Redis Cluster

所谓覅破解

　　Redis trunk版本，提供Cluster功能，下面我们来分析一下这个Cluster实现方式

　　


　　这里首先执行的是 processCommand
命令，代码如下


/* If this function gets called we already read a whole
* command, argments are in the client argv/argc fields.
* processCommand() execute the command or prepare the
* server for a bulk read from the client.
*/
int processCommand(redisClient *c) {
/* If cluster is enabled, redirect here */
if (server.cluster_enabled &&
!(c->cmd->getkeys_proc == NULL && c->cmd->firstkey == 0)) {
int hashslot;
if (server.cluster.state != REDIS_CLUSTER_OK) {
addReplyError(c,"The cluster is down. Check with CLUSTER INFO for more information");
return REDIS_OK;
} else {
int ask;
clusterNode *n = getNodeByQuery(c,c->cmd,c->argv,c->argc,&hashslot,&ask);
if (n == NULL) {
addReplyError(c,"Multi keys request invalid in cluster");
return REDIS_OK;
} else if (n != server.cluster.myself) {
addReplySds(c,sdscatprintf(sdsempty(),
"-%s %d %s:%d\r\n", ask ? "ASK" : "MOVED",
hashslot,n->ip,n->port));
return REDIS_OK;
}
}
}
}
　　在这里我们看到，server.cluster_enabled = True
将直接跳转到，cluster处理逻辑

　　活动cluster node 的函数是下面这句


clusterNode *n = getNodeByQuery(c,c->cmd,c->argv,c->argc,&hashslot,&ask);
　　那么redis是如何获得cluster的哪，getNoteByQuery
代码如下


/* This is the first key we see. Check what is the slot
* and node. */
firstkey = margv[keyindex[j]];
slot = keyHashSlot((char*)firstkey->ptr, sdslen(firstkey->ptr));
n = server.cluster.slots[slot];
return n
 　　  现在我们知道了是通过 keyHashSlot
获得的，那么具体实现哪？


unsigned int keyHashSlot(char *key, int keylen) {
return crc16(key,keylen) & 0x0FFF;
}
 　　 哦，原来crc16 但是请注意 &x0FFF, 其实就是 2＊＊12 ＝ 4096 ，将集群的范围控制在了4096个，这个大家要注意啦

　　  那么继续，我们获得了server 节点，接下来就要执行命令了 我们看到的是 addReplySds




} else if (n != server.cluster.myself) {
addReplySds(c,sdscatprintf(sdsempty(),
"-%s %d %s:%d\r\n", ask ? "ASK" : "MOVED",
hashslot,n->ip,n->port));
return REDIS_OK;
}
 　　下面是
addReplySds
的实现,这里大家对SDS可能有疑惑，SDSLib, A C dynamic strings library





void addReplySds(redisClient *c, sds s) {
if (_installWriteEvent(c) != REDIS_OK) {
/* The caller expects the sds to be free'd. */
sdsfree(s);
return;
}
if (_addReplyToBuffer(c,s,sdslen(s)) == REDIS_OK) {
sdsfree(s);
} else {
/* This method free's the sds when it is no longer needed. */
_addReplySdsToList(c,s);
}
}

 　　将执行的命令放到了buffer里面，也就是放到了远程服务器去执行


/* -----------------------------------------------------------------------------
* Low level functions to add more data to output buffers.
* -------------------------------------------------------------------------- */
int _addReplyToBuffer(redisClient *c, char *s, size_t len) {
size_t available = sizeof(c->buf)-c->bufpos;
if (c->flags & REDIS_CLOSE_AFTER_REPLY) return REDIS_OK;
/* If there already are entries in the reply list, we cannot
* add anything more to the static buffer. */
if (listLength(c->reply) > 0) return REDIS_ERR;
/* Check that the buffer has enough space available for this string. */
if (len > available) return REDIS_ERR;
memcpy(c->buf+c->bufpos,s,len);
c->bufpos+=len;
return REDIS_OK;
}
　　远程服务器执行命令


/* Exec the command */
if (c->flags & REDIS_MULTI &&
c->cmd->proc != execCommand && c->cmd->proc != discardCommand &&
c->cmd->proc != multiCommand && c->cmd->proc != watchCommand)
{
queueMultiCommand(c);
addReply(c,shared.queued);
} else {
call(c);
}
return REDIS_OK;
　　 当然具体执行命令的是call
方法，如下


/* Call() is the core of Redis execution of a command */
void call(redisClient *c) {
long long dirty, start = ustime(), duration;
dirty = server.dirty;
c->cmd->proc(c);
dirty = server.dirty-dirty;
duration = ustime()-start;
c->cmd->microseconds += duration;
slowlogPushEntryIfNeeded(c->argv,c->argc,duration);
c->cmd->calls++;
if (server.appendonly && dirty)
feedAppendOnlyFile(c->cmd,c->db->id,c->argv,c->argc);
if ((dirty || c->cmd->flags & REDIS_CMD_FORCE_REPLICATION) &&
listLength(server.slaves))
replicationFeedSlaves(server.slaves,c->db->id,c->argv,c->argc);
if (listLength(server.monitors))
replicationFeedMonitors(server.monitors,c->db->id,c->argv,c->argc);
server.stat_numcommands++;
}
　　


　　那么到这里就查不多了，还有就是如何添加节点，和添加节点后的变化，大家请看

　　


　　http://redis.io/presentation/Redis_Cluster.pdf