知识点
- Redis的所有数据库都保存在redisServer.db数组中，而数据库的数量则由redisServer.dbnum属性保存
- 客户端通过修改目标数据库指针，让它指向redisServer.db数组中的不同元素来切换不同的数据
- 数据库主要由字典构成，所以对数据库对操作都是建立在字典操作之上对。
- 数据库的键总是一个字符串对象，而值则可以是任意一种Redis对象类型
- expires字典的键指向数据库中的某个键，而值则记录了过期时间
- Redis使用惰性删除和定期删除两种策略来删除过期的键
- RDB文件不会包含已经过期的键
- 当一个过期的键被删除后，Redis会追加一条DEL命令到现有AOF文件
- 当主Redis删除一个过期键后，它会向所有从Redis发送一条DEL命令
- 从Redis不会主动删除过期键
结构体
struct redisServer {
/* General */
// 数据库数组
redisDb *db;
// 命令表
dict *commands;
....
}
/*
* 数据库结构
*/
typedef struct redisDb {
// 键空间，包括键值对象
dict *dict; /* The keyspace for this DB */
// 保存 key 的过期时间
dict *expires; /* Timeout of keys with a timeout set */
// 正因为某个/某些 key 而被阻塞的客户端
dict *blocking_keys; /* Keys with clients waiting for data (BLPOP) */
// 某个/某些接收到 PUSH 命令的阻塞 key
dict *ready_keys; /* Blocked keys that received a PUSH */
// 正在监视某个/某些 key 的所有客户端
dict *watched_keys; /* WATCHED keys for MULTI/EXEC CAS */
// 数据库的号码
int id;
} redisDb;
键空间
redisDb结构的dict字典保存了数据库中的所有键值对，这个字典称为键空间
- 键空间的键也就是数据库的键，每个键都是一个字符串对象
- 键空间的值也就是数据库的值，每个值可以是字符串对象、列表对象、哈希表对象等等Redis对象。
查找键值对
在数据库中查找键值对，最终都是通过函数lookupKey实现的，它的代码如下：
robj *lookupKey(redisDb *db, robj *key) {
// 查找 key 对象
dictEntry *de = dictFind(db->dict,key->ptr);
// 存在？
if (de) {
// 取出 key 对应的值对象
robj *val = dictGetVal(de);
/* Update the access time for the aging algorithm.
* Don't do it if we have a saving child, as this will trigger
* a copy on write madness. */
// 如果条件允许，那么更新 lru 时间
if (server.rdb_child_pid == -1 && server.aof_child_pid == -1)
val->lru = server.lruclock;
return val;
} else {
// 不存在
return NULL;
}
}
该函数在数据库db中寻找键key对应的值对象。找到则返回值的robj结构，否则返回NULL。
根据dictFind(db->dict,key->ptr)，说明在数据库db的dict中，键是以原始字符串的形式存储的；
找到值对象val后，如果当前没有进行RDB或者AOF过程，则更新该值对象的lru属性，也就是更新该键值对的访问时间。
添加键值对
向数据库中添加键值对，是通过函数dbAdd实现的，它的代码如下：
/* Add the key to the DB. It's up to the caller to increment the reference
* counte of the value if needed.
*
* 添加给定 key - value 对到数据库
* 对 value 的引用计数处理由调用者决定
*
* The program is aborted if the key already exists.
*
* 添加只在 key 不存在的情况下进行
*/
void dbAdd(redisDb *db, robj *key, robj *val) {
// 键（字符串）
sds copy = sdsdup(key->ptr);
// 保存 键-值 对
int retval = dictAdd(db->dict, copy, val);
redisAssertWithInfo(NULL,key,retval == REDIS_OK);
if (server.cluster_enabled) SlotToKeyAdd(key);
}
首先复制键对象key中的原始字符串为copy，然后利用dictAdd，将原始字符串copy，值对象val添加到db->dict中。
如果值对象是一个列表对象，则还调用signalListAsReady，使得在该列表键上调用brpop或blpop的客户端能停止阻塞，得到相应的值；如果Redis还开启了集群功能，则调用slotToKeyAdd保存该key在cluster中的槽位号。
更新键值对
更新数据库中的某个键的值，是由函数dbOverwrite实现的，它的代码如下：
/* Overwrite an existing key with a new value. Incrementing the reference
* count of the new value is up to the caller.
* This function does not modify the expire time of the existing key.
*
* 使用新值 value 覆盖原本 key 的旧值
* 对 value 的引用计数处理由调用者决定
*
* The program is aborted if the key was not already present.
