redis-server

The main Redis daemon. Holds the dataset in memory, accepts client connections, executes commands, persists to disk, and replicates to followers.

Entry point

int main(int argc, char **argv) lives at the bottom of src/server.c (around line 7865). It does, in order:

1. Initialise libraries (zmalloc OOM handler, time zone, RNG, CRC tables, dict hash seed).
2. Detect Sentinel mode and redis-check-rdb/redis-check-aof invocation by examining argv[0].
3. Initialise the global server config (initServerConfig), the ACL subsystem (ACLInit), the modules system (moduleInitModulesSystem), the connection types (connTypeInitialize), and per-key metadata (keyMetaInit).
4. Parse the configuration file and command-line overrides into the redisServer struct.
5. Daemonise if requested (daemonize).
6. Load any modules listed in loadmodule directives.
7. Initialise the server: bind sockets, set up timers, allocate the kvstore for each DB, prime the slot map for cluster mode, restore from RDB/AOF if a file is present.
8. Enter aeMain(server.el) — the event loop runs until shutdown.

After exit, aeMain returns and the process tears down.

Modes

The same binary runs in one of three modes:

Mode	Triggered by	What changes
Standalone	Default	Single-DB or 16-DB; no cluster bus; no Sentinel commands.
Cluster	cluster-enabled yes	A single DB; cluster bus on port + 10000; gossip; slot migration; failover. See Cluster.
Sentinel	redis-sentinel, --sentinel, or argv[0] ending in redis-sentinel	Different command table; different cron; monitors a list of masters/replicas. See Sentinel.

Source layout (the redis-server slice)

The redis-server build links a long list of .o files (see REDIS_SERVER_OBJ in src/Makefile). Conceptually they group into:

Group	Files
Core orchestration	server.c, config.c, commands.c, commands.def, debug.c, monotonic.c, setcpuaffinity.c, setproctitle.c, syncio.c, syscheck.c, crash report (in debug.c)
Event loop	ae.c, ae_epoll.c, ae_kqueue.c, ae_evport.c, ae_select.c
Network	networking.c, connection.c, socket.c, unix.c, tls.c, anet.c
RESP	resp_parser.c, call_reply.c, logreqres.c
Data primitives	sds.c, dict.c, kvstore.c, quicklist.c, listpack.c, ziplist.c, zipmap.c, intset.c, rax.c, adlist.c, mstr.c, entry.c, keymeta.c, ebuckets.c, estore.c, fwtree.c, hotkeys.c, vector.c
Type implementations	t_string.c, t_list.c, t_set.c, t_zset.c, t_hash.c, t_stream.c, bitops.c, geo.c, geohash.c, geohash_helper.c, hyperloglog.c, gcra.c, stream.h, plus the vector-set sources
Persistence	rdb.c, aof.c, redis-check-rdb.c, redis-check-aof.c, chk.c, rio.c, lzf_c.c, lzf_d.c, crc16.c, crc64.c, crcspeed.c, crccombine.c, sha1.c, sha256.c, siphash.c, endianconv.c
Replication	replication.c
Cluster	cluster.c, cluster_legacy.c, cluster_asm.c, cluster_slot_stats.c
Sentinel	sentinel.c
Memory	zmalloc.c, lazyfree.c, evict.c, expire.c, defrag.c, childinfo.c, memtest.c, memory_prefetch.c
Pub/Sub & tracking	pubsub.c, notify.c, tracking.c, blocked.c, timeout.c
Scripting	eval.c, script.c, script_lua.c, function_lua.c, functions.c
Modules	module.c
ACL & auth	acl.c
Threads	bio.c, iothread.c, threads_mngr.c, eventnotifier.c
Misc	slowlog.c, latency.c, sparkline.c, lolwut.c, lolwut5.c, lolwut6.c, lolwut8.c, localtime.c, release.c, mt19937-64.c, rand.c, pqsort.c, sort.c, strl.c, util.c, multi.c, fast_float_strtod.c

Server state: the redisServer struct

A single global struct redisServer server lives in src/server.c. It is the top of the runtime tree and holds:

• The event loop (server.el).
• The array of databases (server.db[], length dbnum).
• The list of connected clients (server.clients).
• Replication state (master link, replicas list, backlog).
• Cluster state pointer (server.cluster).
• Persistence configuration and child PIDs (server.aof_state, server.rdb_child_pid, …).
• Statistics (server.stat_*).
• Per-thread mainThread queues for IO threads.

Almost every command has access to it via server.<field>. The struct definition is in src/server.h (~3,000 lines around the struct redisServer definition).

Cron and beforeSleep

The main loop's two callbacks are:

• serverCron (registered via aeCreateTimeEvent) — fires server.hz times per second (default 10, adapts under load up to 500). Does active expiration, eviction, replication housekeeping, cluster cron, AOF rewrite scheduling, and dataset housekeeping.
• beforeSleep — called every iteration before the loop blocks in epoll_wait. Drains pending writes, flushes AOF, processes blocked clients, processes lazy-free queue messages, sends cluster bus packets.

The split between cron-time and beforeSleep work is significant. Anything that has to happen before the next epoll_wait (e.g. flush a pending reply) goes in beforeSleep. Anything that runs on a fixed cadence goes in serverCron.

Shutdown

SHUTDOWN [SAVE|NOSAVE] [NOW] [FORCE] [ABORT] invokes prepareForShutdown in src/server.c. It tries to:

1. Stop accepting new clients.
2. Wait for replicas to catch up (within shutdown-timeout).
3. Save the RDB if requested.
4. Close the AOF cleanly.
5. Disconnect modules.
6. exit(0).

SHUTDOWN ABORT cancels a previously-issued SHUTDOWN if it is still pending replica acknowledgement.

Active contributors

Active contributors: antirez, Oran Agra, Pieter Noordhuis, Binbin, Yossi Gottlieb, debing.sun.

Where to start modifying

• Add a configuration option → src/config.c table + redis.conf doc.
• Add a command → see the Development workflow. New entry in src/commands/, regenerate src/commands.def, implement in the appropriate src/t_*.c.
• Change cron behaviour → serverCron in src/server.c. Be careful: any cron change has perf implications.
• Tweak shutdown → prepareForShutdown and finishShutdown in src/server.c.

Related pages

• Event loop
• Networking
• Persistence
• Replication
• Cluster
• Modules