Four logs of MySQL server layer

One 、MySQL Server Introduction to layer log

When one MySQL Server Client Initiate a connection request , stay MySQL What the backend has to do ：

MySQL The journal is in MySQL server Generated on , No matter which storage engine you change , These logs are needed , Include ：

• Error log ： Record mysqld During the operation of the service cordump、error、exception etc.

• Query log ： Record MySQL Server All that you've received SQL. Due to the of online projects SQL That's too much , Open query log IO Too much leads to MySQL inefficiency , We It usually doesn't open , Only start when debugging . For example, by looking at sql Discover hotspot data and cache it ：
  

• Binary log ： Record data changes （insert、update、delete、alter …）, It's very important , Can be used for Data recovery , Master slave copy . Master-slave replication technology depends on log_bin, All changes to the main library are recorded in log_bin in , From the library from binlog Read all operations of the main library , Do it again .
  

• Slow query log ： Records some instances where the execution time exceeds the specified value SQL sentence , Available for developers to analyze SQL, So as to optimize

MySQL There are many global variables defined in to record settings or states , Check is show variables（ Global variables ） perhaps show status（ state ）. View log related variables ：

Two 、 Profile parameters

open my.ini, Add the above parameters to the back , Restart after saving mysql Just the service .

adopt set Method can only affect the current session, If you want to The configuration is permanently valid , It needs to be set on the configuration file , And then restart MySQL service , It can take effect forever

linux Next restart mysqld Commands for services ：sudo service mysqld restart

Let's look at the configuration file /etc/mysql/my.cnf

• give log-error The path is open log-error, If not custom log-error The path of , Default in data_dir
• In the open log-bin=mysql-bin At the same time, add server-id=1( At present MySQL Server The identity of the ）, Otherwise, in the linux root Next sudo service mysqld restart The service cannot be restarted
• Set expiration time expire_log_days, Because one day the disk will be full of this log , Causes the server to become inoperable , After the set time is exceeded, the log file will be deleted

3、 ... and 、 Error log

Four 、 Binary log

Binary log (BINLOG) It records all the DDL( Data definition language ) and DML( Data manipulation language ) sentence , But it does not include data query statements . Statement to “ event ” Form preservation of , It describes the data change process . This log plays an extremely important role in data recovery in case of disaster .

Two important scenes ： Master slave copy 、 Data recovery .

see binlog：show binary logs

Binary content cannot be viewed directly , Because it doesn't record plaintext , Because it's a little unsafe to record plaintext , After all, it is the details of database table changes , Unlike slow queries, logs are recorded in clear text .

binlog Default in MySQL Of data_dir Next

1. demonstration binlog Record changes

Let's refresh , Make a new one binlog

Use school Database based user Table ：

perform insert and update operation

Look again binlog

We found that the log filesize It's different from just now , Be sure to record the data change operation we just did

If we go straight cat Log view , You will find that it is not in clear text , Unable to view directly

adopt mysqlbinlog Tools (mysql Native tools ) Mind parsing a large number of binlog Log files :

mysqlbinlog --no-defaults --database=school --base64-output=decode-rows -v --start-datetime='2022-03-01 00:00:00' --stop-datetime='2022-03-31 00:00:00' mysql-bin.000001 | more

• database： Specify to view changes to a library
• base64-output：binlog Decoding method
• start-datetime & stop-datetime： Specify to view changes in a certain period of time , If you don't write, view all changes
• mysql-bin.000001： View the binary log file

Let's take a look at what just changed binlog：

• @1、@2、@3、@4： Represents the name of the database table 4 A field
• server id： It means that we are my.cnf Set in the id, Used to identify the current MySQL The identity of the
• at 565、at679： It refers to the current event in binlog The location of the record , Use when recovering data .

2. demonstration binlog Data recovery

establish mytest database , Create inside user Table and add data

If someone deletes the library now

At this time mytest All tables and data in the library are gone , However, these operations are recorded in the binary log binlog Inside

In theory , It can be downloaded from binlog Recover the lost data . Because the recovery process is also the modification of data , Therefore, the logs generated during the recovery process should also be recorded in binlog in , So in order to prevent us from not knowing where to end the data recovery process , Or we can't tell which binary logs we need to recover and which are newly generated in the recovery , This requires us Appoint binlog Recovery interval

We now know , We build a library 、 Build table 、 The operations of inserting data are recorded in mysql-bin.00003 In file

Let's refresh now , Make a new one binlog, This allows our next data recovery operations to be recorded in mysql-bin.00004 In file , Instead of adding to mysql-bin.00003

So let's look at mysql-bin.00003, Find the interval that needs to be recovered



from mysql-bin.000003 Take out all the operations in the interval , Through the pipe MySQL shell On the implementation

View the current library , You can see mytest Has recovered

Then check the table and data

In this way, all the data will be restored .

We can not only pass binlog The location of the record , Get the interval that needs to be recovered , It can also be done through binlog Record the time to get the interval to be recovered , Parameter is ：start-datetime、stop-datetime

Pay attention to data recovery in actual use ： Because of configuration bin-log It is also configured mysql-bin, Also configured expire_logs_days（ The expiration time of the log ）, How to recover the data before the expiration time ？

mysql The recovery of data depends on Data backup and binlog Data recovery . The expired log data will be backed up , No expired data can be passed directly through binlog recovery . Generally, data backup is to backup data to sql In the script file , For example, save in ~/data.sql in , And then in mysql with source ~/data.sql perform , Or if it's in linux Of shell Pipes can be used inside ：cat ~/data.mysql|mysql -u root -p, We can restore the data we backed up before to mysql In the library table of .

5、 ... and 、 Slow query log

Slow query log details