*
* 添加只在 key 存在的情况下进行
*/
void dbOverwrite(redisDb *db, robj *key, robj *val) {
// 取出节点
struct dictEntry *de = dictFind(db->dict,key->ptr);
redisAssertWithInfo(NULL,key,de != NULL);
// 用新值覆盖旧值
dictReplace(db->dict, key->ptr, val);
}
该函数主要是通过调用dictReplace实现的。
如果数据库字典db->dict中找不到key，则程序直接报错退出，保证字典中key确实存在的工作，是由调用者负责的；而且本函数也不增加键值对的引用计数，这也是由调用者完成的。
删除键
从数据库中删除键值对的操作，是由函数dbDelete实现的，它的代码如下：
/* Delete a key, value, and associated expiration entry if any, from the DB */
/*
* 从数据库中删除 key ，key 对应的值，以及对应的过期时间（如果有的话）
*/
int dbDelete(redisDb *db, robj *key) {
/* Deleting an entry from the expires dict will not free the sds of
* the key, because it is shared with the main dictionary. */
// 先删除过期时间
if (dictSize(db->expires) > 0) dictDelete(db->expires,key->ptr);
// 删除 key 和 value
if (dictDelete(db->dict,key->ptr) == DICT_OK) {
if (server.cluster_enabled) SlotToKeyDel(key);
return 1;
} else {
return 0;
}
}
首先，如果db->expires非空的话，尝试从db->expires中删除该key；然后，尝试从db->dict中删除该key，删除成功并且服务器开启了集群功能，则调用slotToKeyDel，从跳跃表server.cluster->slots_to_keys中删除该key的记录。
过期策略
1.定期删除
- 每隔一段时间，程序就对数据库进行检查，删除里面对过期键。由算法决定删除多少过期键以及检查多少隔数据库
- 缺点是执行过多会浪费CPU而执行过少者浪费内存空间
- 定期删除由activeExpireCycle实现
/*
* 主动清除过期 key
*/
void activeExpireCycle(void) {
int j, iteration = 0;
long long start = ustime(), timelimit;
/* We can use at max REDIS_EXPIRELOOKUPS_TIME_PERC percentage of CPU time
* per iteration. Since this function gets called with a frequency of
* REDIS_HZ times per second, the following is the max amount of
* microseconds we can spend in this function. */
// 这个函数可以使用的时长（毫秒）
timelimit = 1000000*REDIS_EXPIRELOOKUPS_TIME_PERC/REDIS_HZ/100;
if (timelimit <= 0) timelimit = 1;
for (j = 0; j < server.dbnum; j++) {
int expired;
redisDb *db = server.db+j;
/* Continue to expire if at the end of the cycle more than 25%
* of the keys were expired. */
do {
unsigned long num = dictSize(db->expires);
unsigned long slots = dictSlots(db->expires);
long long now = mstime();
/* When there are less than 1% filled slots getting random
* keys is expensive, so stop here waiting for better times...
* The dictionary will be resized asap. */
// 过期字典里只有 %1 位置被占用，调用随机 key 的消耗比较高
// 等 key 多一点再来
if (num && slots > DICT_HT_INITIAL_SIZE &&
(num*100/slots < 1)) break;
/* The main collection cycle. Sample random keys among keys
* with an expire set, checking for expired ones. */
// 从过期字典中随机取出 key ，检查它是否过期
expired = 0; // 被删除 key 计数
if (num > REDIS_EXPIRELOOKUPS_PER_CRON) // 最多每次可查找的次数
num = REDIS_EXPIRELOOKUPS_PER_CRON;
while (num--) {
dictEntry *de;
long long t;
// 随机查找带有 TTL 的 key ，看它是否过期
// 如果数据库为空，跳出
if ((de = dictGetRandomKey(db->expires)) == NULL) break;
t = dictGetSignedIntegerVal(de);
if (now > t) {
// 已过期
sds key = dictGetKey(de);
robj *keyobj = createStringObject(key,sdslen(key));
propagateExpire(db,keyobj);
dbDelete(db,keyobj);
decrRefCount(keyobj);
expired++;
server.stat_expiredkeys++;
}
}
/* We can't block forever here even if there are many keys to
* expire. So after a given amount of milliseconds return to the
* caller waiting for the other active expire cycle. */
// 每次进行 16 次循环之后，检查时间是否超过，如果超过，则退出
iteration++;
if ((iteration & 0xf) == 0 && /* check once every 16 cycles. */
(ustime()-start) > timelimit) return;
} while (expired > REDIS_EXPIRELOOKUPS_PER_CRON/4);
}
}
2.惰性删除
- 放任键过期不管，但是每次从键空间中获取键时，都检查取得的键是否过期，如果过期的话，就删除该键；如果没有过期，就返回该键
- 缺点是对内存不友好，过期不删除不会释放内存空间
- 惰性删除由expireIfNeeded函数实现
/*
* 如果 key 已经过期，那么将它删除，否则，不做动作。
*
* key 没有过期时间、服务器正在载入或 key 未过期时，返回 0
* key 已过期，那么返回正数值
*/
int expireIfNeeded(redisDb *db, robj *key) {
// 取出 key 的过期时间
long long when = getExpire(db,key);
// key 没有过期时间，直接返回
if (when < 0) return 0; /* No expire for this key */
/* Don't expire anything while loading. It will be done later. */
// 不要在服务器载入数据时执行过期
if (server.loading) return 0;
/* If we are running in the context of a slave, return ASAP:
* the slave key expiration is controlled by the master that will
* send us synthesized DEL operations for expired keys.
