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close mysql connection important?

How important is it close an mysql connection in a website and why?


Like so often, it depends.

What could happen:

  • The connection could stay open and you can run out of the maximum open connections
  • Your changes aren't committed

Depending on program language, middle ware, ...

+1  A: 

I don't know about other languages, but php closes the connection automatically on the end of script execution.

In general case, you close connection so that sql server doesn't have to wait for more commands from the website (which it won't receive, because the script has finished execution), and doesn't hit connection quota (if it has any).

+2  A: 

Every database engine has a limit on a maximum number of simultaneous connections. So if you don't close the connection, mysql can run out of available connections (default max_connections is 100). In addition, each connection you hold consumes server's resources (memory, a thread to listen, might be open filehandles).


This does NOT hold true if the only things opening connection are web apps from ONE server and they use pooled connections. In such a case, you don't risk opening more and more new connections (since every time your app needs a new one, it picks the ones available from the pool); and closing and re-opening the pool's connections just wastes resources.

However, if a script terminates abnormally, it may leave a transaction and/or locks active on the DB connection it was using. This can lock up the system if a critical table/row becomes wedged like this. Closing the connection would clean up these leftover locks/transactions.
Marc B
+1  A: 

PHP will automatically close the connection when the script exits, so I wouldn't normally worry about it too much.

The database server will have a finite possible number of simultaneous connections, so on a very heavily loaded site it might help to free the connection as soon as possible.


Because there is a limit to the number of sockets connections that can be opened.


If you don't properly close your connections you could get into trouble. You will probably receive Too many connections errors. See here


I'm not THE programmer, but I think it's better to close it as soon as you don't need it. Say, for example, you open the connection, execute the query and for some reason, working with that data takes a long time. If you haven't closed the connection yet (and the program/script hasn't ended either, so it hasn't automatically closed the connection -if there's such a chance), there will be a busy resource which is doing nothing in MySQL. A connection is open but you're not using it, that means another client using the service probably will see the great "Error: Can't connect to the DB" message. So, in my humble opinion, it's better to connect to the DB, gather the requiered data, close the connection and then process the data. That at least will leave one available connection to future clients (which is really important if you have high-concurrency apps).

Nevertheless, that kind of behaviour depends on the programming language but all I know can retrieve data to a variable and it's connection-independent, so I can just close it and keep working with the data while leaving the connection available to another client.