Memcached stats 命令：掌握缓存系统运行状态的钥匙
在现代 Web 应用开发中，缓存技术扮演着至关重要的角色。它能有效减轻数据库压力、提升页面响应速度，是构建高性能系统的基础组件之一。而 Memcached 作为最经典的分布式内存缓存系统，广泛应用于各类高并发场景。但你是否曾想过：如何知道 Memcached 正在“忙”什么？缓存命中率如何？是否出现了内存不足？这些问题的答案，就藏在一条简单却强大的命令里——Memcached stats 命令。
这条命令就像缓存系统的“体检报告”，能让你清晰看到系统当前的运行状态、性能指标和资源使用情况。无论你是刚接触缓存的初学者，还是有一定经验的中级开发者，掌握它都至关重要。接下来，我们就一步步揭开它的神秘面纱。
什么是 Memcached stats 命令？
Memcached 是一个基于内存的键值存储系统，它不持久化数据，而是将数据存储在 RAM 中，从而实现极快的读写速度。但正因为数据在内存中，我们无法直接“看到”它的内部运行状态，这就需要借助命令行工具来获取信息。
Memcached stats 命令就是与 Memcached 服务通信、获取其运行时统计信息的核心命令。它通过 Telnet 或 telnet 命令连接到 Memcached 服务的默认端口（通常是 11211），发送一条 stats 指令，然后接收返回的详细数据。
这个命令本身并不修改任何数据，属于只读操作，非常适合用于监控和排查问题。
💡 类比理解：你可以把 Memcached 想象成一个智能快递柜，而
stats命令就是你打开柜门查看内部状态的“管理面板”——它告诉你有多少格子被占用了，哪些包裹在等待取件，系统是否过载等。
如何使用 Memcached stats 命令？
使用 stats 命令非常简单，只需要一个支持 Telnet 的终端工具即可。以下是完整操作流程：
telnet localhost 11211
执行后，如果连接成功，你会看到类似如下提示：
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
接着输入 stats 并回车：
stats
服务端会返回大量信息，格式如下：
STAT pid 12345
STAT uptime 3600
STAT time 1712345678
STAT version 1.6.15
STAT pointer_size 8
STAT rusage_user 0.120000
STAT rusage_system 0.080000
STAT curr_connections 10
STAT total_connections 100
STAT connection_structures 12
STAT reserved_fds 20
STAT cmd_get 5000
STAT cmd_set 2000
STAT get_hits 4500
STAT get_misses 500
STAT delete_hits 100
STAT delete_misses 20
STAT incr_hits 300
STAT incr_misses 100
STAT decr_hits 200
STAT decr_misses 50
STAT cas_hits 150
STAT cas_misses 50
STAT cas_badval 10
STAT auth_cmds 0
STAT auth_errors 0
STAT bytes_read 450000
STAT bytes_written 600000
STAT limit_maxbytes 67108864
STAT accepting_conns 1
STAT listen_disabled_num 0
STAT threads 4
STAT conn_yields 50
STAT hash_power_level 16
STAT hash_bytes 524288
STAT hash_is_expanding 0
STAT malloc_max_allowed 1073741824
STAT bytes 250000
STAT curr_items 1500
STAT total_items 2000
STAT expired_unfetched 100
STAT evicted_unfetched 50
STAT evictions 200
STAT reclaimed 150
STAT crawler_reclaimed 10
STAT lrutail_reflocked 0
STAT crawler_entries 0
STAT lru_crawler_running 0
STAT lru_maintainer_juggler 0
STAT lru_maintainer_juggler_sleep 10
STAT lru_maintainer_juggler_runs 50
STAT lru_maintainer_juggler_sleeps 50
STAT lru_maintainer_juggler_time 0.001
STAT lru_maintainer_juggler_time_total 0.050
STAT lru_maintainer_juggler_time_avg 0.001
STAT lru_maintainer_juggler_time_max 0.005
STAT lru_maintainer_juggler_time_min 0.000
STAT lru_maintainer_juggler_time_stddev 0.001
STAT lru_maintainer_juggler_time_median 0.001
STAT lru_maintainer_juggler_time_95th 0.005
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