*
* Still we try to return the right information to the caller,
* that is, 0 if we think the key should be still valid, 1 if
* we think the key is expired at this time. */
// 如果服务器作为附属节点运行，那么直接返回
// 因为附属节点的过期是由主节点通过发送 DEL 命令来删除的
// 不必自主删除
if (server.masterhost != NULL) {
// 返回一个理论上正确的值，但不执行实际的删除操作
return mstime() > when;
}
/* Return when this key has not expired */
// 未过期
if (mstime() <= when) return 0;
/* Delete the key */
server.stat_expiredkeys++;
// 传播过期命令
propagateExpire(db,key);
// 从数据库中删除 key
return dbDelete(db,key);
}
为什么不使用定时删除
- 在过期键较多的情况下会占用CPU时间过多影响redis响应时间和吞吐量
- 创建一个定时器需要用到redis的时间事件，时间事件的底层实现是一个无序链表，查找一个事件时间的复杂度是O(N)，并不能高效的处理大量时间事件。
所有命令具体实现代码
/*
* Copyright (c) 2009-2012, Salvatore Sanfilippo <antirez at gmail dot com>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* * Neither the name of Redis nor the names of its contributors may be used
* to endorse or promote products derived from this software without
* specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
#include "redis.h"
#include <signal.h>
#include <ctype.h>
void SlotToKeyAdd(robj *key);
void SlotToKeyDel(robj *key);
/*-----------------------------------------------------------------------------
* C-level DB API
*----------------------------------------------------------------------------*/
/*
* 在数据库 db 中查找给定 key
*
* T = O(1)
*/
robj *lookupKey(redisDb *db, robj *key) {
// 查找 key 对象
dictEntry *de = dictFind(db->dict,key->ptr);
// 存在？
if (de) {
// 取出 key 对应的值对象
robj *val = dictGetVal(de);
/* Update the access time for the aging algorithm.
* Don't do it if we have a saving child, as this will trigger
* a copy on write madness. */
// 如果条件允许，那么更新 lru 时间
if (server.rdb_child_pid == -1 && server.aof_child_pid == -1)
val->lru = server.lruclock;
return val;
} else {
// 不存在
return NULL;
}
}
/*
* 为进行读操作而读取数据库
*/
robj *lookupKeyRead(redisDb *db, robj *key) {
robj *val;
// 检查 key 是否过期，如果是的话，将它删除
expireIfNeeded(db,key);
// 查找 key ，并根据查找结果更新命中/不命中数
val = lookupKey(db,key);
if (val == NULL)
server.stat_keyspace_misses++;
else
server.stat_keyspace_hits++;
// 返回 key 的值
return val;
}
/*
* 为进行写操作而读取数据库
*
* 这个函数和 lookupKeyRead 的区别是
* 这个函数不更新命中/不命中计数
*/
robj *lookupKeyWrite(redisDb *db, robj *key) {
expireIfNeeded(db,key);
return lookupKey(db,key);
}
/*
* 为执行读取操作而从数据库中取出给定 key 的值。
* 如果 key 不存在，向客户端发送信息 reply 。
*/
robj *lookupKeyReadOrReply(redisClient *c, robj *key, robj *reply) {
robj *o = lookupKeyRead(c->db, key);
if (!o) addReply(c,reply);
return o;
}
/*
* 为执行写入操作而从数据库中取出给定 key 的值。
* 如果 key 不存在，向客户端发送信息 reply 。
*/
robj *lookupKeyWriteOrReply(redisClient *c, robj *key, robj *reply) {
robj *o = lookupKeyWrite(c->db, key);
if (!o) addReply(c,reply);
return o;
}
/* Add the key to the DB. It's up to the caller to increment the reference
* counte of the value if needed.
*
* 添加给定 key - value 对到数据库
* 对 value 的引用计数处理由调用者决定
*
* The program is aborted if the key already exists.
*
* 添加只在 key 不存在的情况下进行
*/
void dbAdd(redisDb *db, robj *key, robj *val) {
// 键（字符串）
sds copy = sdsdup(key->ptr);
// 保存 键-值 对
int retval = dictAdd(db->dict, copy, val);
redisAssertWithInfo(NULL,key,retval == REDIS_OK);
if (server.cluster_enabled) SlotToKeyAdd(key);
}
/* Overwrite an existing key with a new value. Incrementing the reference
* count of the new value is up to the caller.
* This function does not modify the expire time of the existing key.
*
* 使用新值 value 覆盖原本 key 的旧值
* 对 value 的引用计数处理由调用者决定
*
* The program is aborted if the key was not already present.
*
* 添加只在 key 存在的情况下进行
*/
void dbOverwrite(redisDb *db, robj *key, robj *val) {
// 取出节点
struct dictEntry *de = dictFind(db->dict,key->ptr);
redisAssertWithInfo(NULL,key,de != NULL);
// 用新值覆盖旧值
dictReplace(db->dict, key->ptr, val);
}
/* High level Set operation. This function can be used in order to set
* a key, whatever it was existing or not, to a new object.
*
* 高阶 set 操作。
* 可以给一个 key 设置 value ，不管 key 是否存在。
*
* 1) The ref count of the value object is incremented.
* value 对象的引用计数已增加
* 2) clients WATCHing for the destination key notified.
