1. Slow Query Log Overview

1. Introduction:
Redis's slow query log is responsible for logging over the query operation that exceeds the specified execution time.This execution time does not include I / O operations (for example, communication between the server and the client, send a response message, etc.)It is only the time to execute the command actually need to consume (only at the stage of command execution, Redis will block the thread, and other requests cannot be handled).
2. Command execution process
1) Client send command
2) The REDIS server receives the command, queue the command
3) The command in the queue is executed.Slow query only the time to step 3)So there is no slow query does not mean that the client has no timeout problem.
4) Return the result

2. Two configuration parameters for slow query

1. Slow query log has two configuration parameters:
1）slowlog-log-slower-thanThe parameter is used to specify the upper limit value of the execution time (in microseconds), and the redis records the execution time exceeds the query operation of this upper limit. Note: If this parameter is set to a negative number, the slow query log is disabled; if this parameter is set to zero, each command will be enforced.
2）slowlog-max-lenThe parameter is used to specify the maximum length of the slow query log. The minimum value of this parameter is zero. When Redis records a new command into a slow query log, if the slow query log has reached the maximum length, the redis will remove the oldest command log from the log queue, so that the new command log is spatially.

2. You can configure the above two parameters in the redis.conf file, or you can configure the Config Get and Config Set commands when REDIS runtime, and then use config reference to the local configuration file.

Example:
config set slowlog-log-slower-than 20000  # This unit is microseconds, that is, 20ms
config set slowlog-max-len 1000
config rewrite

2. Read the slow query log, get the length of the slow log list, slow query log reset

Get a slow query log

slowlog get [n]

Get the current length of the list of slow query logs

Slow query log reset

You can use the Slowlog Reset command to reset the slow query log. Once deleted, the previously recorded slow query log will be permanently lost.

3. Slow log output format

The output format of the slow query log is shown below:



The unique identifier of the log entry can be used to avoid multiple repetitions of the same slow query log entries (for example, you may use a script, whenever a new slow query log entry is generated, you will send you a alarm message) . (This identifier will never be reset during the run of the REDIS server, and will only be reset when the server is restarted.)

4. Slow log query suggestion

Supplement:
1.Redis slow query because the command queuing mechanism will cause other command levels, so when the client requests timeout, you need to check if the time point has a corresponding slow query.

5. Monitor

Monitor principle

By executing the Monitor command, the client can turn itself into a monitor (server maintenance oneMonitor chain tableEach time you receive the client command, send command information to the monitor, receive and print the information requested by the server currently processed in real time:

Monitor Disadvantages (executing Monitor will also cause Redis Oom?)