mithril

Command handling

Every command mithril accepts is in a static table carrying its arity, flags, key positions and routing kind. Unknown commands get ERR unknown command without touching a backend.

Routed by key slot

Single-key commands (strings, hashes, lists, sets, sorted sets, streams, geo, bitmaps, HyperLogLog updates, EXPIRE family, SORT, per-key scans HSCAN/SSCAN/ZSCAN, …) hash their key and go to the owning master — or to a replica when read splitting applies and the command is read-only. Multi-key commands with single-node semantics (RENAME, SMOVE, MSETNX, BITOP, the *STORE family, RPOPLPUSH, …) route by their first key; the owning node enforces same-slot, exactly as a direct cluster connection would. EVAL routes by its first key (or any master when it has none).

Fanned out per slot

MGET, MSET, DEL, UNLINK, EXISTS, TOUCH and PFCOUNT split per slot, execute in parallel, and merge: MGET order-preserving, MSET all-OK, the rest summed. A redirected part is retried once against its new owner before merging.

Cluster-wide

SCAN iterates the whole cluster with synthetic cursors (master index packed into the cursor’s high bits), DBSIZE sums all masters, FLUSHALL broadcasts and requires every master to acknowledge.

Transactions

MULTI queues key-addressed commands locally, enforcing single-slot at queue time (CROSSSLOT otherwise); EXEC ships the whole transaction as one native MULTI/EXEC to the owning master. DISCARD is supported; WATCH is not.

Blocking and pubsub

BLPOP, BRPOP, BRPOPLPUSH, BZPOPMAX, BZPOPMIN and blocking XREAD run on dedicated backend connections and always on the slot’s master. (P)SUBSCRIBE/(P)UNSUBSCRIBE run over a per-client pubsub connection with fully ordered confirmations; PUBLISH and PUBSUB forward to a master. Under RESP3, subscribed clients may keep issuing regular commands.

Answered by the proxy

PING, ECHO, SELECT (db 0 only), TIME, AUTH, HELLO, RESET, QUIT, INFO, CONFIG (GET; SET accepts only loglevel), CLIENT (ID/SETNAME/GETNAME), COMMAND (table introspection), ACL WHOAMI, MULTI/EXEC/DISCARD, and the CLUSTER family. CLUSTER INFO/MYID/KEYSLOT/NODES/SLOTS/SHARDS describe a single virtual node owning slots 0-16383 — the emulation that lets cluster-aware clients treat the proxy as the whole cluster.

Not implemented

Requests for these return unknown-command; none of them silently misbehaves:

• scripting beyond bare EVAL: EVALSHA, SCRIPT, FUNCTION, FCALL
• shard pubsub: SSUBSCRIBE, SPUBLISH, SUNSUBSCRIBE
• newer blocking forms: BLMOVE, BLMPOP, BZMPOP
• WATCH/UNWATCH, FLUSHDB, cluster-wide KEYS
• server management: WAIT, OBJECT, DEBUG, LATENCY, MEMORY, SHUTDOWN, FAILOVER, REPLICAOF, SAVE/BGSAVE, DUMP/RESTORE, MIGRATE and similar

RANDOMKEY samples one random master’s keyspace, not the whole cluster.

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