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about_redis_4

Redis那些事儿 第四章命令执行过程分析

作者:陈科

联系方式:chenke1818@gmail.com

转载请说明出处:http://www.dumpcache.com/wiki/doku.php?id=about_redis_4

上一章我们分析了Redis请求协议的解析,并且将解析完的命令存入到了client的argv数组中。

接下来就是执行命令并且返回结果给客户端的过程:

1.processCommand

我们来看processCommand函数:

/* If this function gets called we already read a whole
 * command, arguments are in the client argv/argc fields.
 * processCommand() execute the command or prepare the
 * server for a bulk read from the client.
 *
 * If 1 is returned the client is still alive and valid and
 * other operations can be performed by the caller. Otherwise
 * if 0 is returned the client was destroyed (i.e. after QUIT). */
int processCommand(redisClient *c) {
    /* The QUIT command is handled separately. Normal command procs will
     * go through checking for replication and QUIT will cause trouble
     * when FORCE_REPLICATION is enabled and would be implemented in
     * a regular command proc. */
    if (!strcasecmp(c->argv[0]->ptr,"quit")) {
        addReply(c,shared.ok);
        c->flags |= REDIS_CLOSE_AFTER_REPLY;
        return REDIS_ERR;
    }

    /* Now lookup the command and check ASAP about trivial error conditions
     * such as wrong arity, bad command name and so forth. */
    c->cmd = c->lastcmd = lookupCommand(c->argv[0]->ptr);
    if (!c->cmd) {
        flagTransaction(c);
        addReplyErrorFormat(c,"unknown command '%s'",
            (char*)c->argv[0]->ptr);
        return REDIS_OK;
    } else if ((c->cmd->arity > 0 && c->cmd->arity != c->argc) ||
               (c->argc < -c->cmd->arity)) {
        flagTransaction(c);
        addReplyErrorFormat(c,"wrong number of arguments for '%s' command",
            c->cmd->name);
        return REDIS_OK;
    }

    /* Check if the user is authenticated */
    if (server.requirepass && !c->authenticated && c->cmd->proc != authCommand)
    {
        flagTransaction(c);
        addReply(c,shared.noautherr);
        return REDIS_OK;
    }

    /* Handle the maxmemory directive.
     *
     * First we try to free some memory if possible (if there are volatile
     * keys in the dataset). If there are not the only thing we can do
     * is returning an error. */
    if (server.maxmemory) {
        int retval = freeMemoryIfNeeded();
        if ((c->cmd->flags & REDIS_CMD_DENYOOM) && retval == REDIS_ERR) {
            flagTransaction(c);
            addReply(c, shared.oomerr);
            return REDIS_OK;
        }
    }

    /* Don't accept write commands if there are problems persisting on disk
     * and if this is a master instance. */
    if (((server.stop_writes_on_bgsave_err &&
          server.saveparamslen > 0 &&
          server.lastbgsave_status == REDIS_ERR) ||
          server.aof_last_write_status == REDIS_ERR) &&
        server.masterhost == NULL &&
        (c->cmd->flags & REDIS_CMD_WRITE ||
         c->cmd->proc == pingCommand))
    {
        flagTransaction(c);
        if (server.aof_last_write_status == REDIS_OK)
            addReply(c, shared.bgsaveerr);
        else
            addReplySds(c,
                sdscatprintf(sdsempty(),
                "-MISCONF Errors writing to the AOF file: %s\r\n",
                strerror(server.aof_last_write_errno)));
        return REDIS_OK;
    }

    /* Don't accept write commands if there are not enough good slaves and
     * user configured the min-slaves-to-write option. */
    if (server.masterhost == NULL &&
        server.repl_min_slaves_to_write &&
        server.repl_min_slaves_max_lag &&
        c->cmd->flags & REDIS_CMD_WRITE &&
        server.repl_good_slaves_count < server.repl_min_slaves_to_write)
    {
        flagTransaction(c);
        addReply(c, shared.noreplicaserr);
        return REDIS_OK;
    }

