SQL error when generating reports

Document ID : KB000122889
Last Modified Date : 12/12/2018
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Reports showing below error when trying to generate

An error occurred!
Control(30002): Stacked Protocol Trend - In

A Unable to connect to any of the specified MySQL hosts. error was returned: at MySql.Data.MySqlClient.NativeDriver.Open() 

User-added image
NFA 9.3.8 
1 Console server on windows 2012 R2
1 Harvester on Linux
The problem was that the MySQL instance which is supposed to run on port 3307 was down. 
Found that there is a log file named NFACustomStorageEngine.log which was owned by root user. 
Changed the user for the log file to NFA user and then try to start the MySQL CSE
Successfully started NQMySQL service
Additional Information:
Also verify whether NFA poller service is running