* 如果有 key 正在被 WATCH ，那么告知客户端这个 key 已被修改
* 3) The expire time of the key is reset (the key is made persistent).
* key 的过期时间（如果有的话）会被重置，将 key 变为持久化的
*/
void setKey(redisDb *db, robj *key, robj *val) {
// 根据 key 的存在情况，进行 key 的写入或覆盖操作
if (lookupKeyWrite(db,key) == NULL) {
dbAdd(db,key,val);
} else {
dbOverwrite(db,key,val);
}
// 增加值的引用计数
incrRefCount(val);
// 移除旧 key 原有的过期时间（如果有的话）
removeExpire(db,key);
// 告知所有正在 WATCH 这个键的客户端，键已经被修改
signalModifiedKey(db,key);
}
/*
* 检查 key 是否存在于 DB
*
* 是的话返回 1 ，否则返回 0
*/
int dbExists(redisDb *db, robj *key) {
return dictFind(db->dict,key->ptr) != NULL;
}
/* Return a random key, in form of a Redis object.
* If there are no keys, NULL is returned.
*
* 以 Redis Object 的形式随机返回数据库中的一个 key
* 如果数据库为空，那么返回 NULL
*
* The function makes sure to return keys not already expired.
*
* 函数只返回未过期的 key
*/
robj *dbRandomKey(redisDb *db) {
struct dictEntry *de;
while(1) {
sds key;
robj *keyobj;
// 从字典中返回随机值， O(N)
de = dictGetRandomKey(db->dict);
// 数据库为空
if (de == NULL) return NULL;
// 取出值对象
key = dictGetKey(de);
keyobj = createStringObject(key,sdslen(key));
// 检查 key 是否已过期
if (dictFind(db->expires,key)) {
if (expireIfNeeded(db,keyobj)) {
decrRefCount(keyobj);
// 这个 key 已过期，继续寻找下个 key
continue; /* search for another key. This expired. */
}
}
return keyobj;
}
}
/* Delete a key, value, and associated expiration entry if any, from the DB */
/*
* 从数据库中删除 key ，key 对应的值，以及对应的过期时间（如果有的话）
*/
int dbDelete(redisDb *db, robj *key) {
/* Deleting an entry from the expires dict will not free the sds of
* the key, because it is shared with the main dictionary. */
// 先删除过期时间
if (dictSize(db->expires) > 0) dictDelete(db->expires,key->ptr);
// 删除 key 和 value
if (dictDelete(db->dict,key->ptr) == DICT_OK) {
if (server.cluster_enabled) SlotToKeyDel(key);
return 1;
} else {
return 0;
}
}
/*
* 清空所有数据库
*
* T = O(N^2)
*/
long long emptyDb() {
int j;
long long removed = 0;
// 清空所有数据库, O(N^2)
for (j = 0; j < server.dbnum; j++) {
removed += dictSize(server.db[j].dict);
// O(N)
dictEmpty(server.db[j].dict);
// O(N)
dictEmpty(server.db[j].expires);
}
// 返回清除的 key 数量
return removed;
}
/*
* 选择数据库
*
* T = O(1)
*/
int selectDb(redisClient *c, int id) {
if (id < 0 || id >= server.dbnum)
return REDIS_ERR;
c->db = &server.db[id];
return REDIS_OK;
}
/*-----------------------------------------------------------------------------
* Hooks for key space changes.
*
* Every time a key in the database is modified the function
* signalModifiedKey() is called.
*
* Every time a DB is flushed the function signalFlushDb() is called.
*----------------------------------------------------------------------------*/
/*
* 通知所有监视 key 的客户端，key 已被修改。
*
* touchWatchedKey 定义在 multi.c
*/
void signalModifiedKey(redisDb *db, robj *key) {
touchWatchedKey(db,key);
}
/*
* FLUSHDB/FLUSHALL 命令调用之后的通知函数
*
* touchWatchedKeysOnFlush 定义在 multi.c
*/
void signalFlushedDb(int dbid) {
touchWatchedKeysOnFlush(dbid);
}
/*-----------------------------------------------------------------------------
* Type agnostic commands operating on the key space
*----------------------------------------------------------------------------*/
/*
* 清空客户端当前所使用的数据库
*/
void flushdbCommand(redisClient *c) {
server.dirty += dictSize(c->db->dict);
signalFlushedDb(c->db->id);
dictEmpty(c->db->dict);
dictEmpty(c->db->expires);
addReply(c,shared.ok);
}
/*
* 清空所有数据库
*/
void flushallCommand(redisClient *c) {
signalFlushedDb(-1);
// 清空所有数据库
server.dirty += emptyDb();
addReply(c,shared.ok);
// 如果正在执行数据库的保存工作，那么强制中断它
if (server.rdb_child_pid != -1) {
kill(server.rdb_child_pid,SIGKILL);
rdbRemoveTempFile(server.rdb_child_pid);
}
if (server.saveparamslen > 0) {
