Redis: under the hood（收藏）

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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