Summary

With migrate-type redis-command, migrating a slot that contains a hash
key whose name has a {tag} aborts mid-stream:

[I][slot_migrate.cc:373] The key ij/staging/{N/<rand>/<id>} successfully migrated
[E][slot_migrate.cc:203] Failed to send snapshot of slot(s) <range>.
  Error: failed to migrate a key ij/staging/{N/<rand>/<id>}:101:
  failed to migrate complex key: failed to send commands to restore a key:
  wrong response from the destination node:
  got invalid response of length 61: -MOVED <slot> <host>:<port>

The slot number returned in the MOVED reply is different from
CLUSTER KEYSLOT <key> for the same key (we saw parent=5466 and the
reported MOVED=5465). The destination is computing the slot from an
encoded sub-key buffer that does not preserve the {tag} hashtag, so
the destination's command dispatcher believes that sub-key belongs to a
different slot it does not own → MOVED, abort.

Workaround

migrate-type raw-key-value transfers each key as a RocksDB blob and
does not decompose complex keys, so the sub-key hashing path is never
exercised. The same migration that fails with redis-command completes
in seconds with raw-key-value.

We recommend documenting raw-key-value as the preferred type for
production slot migration until the redis-command path is fixed.

Repro (vanilla setup)

1. Two-shard cluster, migrate-type redis-command (current default).
2. Insert a hash with a tag: HSET ij/staging/{T1}:101 f1 v1 f2 v2.
3. Trigger slot migration that includes the slot of {T1}.
4. Migration aborts with the MOVED error above.

Versions

• Apache Kvrocks 2.15.0