/* Normally rdbSave() will reset dirty, but we don't want this here
* as otherwise FLUSHALL will not be replicated nor put into the AOF. */
int saved_dirty = server.dirty;
rdbSave(server.rdb_filename);
server.dirty = saved_dirty;
}
server.dirty++;
}
/*
* 从数据库中删除所有给定 key
*/
void delCommand(redisClient *c) {
int deleted = 0, j;
for (j = 1; j < c->argc; j++) {
if (dbDelete(c->db,c->argv[j])) {
signalModifiedKey(c->db,c->argv[j]);
server.dirty++;
deleted++;
}
}
addReplyLongLong(c,deleted);
}
/*
* 检查给定 key 是否存在
*/
void existsCommand(redisClient *c) {
expireIfNeeded(c->db,c->argv[1]);
if (dbExists(c->db,c->argv[1])) {
addReply(c, shared.cone);
} else {
addReply(c, shared.czero);
}
}
/*
* 切换数据库
*/
void selectCommand(redisClient *c) {
long id;
// id 号必须是整数
if (getLongFromObjectOrReply(c, c->argv[1], &id,
"invalid DB index") != REDIS_OK)
return;
// 不允许在集群模式下似乎用 SELECT
if (server.cluster_enabled && id != 0) {
addReplyError(c,"SELECT is not allowed in cluster mode");
return;
}
// 切换数据库
if (selectDb(c,id) == REDIS_ERR) {
addReplyError(c,"invalid DB index");
} else {
addReply(c,shared.ok);
}
}
/*
* RANDOMKEY 命令的实现
*
* 随机从数据库中返回一个键
*/
void randomkeyCommand(redisClient *c) {
robj *key;
if ((key = dbRandomKey(c->db)) == NULL) {
addReply(c,shared.nullbulk);
return;
}
addReplyBulk(c,key);
decrRefCount(key);
}
/*
* KEYS 命令的实现
*
* 查找和给定模式匹配的 key
*/
void keysCommand(redisClient *c) {
dictIterator *di;
dictEntry *de;
sds pattern = c->argv[1]->ptr;
int plen = sdslen(pattern),
allkeys;
unsigned long numkeys = 0;
void *replylen = addDeferredMultiBulkLength(c);
// 指向当前数据库的 key space
di = dictGetSafeIterator(c->db->dict);
// key 的匹配模式
allkeys = (pattern[0] == '*' && pattern[1] == '\0');
while((de = dictNext(di)) != NULL) {
sds key = dictGetKey(de);
robj *keyobj;
// 检查当前迭代到的 key 是否匹配，如果是的话，将它返回
if (allkeys || stringmatchlen(pattern,plen,key,sdslen(key),0)) {
keyobj = createStringObject(key,sdslen(key));
// 只返回不过期的 key
if (expireIfNeeded(c->db,keyobj) == 0) {
addReplyBulk(c,keyobj);
numkeys++;
}
decrRefCount(keyobj);
}
}
dictReleaseIterator(di);
setDeferredMultiBulkLength(c,replylen,numkeys);
}
/*
* DBSIZE 命令的实现
*
* 返回数据库键值对数量
*/
void dbsizeCommand(redisClient *c) {
addReplyLongLong(c,dictSize(c->db->dict));
}
/*
* LASTSAVE 命令的实现
*
* 返回数据库的最后保存时间
*/
void lastsaveCommand(redisClient *c) {
addReplyLongLong(c,server.lastsave);
}
/*
* TYPE 命令的实现
*
* 返回 key 对象类型的字符串形式
*/
void typeCommand(redisClient *c) {
robj *o;
char *type;
o = lookupKeyRead(c->db,c->argv[1]);
if (o == NULL) {
type = "none";
} else {
switch(o->type) {
case REDIS_STRING: type = "string"; break;
case REDIS_LIST: type = "list"; break;
case REDIS_SET: type = "set"; break;
case REDIS_ZSET: type = "zset"; break;
case REDIS_HASH: type = "hash"; break;
default: type = "unknown"; break;
}
}
addReplyStatus(c,type);
}
/*
* 关闭服务器
*/
void shutdownCommand(redisClient *c) {
int flags = 0;
// 选择关闭的模式
if (c->argc > 2) {
addReply(c,shared.syntaxerr);
return;
} else if (c->argc == 2) {
if (!strcasecmp(c->argv[1]->ptr,"nosave")) {
flags |= REDIS_SHUTDOWN_NOSAVE;
} else if (!strcasecmp(c->argv[1]->ptr,"save")) {
flags |= REDIS_SHUTDOWN_SAVE;
} else {
addReply(c,shared.syntaxerr);
return;
}
}
// 关闭
if (prepareForShutdown(flags) == REDIS_OK) exit(0);
addReplyError(c,"Errors trying to SHUTDOWN. Check logs.");
}
/*
* 对 key 进行改名
*/
void renameGenericCommand(redisClient *c, int nx) {
robj *o;
long long expire;
/* To use the same key as src and dst is probably an error */
if (sdscmp(c->argv[1]->ptr,c->argv[2]->ptr) == 0) {
addReply(c,shared.sameobjecterr);
return;
}
// 取出源 key
if ((o = lookupKeyWriteOrReply(c,c->argv[1],shared.nokeyerr)) == NULL)
return;
incrRefCount(o);
expire = getExpire(c->db,c->argv[1]);
