[MySQL] MySQL 8 新特性：全局参数持久化！

• SET PERSIST语句可以修改内存中变量的值，并且将修改后的值写?数据?录中的 mysqld-auto.cnf 中。
  
• SET PERSIST_ONLY语句不会修改内存中变量的值，只是将修改后的值写?数据?录中的 mysqld-auto.cnf 中。
  

mysql>select*fromperformance_schema.persisted_variables;
Emptyset(0.00sec)
 
mysql>showvariableslike'%max_connections%';
+------------------------+-------+
|Variable_name|Value|
+------------------------+-------+
|max_connections|151|
|mysqlx_max_connections|100|
+------------------------+-------+
2rowsinset(0.00sec)
 
mysql>setpersistmax_connections=300;
QueryOK,0rowsaffected(0.00sec)
 
mysql>select*fromperformance_schema.persisted_variables;
+-----------------+----------------+
|VARIABLE_NAME|VARIABLE_VALUE|
+-----------------+----------------+
|max_connections|300|
+-----------------+----------------+
1rowinset(0.00sec)

{
"Version":1,
"mysql_server":{
"max_connections":{
"Value":"300",
"Metadata":{
"Timestamp":1632575065787609,
"User":"root",
"Host":"localhost"
}
}
}
}

mysql>setpersistmax_connections=DEFAULT;
QueryOK,0rowsaffected(0.00sec)
 
mysql>select*fromperformance_schema.persisted_variables;
+-----------------+----------------+
|VARIABLE_NAME|VARIABLE_VALUE|
+-----------------+----------------+
|max_connections|151|
+-----------------+----------------+
1rowinset(0.00sec)

mysql>RESETPERSIST;
QueryOK,0rowsaffected(0.00sec)
 
mysql>select*fromperformance_schema.persisted_variables;
Emptyset(0.00sec)