redis/redis
Glossary
A reference of project-specific terms and acronyms used in this codebase. When a term has a dedicated page, that page is linked.
| Term | Meaning |
|---|---|
| AOF | Append-Only File. A write-ahead log of every mutating command. See Persistence. The implementation is in src/aof.c. |
| ACL | Access Control List. The user/permission model introduced in Redis 6. See ACL & security and src/acl.c. |
| ae | "asynchronous events". The internal event loop library in src/ae.c plus pluggable backends ae_epoll.c, ae_kqueue.c, ae_evport.c, ae_select.c. |
| bio | Background I/O. Three named worker threads in src/bio.c that process queues of close/fsync/lazy-free jobs without blocking the main loop. |
| C_OK / C_ERR / C_RETRY | Standard return codes used throughout src/. Defined in src/server.h. |
| client | A connected RESP peer represented by struct client in src/server.h. Clients carry a query buffer, output buffers, current command, and replication/scripting flags. |
| cluster bus | The binary protocol over tcp_port + 10000 that cluster nodes use to gossip state. See src/cluster_legacy.c. |
| cron | The periodic callback serverCron() in src/server.c that runs HZ times per second to do active expiration, eviction, stats, and child reaping. |
| DBID | The numeric index of a logical database (SELECT 0..15 by default). Each redisDb in server.db[] is a self-contained kvstore. |
| dict | The general-purpose hash table in src/dict.c. Uses incremental rehashing and supports per-bucket linked-list chaining. |
| diskless replication | Streaming the full RDB sync directly over the replica socket without writing it to disk first. See Replication. |
| ebuckets | "Expiration buckets". The bucketed time-ordered structure used to store TTLs efficiently. src/ebuckets.c. |
| estore | Expiration store, a thin wrapper around ebuckets. src/estore.c. |
| fastlock | A spinlock primitive used inside the iothreads handoff. |
| functions | Server-side stored programs. Successor to scripting (EVAL). Lua-only today; supports atomic loading via FUNCTION LOAD. src/functions.c. |
| gcra | Generic Cell Rate Algorithm. The token-bucket primitive used for client side rate limits. src/gcra.c. |
| HFE | Hash-Field Expiration. Per-field TTLs on hash entries (Redis 7.4+). See src/t_hash.c and src/keymeta.c. |
| hotkeys | Tracking of frequently accessed keys for OBJECT FREQ/sampling. src/hotkeys.c. |
| HZ | The base frequency of the cron — how many times per second serverCron fires. Adapts under load. |
| intset | Sorted integer set, the encoding for small all-integer sets. src/intset.c. |
| iothread | Optional worker thread that reads and writes client sockets in parallel. src/iothread.c. |
| kvstore | The slot-aware hash table that holds keys for a database. One dict per slot in cluster mode, one dict overall in standalone. src/kvstore.c. |
| lazyfree | Asynchronous freeing of large objects via the BIO_LAZY_FREE thread. src/lazyfree.c. |
| listpack | Compact, list-encoded byte buffer that stores small lists/sets/hashes/zsets. Successor to ziplist. src/listpack.c. |
| MOVED / ASK | Cluster redirection replies. MOVED means the slot is owned by another node; ASK is a temporary redirection during slot migration. |
| multi-part AOF | The AOF format used since Redis 7 where a base RDB plus incremental AOF files are coordinated by a manifest. |
| OOM | Out of memory. Redis maps OOM to either an eviction (maxmemory) or a command-time error. |
| PSYNC / PSYNC2 | Partial replication sync. Lets a reconnecting replica resume from an offset in the replication backlog. |
| rax | Compressed radix tree. Used for stream indexes and a few internal maps. src/rax.c. |
| rdbchannel | A second TCP connection used during replication so the RDB transfer and live command stream can flow in parallel. |
| RESP | Redis Serialization Protocol. The line-based wire format. RESP2 and RESP3 are both supported; clients negotiate via HELLO. See RESP protocol. |
| robj | "Redis object". The tagged value type wrapping an encoding + a pointer to the underlying primitive. src/object.c. |
| SDS | "Simple Dynamic String". The length-prefixed string type used everywhere. src/sds.c. |
| slot | One of 16384 hash slots in cluster mode. slot = CRC16(key) % 16384, with hash tags {...} honoured. |
| slowlog | Ring buffer of commands that exceeded the slowlog threshold. src/slowlog.c. |
| t_*.c | Type implementation files: t_string.c, t_list.c, t_set.c, t_zset.c, t_hash.c, t_stream.c. |
| tracking | Server-assisted client-side caching. src/tracking.c. |
| TTL | Time to live. Expiration metadata stored in estore. |
| vector set | A new Redis data type for vector similarity search using HNSW. Lives in modules/vector-sets/. |
| zmalloc | Redis's tracking malloc wrapper. Counts allocated bytes for INFO memory. src/zmalloc.c. |
Source-name suffix conventions
| Suffix | Meaning |
|---|---|
_legacy |
The pre-current implementation kept around for compatibility (e.g. cluster_legacy.c is the original cluster transport). |
_asm |
"Auto Slot Migration" or assembly-style cluster operations. cluster_asm.c. |
_helper |
Helper functions that don't belong in the main module (e.g. geohash_helper.c). |
Command |
A function suffix (getCommand, setCommand, …) marking the entry point invoked from the command table. |
Conventional command-flag terms
| Flag | Meaning |
|---|---|
write, readonly, denyoom, admin, pubsub, noscript, random, sort_for_script, loading, stale, skip_monitor, skip_slowlog, asking, fast, no_auth, may_replicate, sentinel |
Bits on redisCommand.flags. They drive ACL evaluation, replication, cluster routing, and slowlog inclusion. The full list is in src/server.h. |
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