// 取出目标 key
if (lookupKeyWrite(c->db,c->argv[2]) != NULL) {
// 如果目标 key 存在，且 nx FLAG 打开，那么设置失败，直接返回
if (nx) {
decrRefCount(o);
addReply(c,shared.czero);
return;
}
/* Overwrite: delete the old key before creating the new one with the same name. */
// 否则，将目标 key 删除
dbDelete(c->db,c->argv[2]);
}
// 将源对象以目标 key 的名字添加到数据库
dbAdd(c->db,c->argv[2],o);
// 如果源 key 有超时时间，那么设置新 key 的超时时间
if (expire != -1) setExpire(c->db,c->argv[2],expire);
// 删除旧的源 key
dbDelete(c->db,c->argv[1]);
signalModifiedKey(c->db,c->argv[1]);
signalModifiedKey(c->db,c->argv[2]);
server.dirty++;
addReply(c,nx ? shared.cone : shared.ok);
}
void renameCommand(redisClient *c) {
renameGenericCommand(c,0);
}
void renamenxCommand(redisClient *c) {
renameGenericCommand(c,1);
}
/*
* 将 key 从一个数据库移动到另一个数据库
*/
void moveCommand(redisClient *c) {
robj *o;
redisDb *src, *dst;
int srcid;
// 不允许在集群情况下使用
if (server.cluster_enabled) {
addReplyError(c,"MOVE is not allowed in cluster mode");
return;
}
/* Obtain source and target DB pointers */
// 记录源数据库
src = c->db;
srcid = c->db->id;
// 通过切换数据库来测试目标数据库是否存在
if (selectDb(c,atoi(c->argv[2]->ptr)) == REDIS_ERR) {
addReply(c,shared.outofrangeerr);
return;
}
// 记录目标数据库
dst = c->db;
// 切换回源数据库
selectDb(c,srcid); /* Back to the source DB */
/* If the user is moving using as target the same
* DB as the source DB it is probably an error. */
// 源数据库和目标数据库相同，直接返回
if (src == dst) {
addReply(c,shared.sameobjecterr);
return;
}
/* Check if the element exists and get a reference */
// 检查源 key 的存在性
o = lookupKeyWrite(c->db,c->argv[1]);
if (!o) {
addReply(c,shared.czero);
return;
}
/* Return zero if the key already exists in the target DB */
// 如果 key 已经存在于目标数据库，那么返回
if (lookupKeyWrite(dst,c->argv[1]) != NULL) {
addReply(c,shared.czero);
return;
}
// 将 key 添加到目标数据库
dbAdd(dst,c->argv[1],o);
incrRefCount(o);
/* OK! key moved, free the entry in the source DB */
// 删除源数据库中的 key
dbDelete(src,c->argv[1]);
server.dirty++;
addReply(c,shared.cone);
}
/*-----------------------------------------------------------------------------
* Expires API
*----------------------------------------------------------------------------*/
/*
* 移除 key 的过期时间
*/
int removeExpire(redisDb *db, robj *key) {
/* An expire may only be removed if there is a corresponding entry in the
* main dict. Otherwise, the key will never be freed. */
redisAssertWithInfo(NULL,key,dictFind(db->dict,key->ptr) != NULL);
return dictDelete(db->expires,key->ptr) == DICT_OK;
}
/*
* 为 key 设置过期时间
*/
void setExpire(redisDb *db, robj *key, long long when) {
dictEntry *kde, *de;
/* Reuse the sds from the main dict in the expire dict */
kde = dictFind(db->dict,key->ptr);
redisAssertWithInfo(NULL,key,kde != NULL);
de = dictReplaceRaw(db->expires,dictGetKey(kde));
dictSetSignedIntegerVal(de,when);
}
/* Return the expire time of the specified key, or -1 if no expire
* is associated with this key (i.e. the key is non volatile) */
/*
* 返回给定 key 的过期时间
*
* 如果给定 key 没有和某个过期时间关联（它是一个非易失 key ）
* 那么返回 -1
*/
long long getExpire(redisDb *db, robj *key) {
dictEntry *de;
/* No expire? return ASAP */
// 数据库的过期记录中没有任何数据
// 或者，过期记录中没有和 key 关联的时间
// 那么直接返回
if (dictSize(db->expires) == 0 ||
(de = dictFind(db->expires,key->ptr)) == NULL) return -1;
/* The entry was found in the expire dict, this means it should also
* be present in the main dict (safety check). */
// 确保 key 在数据库中必定存在（安全性检查）
redisAssertWithInfo(NULL,key,dictFind(db->dict,key->ptr) != NULL);
// 取出字典值中保存的整数值
return dictGetSignedIntegerVal(de);
}
/* Propagate expires into slaves and the AOF file.
* When a key expires in the master, a DEL operation for this key is sent
* to all the slaves and the AOF file if enabled.
