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Today, the editor will share with you the relevant knowledge points about how to use the Redis slow query log. The content is detailed and the logic is clear. I believe most people still know too much about this knowledge, so share this article for your reference. I hope you can get something after reading this article.

What is a slow log called SLOW LOG?

Slow log is a logging system used by Redis to record command requests that take longer than a given length of time to execute a query. Query execution time refers to the time it takes to execute a query command, excluding IO operations such as client response (talking) and sending replies. In addition, slow log is stored in memory and reads and writes very fast, so you can safely use it without having to worry about harming the speed of Redis by turning on slow log.

Set up and view SLOWLOG

The server configuration has two options related to slow query logs:

Slowlog-log-slower-than: the option specifies how many microseconds (1 second equals 1000000 microseconds) command requests that take longer to execute will be logged. For example, if the value of this option is 100, then commands that take longer than 100 microseconds will be logged to the slow query log; if the value of this option is 500, then commands that take more than 500 microseconds will be logged to the slow query log, and so on.

Slowlog-max-len: the option specifies the maximum number of slow query logs that the server can save. The server saves multiple slow logs on a first-in-first-out basis: when the number of slow logs stored by the server is equal to the value of the slowlog-max-len option, the server will delete the oldest slow log before adding a new one. For example, if the server slowlog-max-len has a value of 100 and assumes that the server has stored 100 slow query logs, then if the server is going to add a new log, it must first delete the oldest log currently saved and then add the new log.

Let's take a look at an example of the slow query log feature. First, use the CONFIG_SET command to set the value of the slowlog-log-slower-than option to 0 microseconds, so that any commands executed by the Redis server will be recorded in the slow log, and then set the value of the slowlog-max-len option to 5, so that the server can only save a maximum of 5 slow logs:

Redis > CONFIG SET slowlog-log-slower-than 0OKredis > CONFIG SET slowlog-max-len 5OK

Next, we use the client to send several command requests:

Redis > SET msg "hello world" OKredis > SET number 10086OKredis > SET database "Redis" OK

Then use the SLOWLOG GET command to view the slow query log saved by the server:

Redis > SLOWLOG GET1) 1) (integer) 4 # log unique identifier (uid); 2) (integer) 1378781447 # command execution UNIX timest 3) (integer) 13 # command execution time in microseconds; 4) 1) "SET" # command and command parameters 2) "database" 3) "Redis" 2) 1) (integer) 3 2) (integer) 1378781439 3) (integer) 10 4) 1) "SET" 2) "number" 3) "10086" 3) 1) (integer) 2) (integer) 1378781436 3) (integer) 18 4) 1) "SET" 2) "msg" 3) "hello world" 4) 1) (integer) 1 2) (integer) 1378781425 3) (integer) 11 4) 1) "CONFIG" 2) "SET" 3) "slowlog-max-len" 4) "5" 5) 1) (integer) 0 2) (integer) 1378781415 3) (integer) 53 4) 1) "CONFIG" 2) "SET" 3) "slowlog-log-slower-than" 4) "0"

If we execute another SLOWLOG GET 1 command at this time, we will see that the last SLOWLOG GET command has been recorded in the slow query log, while the oldest slow query log numbered 0 has been deleted, and the number of slow query logs on the server is still 5:

Redis > SLOWLOG GET 11) 1) (integer) 52) (integer) 1378781521 3) (integer) 61 4) 1) "SLOWLOG" 2) "GET"

The unique id of the log is reset only when the Redis server is restarted, which avoids repetitive processing of the log (for example, you may want to email you every time you find a new slow query).

Use the command SLOWLOG LEN to view the number of current logs.

Note the difference between this value and slower-max-len, one is the number of current logs and the other is the maximum number of logs allowed to be logged.

Redis > SLOWLOG LEN (integer) 5 clear the log

Use the command SLOWLOG RESET to empty the slow log.

Redis > SLOWLOG RESETOK above is all the contents of this article entitled "how to use the Redis slow query Log". Thank you for reading! I believe you will gain a lot after reading this article. The editor will update different knowledge for you every day. If you want to learn more knowledge, please pay attention to the industry information channel.

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