    /* Don't accept write commands if this is a read only slave. But
     * accept write commands if this is our master. */
    if (server.masterhost && server.repl_slave_ro &&
        !(c->flags & REDIS_MASTER) &&
        c->cmd->flags & REDIS_CMD_WRITE)
    {
        addReply(c, shared.roslaveerr);
        return REDIS_OK;
    }

    /* Only allow SUBSCRIBE and UNSUBSCRIBE in the context of Pub/Sub */
    if (c->flags & REDIS_PUBSUB &&
        c->cmd->proc != pingCommand &&
        c->cmd->proc != subscribeCommand &&
        c->cmd->proc != unsubscribeCommand &&
        c->cmd->proc != psubscribeCommand &&
        c->cmd->proc != punsubscribeCommand) {
        addReplyError(c,"only (P)SUBSCRIBE / (P)UNSUBSCRIBE / QUIT allowed in this context");
        return REDIS_OK;
    }

    /* Only allow INFO and SLAVEOF when slave-serve-stale-data is no and
     * we are a slave with a broken link with master. */
    if (server.masterhost && server.repl_state != REDIS_REPL_CONNECTED &&
        server.repl_serve_stale_data == 0 &&
        !(c->cmd->flags & REDIS_CMD_STALE))
    {
        flagTransaction(c);
        addReply(c, shared.masterdownerr);
        return REDIS_OK;
    }

    /* Loading DB? Return an error if the command has not the
     * REDIS_CMD_LOADING flag. */
    if (server.loading && !(c->cmd->flags & REDIS_CMD_LOADING)) {
        addReply(c, shared.loadingerr);
        return REDIS_OK;
    }

    /* Lua script too slow? Only allow a limited number of commands. */
    if (server.lua_timedout &&
          c->cmd->proc != authCommand &&
          c->cmd->proc != replconfCommand &&
        !(c->cmd->proc == shutdownCommand &&
          c->argc == 2 &&
          tolower(((char*)c->argv[1]->ptr)[0]) == 'n') &&
        !(c->cmd->proc == scriptCommand &&
          c->argc == 2 &&
          tolower(((char*)c->argv[1]->ptr)[0]) == 'k'))
    {
        flagTransaction(c);
        addReply(c, shared.slowscripterr);
        return REDIS_OK;
    }

    /* 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,REDIS_CALL_FULL);
        if (listLength(server.ready_keys))
            handleClientsBlockedOnLists();
    }
    return REDIS_OK;
}

该函数一共进行了几个步骤:

1.如果命令行中包含了quit,那么后面的指令将不会被执行。

2.查找相应的命令:c→cmd = c→lastcmd = lookupCommand(c→argv[0]→ptr);

3.检测命令的参数个数

4.假如服务器配置了需要密码校验的功能(server.requirepass),那么命令必须为:authCommand

5.如果服务器有最大内存限制(server.maxmemory),那么执行freeMemoryIfNeeded函数,释放一部分内存。

6.假如服务器状态出现了问题,那么停止执行命令(write,bgsave,aof等)

7.如果服务器设置了最小的slave数量限制,当slave数量小于最小slave数量的时候,停止执行命令。

8.如果服务器为slave,则不接受write命令。

9.在pub/sub的上下文时,只接受pingCommand,subscribeCommand,unsubscribeCommand,psubscribeCommand,punsubscribeCommand这几类命令。

10.当服务器为slave并且和master的连接已经断开,并且设置了跟mater断开后不再提供服务(repl_serve_stale_data),那么停止执行命令。

11.如果服务器正在装载数据中,则不接受命令。

12.如果lua脚本执行速度太慢了,则停止执行命令。

13.执行命令。

命令的执行分成2种可能,我们来看下这个逻辑

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,REDIS_CALL_FULL);
        if (listLength(server.ready_keys))
            handleClientsBlockedOnLists();
    }

