Redis如何分析慢查询操作？

什么是慢查询

和mysql的慢SQL日志分析一样，redis也有类似的功能，来帮助定位一些慢查询操作。

Redis slowlog是Redis用来记录查询执行时间的日志系统。

查询执行时间指的是不包括像客户端响应(talking)、发送回复等IO操作，而单单是执行一个查询命令所耗费的时间。

另外，slow log保存在内存里面，读写速度非常快，因此你可以放心地使用它，不必担心因为开启slow log而损害Redis的速度。

慢查询参数

首先来关注下慢日志分析对应的两个参数：

1、slowlog-log-slower-than：预设阀值，即记录超过多少时间的记录，默认为10000微秒，即10毫秒。

2、slowlog-max-len：记录慢查询的条数，默认为128条，当超过设置的条数时最早进入队列的将被移除。线上建议增大数值，如：1000，这样可减少队列移除的频率。

127.0.0.1:6379> configgetslowlog-log-slower-than1)"slowlog-log-slower-than"2)"10000"127.0.0.1:6379> configgetslowlog-max-len1)"slowlog-max-len"2)"128"

可以用config set对这两个参数进行调整，或者在配置文件中设置。

################################## SLOW LOG ################################### # The Redis Slow Log is a system to log queries that exceeded a specified # execution time. The execution time does not include the I/O operations # like talking with the client, sending the reply and so forth, # but just the time needed to actually execute the command (this is the only # stage of command execution where the thread is blocked and can not serve # other requests in the meantime). # # You can configure the slow log with two parameters: one tells Redis # what is the execution time, in microseconds, to exceed in order for the # command to get logged, and the other parameter is the length of the # slow log. When a new command is logged the oldest one is removed from the # queue of logged commands. # The following time is expressed in microseconds, so 1000000 is equivalent # to one second. Note that a negative number disables the slow log, while # a value of zero forces the logging of every command. slowlog-log-slower-than10000# There is no limit to this length. Just be aware that it will consume memory. # You can reclaim memory used by the slow log with SLOWLOG RESET. slowlog-max-len128

慢查询命令

语法：slowlog subcommand [argument]

如，进行查询慢查询、获取慢查询记录的数量、重置慢查询日志等操作：

192.168.10.38:9001>slowlogget(emptylistorset) 192.168.10.38:9001>slowlogget10 (emptylistorset) 192.168.10.38:9001>slowloglen(integer) 0 192.168.10.38:9001>slowlogresetOK