MYSQL太多连接错误不会消失

Question

I'm getting a MySQL "Too many connections" error in a C++ program running on Ubuntu Linux.

This is the code that gets the error (it's inside a method that returns the mysql error, if any):

MYSQL connect;
mysql_init(&connect);
if (!mysql_real_connect(&connect,SERVER,USER,PASSWORD,DATABASE,0,NULL,0))
{
    return mysql_error(&connect);
}

This code keeps returning the string "Too many connections."

I'm wondering if this is actually some other error. This program has been working for months before I got this error. When the error first appeared it was because I had run the program against several thousand updates/reads and so yes, it's highly likely that I used up the available connections. The problem is, I can't find a way to release them, if that's what it is.

Here is what I have tried:

• FLUSH HOSTS;
• FLUSH TABLES;
• restarting MYSQL
• rebooting the machine altogether

It has been over 12 hours since this error first appeared, so if it is the connections then nothing is being reset/released. I would have thought rebooting the machine would have released something.

Answer 1

See C.5.2.7. Too many connections.

View all MySQL connections.

 netstat -apn | grep mysql | grep -i established

Tips

• Build and return connection object only when connection pointer is null or connection to DB is unavailable.
• Use one connection pool for the entirety of the session.
• Close the connection at the end of each session and release/clean the connection pointer.
• Increase max_connections=# in /etc/mysql/my.cnf or restart MySQL with --max_connections=#

Answer 2

Make sure you close connection when you are done with them.

Consider reusing connections or connection pooling.