2.事务处理

假如命令行是MULTI开头的,那么将会执行事务,redis的事务实现比较简单,因为本身就是单线程的,只要把命令提交到事务队列中即可,然后在收到EXEC命令的时候一并执行。

举例:

> MULTI
OK
> INCR foo
QUEUED
> INCR bar
QUEUED
> EXEC
1) (integer) 1
2) (integer) 1

具体参考:http://redis.io/topics/transactions

我们来看下queueMultiCommand函数源码:

void queueMultiCommand(redisClient *c) {
    multiCmd *mc;
    int j;

    c->mstate.commands = zrealloc(c->mstate.commands,
            sizeof(multiCmd)*(c->mstate.count+1));
    mc = c->mstate.commands+c->mstate.count;
    mc->cmd = c->cmd;
    mc->argc = c->argc;
    mc->argv = zmalloc(sizeof(robj*)*c->argc);
    memcpy(mc->argv,c->argv,sizeof(robj*)*c->argc);
    for (j = 0; j < c->argc; j++)
        incrRefCount(mc->argv[j]);
    c->mstate.count++;
}

非常简单,将命令提交到了队列中即可。

3.正常的命令执行(call函数)

假如不是MULTI类型的,那么将会执行call函数,我们来看下源码:

void call(redisClient *c, int flags) {
    long long dirty, start, duration;
    int client_old_flags = c->flags;

    /* Sent the command to clients in MONITOR mode, only if the commands are
     * not generated from reading an AOF. */
    if (listLength(server.monitors) &&
        !server.loading &&
        !(c->cmd->flags & (REDIS_CMD_SKIP_MONITOR|REDIS_CMD_ADMIN)))
    {
        replicationFeedMonitors(c,server.monitors,c->db->id,c->argv,c->argc);
    }

    /* Call the command. */
    c->flags &= ~(REDIS_FORCE_AOF|REDIS_FORCE_REPL);
    redisOpArrayInit(&server.also_propagate);
    dirty = server.dirty;
    start = ustime();
    c->cmd->proc(c);
    duration = ustime()-start;
    dirty = server.dirty-dirty;
    if (dirty < 0) dirty = 0;

    /* When EVAL is called loading the AOF we don't want commands called
     * from Lua to go into the slowlog or to populate statistics. */
    if (server.loading && c->flags & REDIS_LUA_CLIENT)
        flags &= ~(REDIS_CALL_SLOWLOG | REDIS_CALL_STATS);

    /* If the caller is Lua, we want to force the EVAL caller to propagate
     * the script if the command flag or client flag are forcing the
     * propagation. */
    if (c->flags & REDIS_LUA_CLIENT && server.lua_caller) {
        if (c->flags & REDIS_FORCE_REPL)
            server.lua_caller->flags |= REDIS_FORCE_REPL;
        if (c->flags & REDIS_FORCE_AOF)
            server.lua_caller->flags |= REDIS_FORCE_AOF;
    }

    /* Log the command into the Slow log if needed, and populate the
     * per-command statistics that we show in INFO commandstats. */
    if (flags & REDIS_CALL_SLOWLOG && c->cmd->proc != execCommand) {
        char *latency_event = (c->cmd->flags & REDIS_CMD_FAST) ?
                              "fast-command" : "command";
        latencyAddSampleIfNeeded(latency_event,duration/1000);
        slowlogPushEntryIfNeeded(c->argv,c->argc,duration);
    }
    if (flags & REDIS_CALL_STATS) {
        c->cmd->microseconds += duration;
        c->cmd->calls++;
    }

    /* Propagate the command into the AOF and replication link */
    if (flags & REDIS_CALL_PROPAGATE) {
        int flags = REDIS_PROPAGATE_NONE;

        if (c->flags & REDIS_FORCE_REPL) flags |= REDIS_PROPAGATE_REPL;
        if (c->flags & REDIS_FORCE_AOF) flags |= REDIS_PROPAGATE_AOF;
        if (dirty)
            flags |= (REDIS_PROPAGATE_REPL | REDIS_PROPAGATE_AOF);
        if (flags != REDIS_PROPAGATE_NONE)
            propagate(c->cmd,c->db->id,c->argv,c->argc,flags);
    }

