nats-io/nats-server · error

Stream state detected prior state, could not locate msg bloc

Error message

Stream state detected prior state, could not locate msg block %d

What it means

During stream recovery, a message block marked closed (its file was missing on disk even though the block index expected it, e.g. after a crash or manual deletion) could not be located. The store rebuilds state from remaining blocks, records any lost data, and returns errPriorState so callers know prior state was superseded.

Source

Thrown at server/filestore.go:2222

		}
		if n, err := fmt.Sscanf(fi.Name(), blkScan, &index); err == nil && n == 1 {
			if index > blkIndex {
				fs.warn("Stream state outdated, found extra blocks, will rebuild")
				return errPriorState
			} else if mb, ok := fs.bim[index]; ok {
				mb.closed = false
			}
		}
	}

	var rebuild bool
	for _, mb := range fs.blks {
		if mb.closed {
			rebuild = true
			if ld, _, _ := mb.rebuildState(); ld != nil {
				fs.addLostData(ld)
			}
			fs.warn("Stream state detected prior state, could not locate msg block %d", mb.index)
		}
	}
	if rebuild {
		return errPriorState
	}

	// We check first and last seq and number of msgs and bytes. If there is a difference,
	// return and error so we rebuild from the message block state on disk.
	if !trackingStatesEqual(&fs.state, &mstate) {
		_ = os.Remove(fn)
		fs.warn("Stream state encountered internal inconsistency on recover")
		return errCorruptState
	}

	return nil
}

// Recover per-message state like TTLs and schedules. Doing a linear scan through the stream

View on GitHub (pinned to 3a66a489d2)

Solutions

1. Check for manually deleted or moved message block files under the msg dir
2. Let the rebuild complete; lost data is tracked via addLostData
3. Restore block files from backup if data loss is unacceptable

When it happens

Trigger: Thrown at server/filestore.go:2222 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of nats-io/nats-server@3a66a489d2 (2026-09-02). Data as JSON: /api/errors/984b79c12ce44559. Report an issue: GitHub.