Lore

A narrative timeline of Redis. Dates derive from git tags, commit timestamps, and the release notes shipped in 00-RELEASENOTES.

Origins (Mar 2009 – mid 2010)

• Mar 2009. Salvatore Sanfilippo ("antirez") commits the first version of Redis to GitHub. The initial codebase is roughly one C file plus the early dict, sds, and ae implementations. Lua scripting, persistence, and clustering do not yet exist.
• 2009. RDB snapshots land. The fork-based persistence model — a child writes the snapshot while the parent keeps serving — is established and remains the design today.
• Late 2009. AOF (Append-Only File) is added as a more durable alternative to RDB.
• 2010. Pub/Sub, MULTI/EXEC transactions, and the slow-log subsystem appear. The basic data types (strings, lists, sets, hashes, sorted sets) are settled into their t_*.c files, where they still live.

The Master/Slave era (2010 – 2014)

• Oct 2010. Replication ships in the form that is still the default: a primary keeps a replication backlog and replicates writes to attached replicas. The protocol later evolves into PSYNC.
• 2012. Cluster work begins. The early code becomes src/cluster_legacy.c. Hash slot count fixes at 16384 (CRC16(key) mod 16384).
• Oct 2013. Sentinel ships in stable form. The same binary changes its command table when invoked as redis-sentinel (or with --sentinel). Fixed since then in src/sentinel.c.
• Mar 2014. Lua scripting (EVAL/EVALSHA) goes from beta to stable. The interpreter is the bundled Lua 5.1 in deps/lua/.

The Cluster era (2015 – 2018)

• Apr 2015. Redis 3.0 ships with cluster GA. Clients see MOVED/ASK redirections; clusters use the bus protocol on port + 10000.
• Apr 2017. Redis 4.0 lands the modules API. src/module.c and src/redismodule.h define a stable C ABI so external .so's can register commands and data types. PSYNC2 and active defrag (src/defrag.c) also ship with 4.0.
• 2017. Lazy free (asynchronous deletion of large objects via the BIO thread) is introduced — the start of src/lazyfree.c.
• Oct 2018. Redis 5.0 introduces streams (src/t_stream.c), the first new top-level data type in years. Internally streams are radix-tree-indexed (src/rax.c) listpacks.

The Modernisation era (2019 – 2021)

• May 2020. Redis 6.0 ships ACLs (src/acl.c), TLS (src/tls.c), the new RESP3 protocol (src/networking.c, src/resp_parser.c), client-side tracking (src/tracking.c), and the first version of optional IO threads (src/iothread.c was rewritten in 7.4 but the design originates here).
• May 2021. Redis 6.2 expands the command set significantly (COPY, SMISMEMBER, LMPOP, …) and introduces RESP3-only clients.
• Aug 2021. Multi-part AOF design lands as preparatory work for Redis 7.

The Functions and Cluster v2 era (2022 – 2024)

• Apr 2022. Redis 7.0 ships functions (src/functions.c) — server-side stored programs that supersede EVAL for production workloads — plus sharded Pub/Sub, multi-part AOF, ACL v2, client-no-evict, and a substantial cluster bus refactor.
• Jan 2023. Redis 7.2 lands CLUSTER SLOT-STATS, CLIENT NO-TOUCH, and Lua's redis.REPL_* controls. The cluster_slot_stats.c file is born.
• Mar 2024. Redis 7.4 introduces hash-field TTLs — every hash entry can carry its own expiration. The implementation pulls in src/keymeta.c and a redesigned src/ebuckets.c for bucketed expiration.
• 2024. The licence transitions from BSD-3 to a tri-license (RSALv2 / SSPLv1 / AGPLv3) under Redis Ltd.'s stewardship. LICENSE.txt is rewritten and REDISCONTRIBUTIONS.txt documents which portions remain under BSD-3.