    /* Restore the old FORCE_AOF/REPL flags, since call can be executed
     * recursively. */
    c->flags &= ~(REDIS_FORCE_AOF|REDIS_FORCE_REPL);
    c->flags |= client_old_flags & (REDIS_FORCE_AOF|REDIS_FORCE_REPL);

    /* Handle the alsoPropagate() API to handle commands that want to propagate
     * multiple separated commands. */
    if (server.also_propagate.numops) {
        int j;
        redisOp *rop;

        for (j = 0; j < server.also_propagate.numops; j++) {
            rop = &server.also_propagate.ops[j];
            propagate(rop->cmd, rop->dbid, rop->argv, rop->argc, rop->target);
        }
        redisOpArrayFree(&server.also_propagate);
    }
    server.stat_numcommands++;
}

我们接着分析下call函数的主要步骤:

1.假如有监视状态的客户端,那么先将命令发送给客户端:

 /* Sent the command to clients in MONITOR mode, only if the commands are
     * not generated from reading an AOF. */
    if (listLength(server.monitors) &&
        !server.loading &&
        !(c->cmd->flags & (REDIS_CMD_SKIP_MONITOR|REDIS_CMD_ADMIN)))
    {
        replicationFeedMonitors(c,server.monitors,c->db->id,c->argv,c->argc);
    }

2.执行命令: c→cmd→proc©;

3.添加慢查询日志,并记录样本

4.将命令传播到aof文件,并且发送给slave.

关于主从复制和aof的格式等我会后面单独讲解。

全部完事之后,将会执行addReply函数,将数据发送给客户端:

4.addReply

void addReply(redisClient *c, robj *obj) {
    if (prepareClientToWrite(c) != REDIS_OK) return;

    /* This is an important place where we can avoid copy-on-write
     * when there is a saving child running, avoiding touching the
     * refcount field of the object if it's not needed.
     *
     * If the encoding is RAW and there is room in the static buffer
     * we'll be able to send the object to the client without
     * messing with its page. */
    if (obj->encoding == REDIS_ENCODING_RAW) {
        if (_addReplyToBuffer(c,obj->ptr,sdslen(obj->ptr)) != REDIS_OK)
            _addReplyObjectToList(c,obj);
    } else if (obj->encoding == REDIS_ENCODING_INT) {
        /* Optimization: if there is room in the static buffer for 32 bytes
         * (more than the max chars a 64 bit integer can take as string) we
         * avoid decoding the object and go for the lower level approach. */
        if (listLength(c->reply) == 0 && (sizeof(c->buf) - c->bufpos) >= 32) {
            char buf[32];
            int len;

            len = ll2string(buf,sizeof(buf),(long)obj->ptr);
            if (_addReplyToBuffer(c,buf,len) == REDIS_OK)
                return;
            /* else... continue with the normal code path, but should never
             * happen actually since we verified there is room. */
        }
        obj = getDecodedObject(obj);
        if (_addReplyToBuffer(c,obj->ptr,sdslen(obj->ptr)) != REDIS_OK)
            _addReplyObjectToList(c,obj);
        decrRefCount(obj);
    } else {
        redisPanic("Wrong obj->encoding in addReply()");
    }
}

我们来分析下这个过程:

1.注册写事件到epoll中:prepareClientToWrite

2.调用_addReplyToBuffer将数据写到buf中.

3.假如buf不够大则调用_addReplyObjectToList函数添加到reply链表中。

本章的分析暂且到这里,下一章开始我们将会分析每一个redis命令的实现。

about_redis_4.txt · 最后更改: 2018/10/14 15:31 (外部编辑)