redis生产问题
大约 9 分钟
redis生产问题
redis bigKey排查及处理
什么是 bigkey？
简单来说，如果一个 key 对应的 value 所占用的内存比较大，那这个 key 就可以看作是 bigkey。
具体多大才算大呢？有一个不是特别精确的参考标准：string 类型的 value 超过 10 kb，复合类型的 value 包含的元素超过 5000 个。
bigkey 有什么危害？
bigkey 是指键值占用内存空间非常大的 key。例如一个字符串 a 存储了 200M 的数据。
bigkey 的主要影响有：
网络阻塞；获取 bigkey 时，传输的数据量比较大，会增加带宽的压力。
超时阻塞；因为 bigkey 占用的空间比较大，所以操作起来效率会比较低，导致出现阻塞的可能性增加。
导致内存空间不平衡；一个 bigkey 存储数据量比较大，同一个 key 在同一个节点或服务器中存储，会造成一定影响。
怎么处理
info命令查看redis占用内存以及key数量，判断是否存在大Key。
查找大key:
--bigkeys：表示统计bigkey使用情况
-i 0.1 ：表示每扫描100次会停0.1秒，防止占用过高的CPU，影响Redis节点的正常运行。非必选
-a {password}：显式的输入密码
redis-cli -a art-redis-password -i 0.1 --bigkeys
查看指定key使用内存：
memory usage {key}
用 debug object {key} 也可以查到key占用的内存。
删除key:
unlike {key}
bigkey最好不要直接del，key较大时，直接del可能会长时间阻塞线程，甚至导致崩溃。
使用unlink删除，会可返回，不会阻塞，后台有线程异步去删除key释放内存空间。
对于list、hash这样的可以使用代码删除，结合scan命令分批次渐进的删除。
redis-cli支持的参数：
./redis-cli --help
bash: ./redis-cli: No such file or directory
root@art-redis:/data# redis-cli --help
redis-cli 6.0.8
Usage: redis-cli [OPTIONS] [cmd [arg [arg ...]]]
-h <hostname> Server hostname (default: 127.0.0.1).
-p <port> Server port (default: 6379).
-s <socket> Server socket (overrides hostname and port).
-a <password> Password to use when connecting to the server.
You can also use the REDISCLI_AUTH environment
variable to pass this password more safely
(if both are used, this argument takes predecence).
--user <username> Used to send ACL style 'AUTH username pass'. Needs -a.
--pass <password> Alias of -a for consistency with the new --user option.
--askpass Force user to input password with mask from STDIN.
If this argument is used, '-a' and REDISCLI_AUTH
environment variable will be ignored.
-u <uri> Server URI.
-r <repeat> Execute specified command N times.
-i <interval> When -r is used, waits <interval> seconds per command.
It is possible to specify sub-second times like -i 0.1.
-n <db> Database number.
-3 Start session in RESP3 protocol mode.
-x Read last argument from STDIN.
-d <delimiter> Multi-bulk delimiter in for raw formatting (default: \n).
-c Enable cluster mode (follow -ASK and -MOVED redirections).
--tls Establish a secure TLS connection.
--sni <host> Server name indication for TLS.
--cacert <file> CA Certificate file to verify with.
--cacertdir <dir> Directory where trusted CA certificates are stored.
If neither cacert nor cacertdir are specified, the default
system-wide trusted root certs configuration will apply.
--cert <file> Client certificate to authenticate with.
--key <file> Private key file to authenticate with.
--raw Use raw formatting for replies (default when STDOUT is
not a tty).
--no-raw Force formatted output even when STDOUT is not a tty.
--csv Output in CSV format.
--stat Print rolling stats about server: mem, clients, ...
--latency Enter a special mode continuously sampling latency.
If you use this mode in an interactive session it runs
forever displaying real-time stats. Otherwise if --raw or
--csv is specified, or if you redirect the output to a non
TTY, it samples the latency for 1 second (you can use
-i to change the interval), then produces a single output
and exits.
--latency-history Like --latency but tracking latency changes over time.
Default time interval is 15 sec. Change it using -i.
--latency-dist Shows latency as a spectrum, requires xterm 256 colors.
Default time interval is 1 sec. Change it using -i.
--lru-test <keys> Simulate a cache workload with an 80-20 distribution.
--replica Simulate a replica showing commands received from the master.
--rdb <filename> Transfer an RDB dump from remote server to local file.
--pipe Transfer raw Redis protocol from stdin to server.
--pipe-timeout <n> In --pipe mode, abort with error if after sending all data.
no reply is received within <n> seconds.
Default timeout: 30. Use 0 to wait forever.
--bigkeys Sample Redis keys looking for keys with many elements (complexity).
--memkeys Sample Redis keys looking for keys consuming a lot of memory.
--memkeys-samples <n> Sample Redis keys looking for keys consuming a lot of memory.
And define number of key elements to sample
--hotkeys Sample Redis keys looking for hot keys.
only works when maxmemory-policy is *lfu.
--scan List all keys using the SCAN command.
--pattern <pat> Keys pattern when using the --scan, --bigkeys or --hotkeys
options (default: *).
--intrinsic-latency <sec> Run a test to measure intrinsic system latency.
The test will run for the specified amount of seconds.
--eval <file> Send an EVAL command using the Lua script at <file>.
--ldb Used with --eval enable the Redis Lua debugger.
--ldb-sync-mode Like --ldb but uses the synchronous Lua debugger, in
this mode the server is blocked and script changes are
not rolled back from the server memory.
--cluster <command> [args...] [opts...]
Cluster Manager command and arguments (see below).
--verbose Verbose mode.
--no-auth-warning Don't show warning message when using password on command
line interface.
--help Output this help and exit.
--version Output version and exit.
Cluster Manager Commands:
Use --cluster help to list all available cluster manager commands.
Examples:
cat /etc/passwd | redis-cli -x set mypasswd
redis-cli get mypasswd
redis-cli -r 100 lpush mylist x
redis-cli -r 100 -i 1 info | grep used_memory_human:
redis-cli --eval myscript.lua key1 key2 , arg1 arg2 arg3
redis-cli --scan --pattern '*:12345*'
(Note: when using --eval the comma separates KEYS[] from ARGV[] items)
When no command is given, redis-cli starts in interactive mode.
Type "help" in interactive mode for information on available commands
and settings.