*
* This way the key expiry is centralized in one place, and since both
* AOF and the master->slave link guarantee operation ordering, everything
* will be consistent even if we allow write operations against expiring
* keys. */
/*
* 向附属节点和 AOF 文件传播过期命令
*
* 当一个键在主节点中过期时，传播一个 DEL 命令到所有附属节点和 AOF 文件
*
* 通过将删除过期键的工作集中在主节点中，可以维持数据库的一致性。
*/
void propagateExpire(redisDb *db, robj *key) {
robj *argv[2];
// DEL 命名
argv[0] = shared.del;
// 目标键
argv[1] = key;
incrRefCount(argv[0]);
incrRefCount(argv[1]);
if (server.aof_state != REDIS_AOF_OFF)
feedAppendOnlyFile(server.delCommand,db->id,argv,2);
if (listLength(server.slaves))
replicationFeedSlaves(server.slaves,db->id,argv,2);
decrRefCount(argv[0]);
decrRefCount(argv[1]);
}
/*
* 如果 key 已经过期，那么将它删除，否则，不做动作。
*
* key 没有过期时间、服务器正在载入或 key 未过期时，返回 0
* key 已过期，那么返回正数值
*/
int expireIfNeeded(redisDb *db, robj *key) {
// 取出 key 的过期时间
long long when = getExpire(db,key);
// key 没有过期时间，直接返回
if (when < 0) return 0; /* No expire for this key */
/* Don't expire anything while loading. It will be done later. */
// 不要在服务器载入数据时执行过期
if (server.loading) return 0;
/* If we are running in the context of a slave, return ASAP:
* the slave key expiration is controlled by the master that will
* send us synthesized DEL operations for expired keys.
*
* Still we try to return the right information to the caller,
* that is, 0 if we think the key should be still valid, 1 if
* we think the key is expired at this time. */
// 如果服务器作为附属节点运行，那么直接返回
// 因为附属节点的过期是由主节点通过发送 DEL 命令来删除的
// 不必自主删除
if (server.masterhost != NULL) {
// 返回一个理论上正确的值，但不执行实际的删除操作
return mstime() > when;
}
/* Return when this key has not expired */
// 未过期
if (mstime() <= when) return 0;
/* Delete the key */
server.stat_expiredkeys++;
// 传播过期命令
propagateExpire(db,key);
// 从数据库中删除 key
return dbDelete(db,key);
}
/*-----------------------------------------------------------------------------
* Expires Commands
*----------------------------------------------------------------------------*/
/* This is the generic command implementation for EXPIRE, PEXPIRE, EXPIREAT
* and PEXPIREAT. Because the commad second argument may be relative or absolute
* the "basetime" argument is used to signal what the base time is (either 0
* for *AT variants of the command, or the current time for relative expires).
*
* 这个命令是 EXPIRE 、 PEXPIRE 、 EXPIREAT 和 PEXPIREAT 命令的实现。
*
* 命令的第二个参数可能是绝对值，也可能是相对值。
* 当执行 *AT 命令时， basetime 为 0 ，在其他情况下，它保存的就是当前的绝对时间。
*
* unit is either UNIT_SECONDS or UNIT_MILLISECONDS, and is only used for
* the argv[2] parameter. The basetime is always specified in milliesconds.
*
* unit 用于指定第二个参数的格式，它可以是 UNIT_SECONDS 或 UNIT_MILLISECONDS ，
* basetime 参数总是毫秒格式的。
*/
void expireGenericCommand(redisClient *c, long long basetime, int unit) {
dictEntry *de;
robj *key = c->argv[1],
*param = c->argv[2];
long long when; /* unix time in milliseconds when the key will expire. */
// 取出 when 参数
if (getLongLongFromObjectOrReply(c, param, &when, NULL) != REDIS_OK)
return;
// 如果 when 参数以秒计算，那么将它转换成毫秒
if (unit == UNIT_SECONDS) when *= 1000;
// 将时间设置为绝对时间
when += basetime;
// 取出键
de = dictFind(c->db->dict,key->ptr);
if (de == NULL) {
// 键不存在，返回 0
addReply(c,shared.czero);
return;
}
/* EXPIRE with negative TTL, or EXPIREAT with a timestamp into the past
* should never be executed as a DEL when load the AOF or in the context
* of a slave instance.
