redis analyst (7)- redis server/client source code analyst

redis/jedis虽然代码比较少，但是很难一篇文章概况所有设计及实现细节，所以还是抓取日常工作中可能的疑问，带着问题去翻代码：

1 假设当前内存占用是10G，那么落到磁盘rdb时，是否一定也是10G？

不一定，因为一方面可以设置压缩(默认开启：rdbcompression yes)，另外一方面，假设内存中存在大量已过期数据，则也过滤掉这部分数据, dump的实现上，会遍历所有数据库（0-默认16），遍历所有数据然后保存：

int rdbSaveKeyValuePair(rio *rdb, robj *key, robj *val,
                        long long expiretime, long long now)
{
    /* Save the expire time */
    if (expiretime != -1) {
        /* If this key is already expired skip it */
        if (expiretime < now) return 0;
        if (rdbSaveType(rdb,RDB_OPCODE_EXPIRETIME_MS) == -1) return -1;
        if (rdbSaveMillisecondTime(rdb,expiretime) == -1) return -1;
    }

    /* Save type, key, value */
    if (rdbSaveObjectType(rdb,val) == -1) return -1;
    if (rdbSaveStringObject(rdb,key) == -1) return -1;
    if (rdbSaveObject(rdb,val) == -1) return -1;
    return 1;
}

2 monitor实现

void monitorCommand(client *c) {
    /* ignore MONITOR if already slave or in monitor mode */
    if (c->flags & CLIENT_SLAVE) return;

    c->flags |= (CLIENT_SLAVE|CLIENT_MONITOR);
    listAddNodeTail(server.monitors,c); //把整个客户端增加到server.monitors里面去
    addReply(c,shared.ok);
}

执行命令时：

void call(client *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 & (CMD_SKIP_MONITOR|CMD_ADMIN)))
    {
        replicationFeedMonitors(c,server.monitors,c->db->id,c->argv,c->argc); //把命令发到client去
    }

可以根据info来查询输出list的最大值。或者根据client list也可以排查问题

client_longes_output_list信息获取的方法，遍历所有client，获许对应的值，取最大值。

void getClientsMaxBuffers(unsigned long *longest_output_list,
                          unsigned long *biggest_input_buffer) {
    client *c;
    listNode *ln;
    listIter li;
    unsigned long lol = 0, bib = 0;

    listRewind(server.clients,&li);
    while ((ln = listNext(&li)) != NULL) {
        c = listNodeValue(ln);

        if (listLength(c->reply) > lol) lol = listLength(c->reply);
        if (sdslen(c->querybuf) > bib) bib = sdslen(c->querybuf);
    }
    *longest_output_list = lol;
    *biggest_input_buffer = bib;
}