redis相關知識(二)

1 Redis 記憶體儲存結構

本文是基於 Redis-v2.2.4 版本進行分析.

1.1 Redis 記憶體儲存總體結構

Redis 是支援多key-value資料庫(表)的,並用 RedisDb 來表示一個key-value資料庫(表). redisServer 中有一個 redisDb *db; 成員變數, RedisServer 在初始化時,會根據設定檔的 db 數量來建立一個 redisDb 數組. 用戶端在串連後,通過 SELECT 指令來選擇一個 reidsDb,如果不指定,則預設是redisDb數組的第1個(即下標是 0 ) redisDb. 一個用戶端在選擇 redisDb 後,其後續操作都是在此 redisDb 上進行的. 下面會詳細介紹一下 redisDb 的記憶體結構.

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redis 的記憶體儲存結構

redisDb 的定義:

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;

redisDb 中 ,dict 成員是與實際儲存資料相關的. dict 的定義如下:

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;

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