Merge pull request #13400 from connection-reset/concurrent-sql

Run queries for sql data sources for panels with multiple queries concurrently
Also make max open connections, max idle connections and max connection 
lifetime configurable in the data source settings

docs/sources/features/datasources/mysql.md

@@ -35,6 +35,9 @@ Name | Description
 *Database* | Name of your MySQL database.
 *User* | Database user's login/username
 *Password* | Database user's password
+*Max open* | The maximum number of open connections to the database, default `unlimited` (Grafana v5.4+).
+*Max idle* | The maximum number of connections in the idle connection pool, default `2` (Grafana v5.4+).
+*Max lifetime* | The maximum amount of time in seconds a connection may be reused, default `14400`/4 hours. This should always be lower than configured [wait_timeout](https://dev.mysql.com/doc/refman/8.0/en/server-system-variables.html#sysvar_wait_timeout) in MySQL (Grafana v5.4+).
 
 ### Min time interval
 
@@ -316,4 +319,8 @@ datasources:
     database: grafana
     user: grafana
     password: password
+    jsonData:
+      maxOpenConns: 0         # Grafana v5.4+
+      maxIdleConns: 2         # Grafana v5.4+
+      connMaxLifetime: 14400  # Grafana v5.4+
 ```