Redis learning notes - slow query analysis

Slow query logs help developers locate slow operations in the system , Slow query is the execution time of each command calculated by the system before and after the command execution , When the preset threshold is exceeded , This command will be the relevant information （ for example ： Time of occurrence , Time consuming , Command details ） recorded ,Redis Provides similar functionality

The four execution steps of the client request

1. dispatch orders ——2. Queued for execution ——3. Carry out orders ——4. Return results

Slow query only counts steps 3 This step of executing the command , Therefore, no slow query does not mean that the client does not timeout

Configuration parameters for slow queries

stay redis.conf There are two configuration items in the configuration file ：slowlog-log-slower-than and slowlog-max-len

slowlog-log-slower-than Indicates a preset threshold , The default is 10000 Microsecond （1 second =1000 millisecond =1000000 Microsecond ）, If a command takes longer than 10000 Microseconds will be recorded in the slow query log
If slowlog-log-slower-than Set to 0 All the commands will be recorded , Set to less than 0 No command will be recorded

slowlog-max-len：Redis A list is used to store slow query logs , This configuration is the maximum length of the list , The default is 128 strip , If more than 128 The first inserted data will be deleted

If you want to modify the configuration, you can directly go to redis Modify the client , With slowlog-max-len For example

127.0.0.1:6379> config set slowlog-max-len 512
OK
127.0.0.1:6379> config rewrite
OK

When viewing the configuration file , Find out slowlog-max-len The configuration has been modified to 512 了

Get slow query log

Although the slow query log is stored in Redis In the memory list , however Redis There are no keys to expose this list , But through a set of commands to achieve the slow query log access and management .

slowlog get [n]

Query two slow query records , Here [n] It is optional , If you do not fill in all the , If you fill in, you will query the specified number of items

127.0.0.1:6379> slowlog get "2"
1) 1) (integer) 12
   2) (integer) 1552899968
   3) (integer) 1000502
   4) 1) "migrate"
      2) "127.0.0.1"
      3) "6379"
      4) "a"
      5) "1"
      6) "1000"
      7) "copy"
   5) "127.0.0.1:35730"
   6) ""
2) 1) (integer) 11
   2) (integer) 1552899943
   3) (integer) 1000909
   4) 1) "migrate"
      2) "127.0.0.1"
      3) "6379"
      4) "a"
      5) "0"
      6) "1000"
      7) "copy"
   5) "127.0.0.1:35730"
   6) ""

Four main parameters

• Slow query log identification id
• Occurrence timestamp
• The command takes time
• Execute commands and parameters

Get the length of the slow query list

slowlog len

The current is 13 Slow query

127.0.0.1:6379> slowlog len
(integer) 13

Clear slow query list

slowlog reset

Clear the current slow query list

127.0.0.1:6379> slowlog len
(integer) 13
127.0.0.1:6379> slowlog reset
OK
127.0.0.1:6379> slowlog len
(integer) 0