*
* Instead we take the other branch of the IF statement setting an expire
* (possibly in the past) and wait for an explicit DEL from the master. */
// 如果当前节点为主节点
// 并且在附属节点或者 AOF 文件中解释到了负数 TTL ，或者已经过期的绝对时间
// 那么删除 key ，并向附属节点和 AOF 发送 DEL 命令
if (when <= mstime() && !server.loading && !server.masterhost) {
robj *aux;
redisAssertWithInfo(c,key,dbDelete(c->db,key));
server.dirty++;
/* Replicate/AOF this as an explicit DEL. */
aux = createStringObject("DEL",3);
rewriteClientCommandVector(c,2,aux,key);
decrRefCount(aux);
signalModifiedKey(c->db,key);
addReply(c, shared.cone);
return;
// 否则，设置 key 的过期时间
} else {
setExpire(c->db,key,when);
addReply(c,shared.cone);
signalModifiedKey(c->db,key);
server.dirty++;
return;
}
}
void expireCommand(redisClient *c) {
expireGenericCommand(c,mstime(),UNIT_SECONDS);
}
void expireatCommand(redisClient *c) {
expireGenericCommand(c,0,UNIT_SECONDS);
}
void pexpireCommand(redisClient *c) {
expireGenericCommand(c,mstime(),UNIT_MILLISECONDS);
}
void pexpireatCommand(redisClient *c) {
expireGenericCommand(c,0,UNIT_MILLISECONDS);
}
void ttlGenericCommand(redisClient *c, int output_ms) {
long long expire, ttl = -1;
expire = getExpire(c->db,c->argv[1]);
/* If the key does not exist at all, return -2 */
if (expire == -1 && lookupKeyRead(c->db,c->argv[1]) == NULL) {
addReplyLongLong(c,-2);
return;
}
/* The key exists. Return -1 if it has no expire, or the actual
* TTL value otherwise. */
if (expire != -1) {
ttl = expire-mstime();
if (ttl < 0) ttl = -1;
}
if (ttl == -1) {
addReplyLongLong(c,-1);
} else {
addReplyLongLong(c,output_ms ? ttl : ((ttl+500)/1000));
}
}
void ttlCommand(redisClient *c) {
ttlGenericCommand(c, 0);
}
void pttlCommand(redisClient *c) {
ttlGenericCommand(c, 1);
}
void persistCommand(redisClient *c) {
dictEntry *de;
de = dictFind(c->db->dict,c->argv[1]->ptr);
if (de == NULL) {
addReply(c,shared.czero);
} else {
if (removeExpire(c->db,c->argv[1])) {
addReply(c,shared.cone);
server.dirty++;
} else {
addReply(c,shared.czero);
}
}
}
/* -----------------------------------------------------------------------------
* API to get key arguments from commands
* ---------------------------------------------------------------------------*/
int *getKeysUsingCommandTable(struct redisCommand *cmd,robj **argv, int argc, int *numkeys) {
int j, i = 0, last, *keys;
REDIS_NOTUSED(argv);
if (cmd->firstkey == 0) {
*numkeys = 0;
return NULL;
}
last = cmd->lastkey;
if (last < 0) last = argc+last;
keys = zmalloc(sizeof(int)*((last - cmd->firstkey)+1));
for (j = cmd->firstkey; j <= last; j += cmd->keystep) {
redisAssert(j < argc);
keys[i++] = j;
}
*numkeys = i;
return keys;
}
int *getKeysFromCommand(struct redisCommand *cmd,robj **argv, int argc, int *numkeys, int flags) {
if (cmd->getkeys_proc) {
return cmd->getkeys_proc(cmd,argv,argc,numkeys,flags);
} else {
return getKeysUsingCommandTable(cmd,argv,argc,numkeys);
}
}
void getKeysFreeResult(int *result) {
zfree(result);
}
int *noPreloadGetKeys(struct redisCommand *cmd,robj **argv, int argc, int *numkeys, int flags) {
if (flags & REDIS_GETKEYS_PRELOAD) {
*numkeys = 0;
return NULL;
} else {
return getKeysUsingCommandTable(cmd,argv,argc,numkeys);
}
}
int *renameGetKeys(struct redisCommand *cmd,robj **argv, int argc, int *numkeys, int flags) {
if (flags & REDIS_GETKEYS_PRELOAD) {
int *keys = zmalloc(sizeof(int));
*numkeys = 1;
keys[0] = 1;
return keys;
} else {
return getKeysUsingCommandTable(cmd,argv,argc,numkeys);
}
}
int *zunionInterGetKeys(struct redisCommand *cmd,robj **argv, int argc, int *numkeys, int flags) {
int i, num, *keys;
REDIS_NOTUSED(cmd);
REDIS_NOTUSED(flags);
num = atoi(argv[2]->ptr);
/* Sanity check. Don't return any key if the command is going to
* reply with syntax error. */
if (num > (argc-3)) {
*numkeys = 0;
return NULL;
}
keys = zmalloc(sizeof(int)*num);
for (i = 0; i < num; i++) keys[i] = 3+i;
*numkeys = num;
return keys;
}
/* Slot to Key API. This is used by Redis Cluster in order to obtain in
* a fast way a key that belongs to a specified hash slot. This is useful
* while rehashing the cluster. */
void SlotToKeyAdd(robj *key) {
unsigned int hashslot = keyHashSlot(key->ptr,sdslen(key->ptr));
zslInsert(server.cluster.slots_to_keys,hashslot,key);
incrRefCount(key);
}
void SlotToKeyDel(robj *key) {
unsigned int hashslot = keyHashSlot(key->ptr,sdslen(key->ptr));
zslDelete(server.cluster.slots_to_keys,hashslot,key);
}
unsigned int GetKeysInSlot(unsigned int hashslot, robj **keys, unsigned int count) {
zskiplistNode *n;
zrangespec range;
int j = 0;
range.min = range.max = hashslot;
range.minex = range.maxex = 0;
n = zslFirstInRange(server.cluster.slots_to_keys, range);
while(n && n->score == hashslot && count--) {
keys[j++] = n->obj;
n = n->level[0].forward;
}
return j;
}
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