Redis学习笔记（三）redis 的键管理

typedef redisServer {
    ....
    
    // Redis数据库
    redisDb *db;
    
    ....
}

typedef struct redisClient {

    // 套接字描述符
    int fd;

    // 当前正在使用的数据库
    redisDb *db;

    // 当前正在使用的数据库的 id （号码）
    int dictid;

    // 客户端的名字
    robj *name;             /* As set by CLIENT SETNAME */

} redisClient;

redis> SELECT 1
Ok
redis[1]> 

typedef struct redisDb {
    //数据库键空间
    dict *dict;                 /* The keyspace for this DB */
    //键的过期时间，字典的值为过期事件 UNIX 时间戳
    dict *expires;              /* Timeout of keys with a timeout set */
    //正处于阻塞状态的键
    dict *blocking_keys;        /* Keys with clients waiting for data (BLPOP)*/
    //可以解除阻塞的键
    dict *ready_keys;           /* Blocked keys that received a PUSH */
    //正在被 WATCH 命令监视的键
    dict *watched_keys;         /* WATCHED keys for MULTI/EXEC CAS */
    //数据库号端
    int id;                     /* Database ID */
    //数据库键的平均 TTL，统计信息
    long long avg_ttl;          /* Average TTL, just for stats */
    //
    unsigned long expires_cursor; /* Cursor of the active expire cycle. */
    list *defrag_later;         /* List of key names to attempt to defrag one by one, gradually. */
} redisDb;

# 插入一个字符串对象
redis> SET message "hello world"
OK
# 插入包含三个元素的列表对象
redis> RPUSH alphabet "a" "b" "c"
(integer)3
# 插入包含三个元素的哈希表对象
redis> HSET book name "Redis in Action"
(integer) 1
redis> HSET book author "Josiah L. Carlson"
(integer) 1
redis> HSET book publisher "Manning"
(integer) 1

int expireIfNeeded(redisDb *db, robj *key) {

    // 判断键是否过期

    if (!keyIsExpired(db,key)) return 0;

    if (server.masterhost != NULL) return 1;

    /* 删除过期键 */

    // 增加过期键个数

    server.stat_expiredkeys++;

    // 传播键过期的消息

    propagateExpire(db,key,server.lazyfree_lazy_expire);

    notifyKeyspaceEvent(NOTIFY_EXPIRED,

        "expired",key,db->id);

    // server.lazyfree_lazy_expire 为 1 表示异步删除，否则则为同步删除

    return server.lazyfree_lazy_expire ? dbAsyncDelete(db,key) :

                                         dbSyncDelete(db,key);

}

// 判断键是否过期

int keyIsExpired(redisDb *db, robj *key) {

    mstime_t when = getExpire(db,key);

    if (when < 0) return 0; 

    if (server.loading) return 0;

    mstime_t now = server.lua_caller ? server.lua_time_start : mstime();

    return now > when;

}

// 获取键的过期时间

long long getExpire(redisDb *db, robj *key) {

    dictEntry *de;

    if (dictSize(db->expires) == 0 ||

       (de = dictFind(db->expires,key->ptr)) == NULL) return -1;

    serverAssertWithInfo(NULL,key,dictFind(db->dict,key->ptr) != NULL);

    return dictGetSignedIntegerVal(de);

}

void activeExpireCycle(int type) {

    static unsigned int current_db = 0; /* 上次定期删除遍历到的数据库ID */

    static int timelimit_exit = 0;      

    static long long last_fast_cycle = 0; /* 上次执行定期删除的时间点 */

    int j, iteration = 0;

    int dbs_per_call = CRON_DBS_PER_CALL; // 需要遍历数据库的数量

    long long start = ustime(), timelimit, elapsed;

    if (clientsArePaused()) return;

    if (type == ACTIVE_EXPIRE_CYCLE_FAST) {

        if (!timelimit_exit) return;

        // ACTIVE_EXPIRE_CYCLE_FAST_DURATION 快速定期删除的执行时长

        if (start < last_fast_cycle + ACTIVE_EXPIRE_CYCLE_FAST_DURATION*2) return;

        last_fast_cycle = start;

    }

    if (dbs_per_call > server.dbnum || timelimit_exit)

        dbs_per_call = server.dbnum;

    // 慢速定期删除的执行时长

    timelimit = 1000000*ACTIVE_EXPIRE_CYCLE_SLOW_TIME_PERC/server.hz/100;

    timelimit_exit = 0;

    if (timelimit <= 0) timelimit = 1;

    if (type == ACTIVE_EXPIRE_CYCLE_FAST)

        timelimit = ACTIVE_EXPIRE_CYCLE_FAST_DURATION; /* 删除操作花费的时间 */

    long total_sampled = 0;

    long total_expired = 0;

    for (j = 0; j < dbs_per_call && timelimit_exit == 0; j++) {

        int expired;

        redisDb *db = server.db+(current_db % server.dbnum);

        current_db++;

        do {

            // .......

            expired = 0;

            ttl_sum = 0;

            ttl_samples = 0;

            // 每个数据库中检查的键的数量

            if (num > ACTIVE_EXPIRE_CYCLE_LOOKUPS_PER_LOOP)

                num = ACTIVE_EXPIRE_CYCLE_LOOKUPS_PER_LOOP;

            // 从数据库中随机选取 num 个键进行检查

            while (num--) {

                dictEntry *de;

                long long ttl;

                if ((de = dictGetRandomKey(db->expires)) == NULL) break;

                ttl = dictGetSignedInteger

                // 过期检查，并对过期键进行删除

                if (activeExpireCycleTryExpire(db,de,now)) expired++;

                if (ttl > 0) {

                    ttl_sum += ttl;

                    ttl_samples++;

                }

                total_sampled++;

            }

            total_expired += expired;

            if (ttl_samples) {

                long long avg_ttl = ttl_sum/ttl_samples;

                if (db->avg_ttl == 0) db->avg_ttl = avg_ttl;

                db->avg_ttl = (db->avg_ttl/50)*49 + (avg_ttl/50);

            }

            if ((iteration & 0xf) == 0) { /* check once every 16 iterations. */

                elapsed = ustime()-start;

                if (elapsed > timelimit) {

                    timelimit_exit = 1;

                    server.stat_expired_time_cap_reached_count++;

                    break;

                }

            }

            /* 判断过期键删除数量是否超过 25% */

        } while (expired > ACTIVE_EXPIRE_CYCLE_LOOKUPS_PER_LOOP/4);

    }

    // .......

}

127.0.0.1:6379> config get maxmemory-policy

1) "maxmemory-policy"

2) "noeviction"