Too many connections Exception

Question

I try to run SELECT on a table in MySql and i get this error:

Server Error in '/MyApp' Application.
Too many connections
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: MySql.Data.MySqlClient.MySqlException: Too many connections

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:

[MySqlException (0x80004005): Too many connections] MySql.Data.MySqlClient.MySqlStream.ReadPacket() +517 MySql.Data.MySqlClient.NativeDriver.Open() +702 MySql.Data.MySqlClient.Driver.Open() +245 MySql.Data.MySqlClient.Driver.Create(MySqlConnectionStringBuilder settings) +297 MySql.Data.MySqlClient.MySqlPool.CreateNewPooledConnection() +18 MySql.Data.MySqlClient.MySqlPool.GetPooledConnection() +403 MySql.Data.MySqlClient.MySqlPool.TryToGetDriver() +228 MySql.Data.MySqlClient.MySqlPool.GetConnection() +106 MySql.Data.MySqlClient.MySqlConnection.Open() +1468

Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.1

I run it on iis with .net and C#. Any idea how i can fix this problem?

EDIT

I add some code from my server:

This is for example how i make select:

MySqlDataReader msdr;

MySqlConnection connect = new MySqlConnection(connectionStringMySql);
MySqlCommand cmd = new MySqlCommand();

string commandLine = "SELECT * FROM Table WHERE active=1";

commandLine = commandLine.Remove(commandLine.Length - 3);
cmd.CommandText = commandLine;

cmd.Connection = connect;
cmd.Connection.Open();

msdr = cmd.ExecuteReader();

while (msdr.Read())
{
    //Read data
}
msdr.Close();
cmd.Connection.Close(); 

This is how I Delete:

MySqlConnection connect = new MySqlConnection(connectionStringMySql);
MySqlCommand cmd = new MySqlCommand();

cmd.Connection = connect;
cmd.Connection.Open();

string commandLine = @"DELETE FROM Table WHERE id=@id;";

cmd.CommandText = commandLine;

cmd.Parameters.AddWithValue("@id", slotId);

cmd.ExecuteNonQuery();
cmd.Connection.Close();

This is how I insert:

MySqlConnection connect = new MySqlConnection(connectionStringMySql);
MySqlCommand cmd = new MySqlCommand();

cmd.Connection = connect;
cmd.Connection.Open();

string commandLine = @"INSERT INTO Table (id, weekday, start, end) VALUES" +
    "(@ id, @weekday, @start, @end);";

cmd.CommandText = commandLine;

cmd.Parameters.AddWithValue("@ id", item.babysitterid);
cmd.Parameters.AddWithValue("@weekday", item.weekday);
cmd.Parameters.AddWithValue("@start", new TimeSpan(item.starthour, item.startmin, 0));
cmd.Parameters.AddWithValue("@end", new TimeSpan(item.endhour, item.endmin, 0));

cmd.ExecuteNonQuery();
long id = cmd.LastInsertedId;
cmd.Connection.Close();
return id;

Answer 1

Open up the Admin page on your (local) MySql monitor and observe to see if the number of connection grows with time. If this is unexpected behaviour, then you may have unclosed connection objects in your code (see comment from Steve below your question). If this is not unexpected ie you know that your app will generate and hold a lot of connections, then you may need to change the setting in MySQL

https://dev.mysql.com/doc/refman/5.5/en/too-many-connections.html

by adjusting max_connections :

https://dev.mysql.com/doc/refman/5.5/en/server-system-variables.html#sysvar_max_connections

UPDATE: if you don't expect and don't need so many open connections, and want to make sure you haven't overlooked any close() statements, then good practice is to employ the using construction around objects implementing IDisposable , such as connections, to make sure that they are closed as soon as possible, allowing the garbage collector to clean up objects no longer in use.

Answer 2

I don't think adjusting max connections is the right solution until it's been identified what the problem is. It could add more strain on the server / hide the actual issue.

I would make sure you're closing connections and disposing implicitly by wrapping MySqlConnection and commands in using statements.

Can you post up some code as to how you're communicating with the DB.

Also is this server a local instance?