仅当从代码调用时，极其缓慢的mysql连接建立

Question

I am currently trying to do something that should be simple and straight-forward - connect to a database server, run a query, see if I get anything back and if so send it back to the user. This is the code I'm using to do it:

MySqlDataReader reader = MySqlHeaper.ExecuteReader(connectionString, $"SELECT * FROM table WHERE insertDateTime > '{DateTime.Now.AddSeconds(-1800).ToString("yyyy-MM-ddTHH:mm:ss")}'";

I have also tried this with a MySqlCommand and MySqlConnection object pair, and either way the result is the same - it takes approximately 7100ms to connect to the MySql server. I know that sounds like a problem that should be on ServerFault, but my testing tells me otherwise. When I use the command line MySql client to connect to my database server using exactly the same credentials and run exactly the same query I get my connection established and my data back in nothing flat. I don't know at this stage if it's a server setting or not, but here's what I've tried so far:

• Rebooting the server
• Restarting the MySQL server
• Setting the skip_name_resolve setting to 1 in order to prevent reverse name lookups on connect
• Using alternative means of querying the server (mysql command line client and MySQL Workbench)
• Opening all AWS IAM permissions on the RDS instance to allow everything from the server

Nothing seems to be making any difference, so I'm at a loss to explain this terrible performance. It's also only happening when I open the connection. Running queries, inserts, what have you is lightning fast. Any suggestions anyone might have would be most helpful.

Answer 1

I would not expect IAM permissions to have any impact on performance. I would expect them to be either successful or not successful.

I would execute some diagnostic protocols to get more information.

1) Try a subsequent query, to see if it is an issue with the stack being initialized. Are subsequent queries faster? 2) Try a query that is just an identity query. Something that doesn't require any sort of IO. 3) Try a query from a different platform (maybe a scripting language like ruby or php)

Once you answer those it should help you narrow it down.

Answer 2

This is most likely caused by Connector/NET executing a slow WMI query to query connection attributes when opening the connection; this is logged as MySQL bug 80030 .

As far as I know, this isn't fixed in newer versions of the driver, but you can work around it by switching to MySqlConnector , an OSS MySQL ADO.NET library.