The current era (2025 – present)

• Q2 2025. Redis 8 rebranding: "Redis Community Edition" is renamed "Redis Open Source". Core repo accepts upstream contributions for new types like vector sets (HNSW-backed similarity search) under modules/vector-sets/, plus query/search and bloom/cuckoo/topk/t-digest/cms probabilistic types are made first-class via the modules included by BUILD_WITH_MODULES=yes.
• 2025–2026. Active subsystems on the unstable branch include:
  • Auto Slot Migration (src/cluster_asm.c) — automated rebalancing across cluster nodes.
  • Hash-field TTLs continue to evolve (src/t_hash.c, src/keymeta.c).
  • Stream improvements and XDELEX/XACKDEL/XNACK semantics.
  • Hot-key tracking (src/hotkeys.c).
  • GCRA-based rate limiting primitive (src/gcra.c).
  • IO thread rewrite as a fully thread-pool model with main-thread handoff and pending-clients lists (src/iothread.c).
  • Faster floating-point conversion via fast_float_strtod.c.

Longest-standing features

These pieces date back to the earliest commits and are still in active use:

Feature	First seen	Notes
ae.c event loop	2009	Architecture has not changed; backends are pluggable.
sds.c strings	2009	One header rewrite (sds.h) but the len-prefix design stuck.
dict.c hash table	2009	Incremental rehashing is original to Redis.
t_string.c, t_list.c, t_set.c, t_zset.c, t_hash.c	2010	Encodings have changed (ziplist → listpack), but the file split has not.
rdb.c snapshotting	2009	RDB version field is bumped each compatibility break; current RDB version is in src/rdb.h.
Fork-based BGSAVE	2009	The single most influential design choice in Redis.

Deprecated and removed features

Feature	Rise	Decline
ziplist	The default encoding for small lists/hashes/zsets from the early days.	Superseded by listpack in Redis 7.0. src/ziplist.c is kept around for RDB load compatibility but isn't created any more.
zipmap	Original small-hash encoding.	Replaced by ziplist long ago; kept in src/zipmap.c only for ancient RDB compatibility.
SLAVEOF command name	The old name for REPLICAOF.	The command remains but is deprecated; new docs use REPLICAOF.
Diskful PSYNC2 as the default	Used disk transit for the RDB during full sync.	"Diskless" replication and "rdbchannel" replication are now both available as faster alternatives. Both implementations live in src/replication.c.
The lolwut command	Easter-egg drawing demo introduced for Redis's birthday.	Still in src/lolwut.c (and lolwut5.c, lolwut6.c, lolwut8.c for each major release that added a new design); not deprecated, just decorative.

Major rewrites

• Listpack supersedes ziplist (Redis 7.0, 2022). New encoding, new src/listpack.c. Every t_*.c file gained code paths for OBJ_ENCODING_LISTPACK.
• PSYNC → PSYNC2 → rdbchannel (2017–2024). Replication grew the ability to resume after primary restart and then to stream RDB on a separate socket.
• Multi-part AOF (Redis 7.0, 2022). The single appendonly.aof was split into a base RDB plus incremental AOF files coordinated by a manifest. src/aof.c doubled in size.
• Hash-field TTL (Redis 7.4, 2024). A new key-meta layer (src/keymeta.c), the entry.c/h field types, and a rewritten src/ebuckets.c to make per-field expiration cheap.
• Cluster Auto Slot Migration (2025). A new src/cluster_asm.c adds an automated slot-rebalancing controller alongside the legacy implementation.
• IO threads rewrite (2024–2025). The original Redis 6 IO threading model was reworked in src/iothread.c as a thread-pool with main-thread coordination and pending-client queues.

Growth trajectory

• 2009 — single author, single binary.
• 2013 — Sentinel adds the second runtime mode of the same binary.
• 2015 — Cluster adds the third (and last) runtime mode.
• 2017 — Modules let third parties extend the command surface without editing core.
• 2020 — TLS, ACL, RESP3, IO threads. The codebase doubles between 6.0 and 6.2 mainly because of new commands and the modules API surface.
• 2024 onward — Vector sets, query/search modules, and probabilistic types become first-class with BUILD_WITH_MODULES=yes. The repo retains its single-binary flavour but the capability surface has grown by an order of magnitude.

The shape of the project has changed less than the line count suggests. The original single-threaded event-loop core is still the heart of src/server.c; everything else has been added around it.