How Redis Starts: A Deep Dive into server.c Initialization

Assuming Redis is installed in /usr/local/, it can be started with /usr/local/bin/redis-server -c xxx.conf. The executable is built from server.c, so the startup sequence begins in the main function of that file.

The source code is available at https://github.com/hoohack/read-redis-src/blob/master/redis-4.0/src/server.c. Reading main reveals five major steps:

Initialize the redisServer structure.

Load parameters from the configuration file.

Initialize server internals.

Load persistence files to restore the database.

Start the event loop and begin listening for connections.

Initialize server structure

The initServerConfig function sets default values for many fields, such as server ID, default port (6379), LRU clock, replication settings, command table, and slow‑query parameters. It also records the executable path and command‑line arguments for later restarts:

struct redisServer server;
server.executable = getAbsolutePath(argv[0]);
server.exec_argv = zmalloc(sizeof(char*)*(argc+1));
server.exec_argv[argc] = NULL;
for (j = 0; j < argc; j++) server.exec_argv[j] = zstrdup(argv[j]);

Load parameters from configuration file

If a configuration file is specified, loadServerConfig parses it, skipping empty lines and comments, splitting each line into key/value pairs, validating them, and applying the settings to the redisServer structure.

Initialize server data structures

The initServer function creates essential runtime structures, including process ID, client and replica lists, shared objects, the event loop, TCP listening socket, database instances, cron timer, AOF handling, slow‑query log, and background I/O modules.

Load persistence files

Depending on the persistence mode, Redis either restores data from an AOF file or loads an RDB snapshot, ensuring the in‑memory database reflects the last saved state.

Start listening for events

The main function registers beforeSleep and afterSleep callbacks, then calls aeMain to start the event loop. aeMain runs an infinite loop that repeatedly invokes the callbacks and processes events with

aeProcessEvents(eventLoop, AE_ALL_EVENTS|AE_CALL_AFTER_SLEEP)

:

void aeMain(aeEventLoop *eventLoop) {
    eventLoop->stop = 0;
    while (!eventLoop->stop) {
        if (eventLoop->beforesleep != NULL)
            eventLoop->beforesleep(eventLoop);
        aeProcessEvents(eventLoop, AE_ALL_EVENTS|AE_CALL_AFTER_SLEEP);
    }
}