Redis 如何分析慢查詢操作？
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)、傳送回覆等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儲存在記憶體裡面，讀寫速度非常快，因此你可以放心地使用它，不必擔心因為開啟slow log而損害Redis的速度。
慢查詢引數
首先來關注下慢日誌分析對應的兩個引數：
1、slowlog-log-slower-than：預設閥值，即記錄超過多少時間的記錄，預設為10000微秒，即10毫秒。
2、slowlog-max-len：記錄慢查詢的條數，預設為128條，當超過設定的條數時最早進入佇列的將被移除。線上建議增大數值，如：1000，這樣可減少佇列移除的頻率。
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對這兩個引數進行調整，或者在配置檔案中設定。
################################## 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