來源：Java技術棧

鏈接：https://www.jianshu.com/p/27502a60fcdc

什麼是慢查詢

和mysql的慢SQL日誌分析一樣，redis也有類似的功能，來幫助定位一些慢查詢操作。

Redis slowlog是Redis用來記錄查詢執行時間的日誌系統。

查詢執行時間指的是不包括像客戶端響應(talking)、發送回覆等IO操作，而單單是執行一個查詢命令所耗費的時間。

另外，slow log保存在內存裏面，讀寫速度非常快，因此你可以放心地使用它，不必擔心因爲開啓slow log而損害Redis的速度。

慢查詢參數

首先來關注下慢日誌分析對應的兩個參數：

1、slowlog-log-slower-than：預設閥值，即記錄超過多少時間的記錄，默認爲10000微秒，即10毫秒。

2、slowlog-max-len：記錄慢查詢的條數，默認爲128條，當超過設置的條數時最早進入隊列的將被移除。線上建議增大數值，如：1000，這樣可減少隊列移除的頻率。

127.0.0.1:6379> config get slowlog-log-slower-than
1) "slowlog-log-slower-than"
2) "10000"
127.0.0.1:6379> config get slowlog-max-len
1) "slowlog-max-len"
2) "128"

可以用config set對這兩個參數進行調整，或者在配置文件中設置。

################################## 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-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

慢查詢命令

語法：slowlog subcommand [argument]

如，進行查詢慢查詢、獲取慢查詢記錄的數量、重置慢查詢日誌等操作：

192.168.10.38:9001> slowlog get
(empty list or set)
192.168.10.38:9001> slowlog get 10
(empty list or set)
192.168.10.38:9001> slowlog len 
(integer) 0
192.168.10.38:9001> slowlog reset
OK