Redis knowledge (2)

1. Redis memory storage structure

This article is based on the Redis-v2.2.4 version for analysis.

1.1 overall Redis memory storage structure

Redis supports multiple key-value databases (tables) and uses RedisDb to represent a key-value database (table ). redisServer has a redisDb * db; member variable. During RedisServer initialization, A redisDb array is created based on the number of db in the configuration file. after the client connects, SELECT a reidsDb using the SELECT command. If this parameter is not specified, the default value is redisDb. after a client selects redisDb, subsequent operations are performed on this redisDb. the memory structure of redisDb is described in detail below.

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Redis memory storage structure

RedisDb definition:

Typedef struct redisDb {dict * dict;/* The keyspace for this DB */dict * expires;/* Timeout of keys with a timeout set */dict * blocking_keys; /* Keys with clients waiting for data (BLPOP) */dict * io_keys;/* Keys with clients waiting for vm I/O */dict * watched_keys; /* WATCHED keys for MULTI/exec cas */int id;} redisDb;

In redisDb, dict members are related to the actual stored data. dict is defined as follows:

Typedef struct dictEntry {void * key; void * val; struct dictEntry * next;} dictEntry; typedef struct dictType {unsigned int (* hashFunction) (const void * key ); void * (* keyDup) (void * privdata, const void * key); void * (* valDup) (void * privdata, const void * obj); int (* keyCompare) (void * privdata, const void * key1, const void * key2); void (* keyDestructor) (void * privdata, void * key); void (* valDestructor) (void * privdata, void * obj);} dictType;/* This is our hash table structure. every dictionary has two of this as we * implement incremental rehashing, for the old to the new table. */typedef struct dictht {dictEntry ** table; unsigned long size; unsigned long sizemask; unsigned long used;} dictht; typedef struct dict {dictType * type; void * privdata; dictht ht [2]; int rehashidx;/* rehashing not in progress if rehashidx =-1 */int iterators;/* number of iterators currently running */} dict;

This article is from the "ant nest" blog, please be sure to keep this source http://feihan21.blog.51cto.com/1364153/1300007