Redis-09.慢查询

慢查询指的是redis命令的执行时间，不包括网络传输和排队时间。

Redis配置文件redis.conf中描述慢查询相关的选项在SLOW LOG部分

################################## 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-than 10000

# 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-len 128

也可以使用config get及config set来查询和修改，config rewrite可以写入配置文件。此外，slowlog命令还可以完成一些慢查询日志相关的其它操作。

# 命令执行超过多少微秒就记录慢查询日志（1秒=1000毫秒=1000000微秒）
127.0.0.1:6379> CONFIG GET slowlog-log-slower-than
1) "slowlog-log-slower-than"
2) "10000"
# 慢查询日志保存的最大条数
127.0.0.1:6379> config get slowlog-max-len
1) "slowlog-max-len"
2) "128"
# 获取慢查询日志列表当前长度
127.0.0.1:6379> slowlog len
(integer) 0
# 获取慢查询
127.0.0.1:6379> slowlog get
# 重置慢查询
127.0.0.1:6379> slowlog reset
OK

一条慢查询日志包括4个属性：日志id、命令执行的时间戳、命令耗时、命令和参数。