Supports Lucene-based search by FlowFile UUID, filename, processor, time range, and transit URI.