Redis: under the hood（收藏）

Redis: under the hood

How does the Redis server work?

I was curious to learn more about Redis’s internals, so I’ve been familiarizing myself with the source, largely by reading and jumping around in Emacs. After I had peeled back enough of the onion’s layers, I realized I was trying to keep track of too many details in my head, and it wasn’t clear how it all hung together. I decided to write out in narrative form how an instance of the Redis server starts up and initializes itself, and how it handles the request/response cycle with a client, as a way of explaining it to myself, hopefully in a clear fashion. Luckily, Redis has a nice, clean code base that is easy to read and follow along. Armed with a TAGSfile, my $EDITOR, and GDB, I set out to see how it all works under the hood. (Incidentally, I was working with the Redis code base as ofcommit b4f2e41. Of course, internals such as I outline below are subject to change. However, the broad architecture of the server is unlikely to change very much, and I tried to keep that in mind as I went along.)

This article examines server startup and takes a high-level view of the request/response processing cycle. In a subsequent article, I’ll dive in to greater detail and trace a simple SET/GET command pair as they make their way through Redis.

• Redis: under the hood
  • Startup
    • Beginning global server state initialization
    • Setting up command table
    • Loading config file
    • initServer()
      • Shared objects
        • Shared integers
      • Event loop
      • Databases
      • TCP socket
      • Server cron
      • Registering connection handler with event loop
      • Opening the AOF
    • Back up to main()
      • Restoring data
      • Event loop setup
      • Entering the event loop
  • Processing a request & returning a response
    • Handling a new connection
    • Reading a command from a client
    • Executing the command and responding
  • Summary
  • Next time — tracing a SET and GET

Startup

Let’s begin with the main() function in redis.c.

Beginning global server state initialization

First, initServerConfig() is called. This partially initializes a variable server, which has the type struct redisServer, that serves as the global server state.

// redis.h:338
struct redisServer {
    pthread_t mainthread;
    int port;
    int fd;
    redisDb *db;
    // ...
};

// redis.c:69
struct redisServer server; /* server global state */

There are a huge number of members in this struct, but they generally fall into the following categories:

• general server state
• statistics
• configuration from config file
• replication
• sort parameters
• virtual memory config, state, I/O threads, & stats
• zip structure
• event loop helpers
• pub/sub

更多请点击：http://pauladamsmith.com/articles/redis-under-the-hood.html