Making PHP-to-MySQL Connections Persistent

I have been seeing these bursts of traffic, mainly from spambot morons, that have suddenly been crushing my server. The main cause: excessive database connections.
This was quickly remedied today when I changed all of the mysql_connect statements to mysql_pconnect statements. This allows PHP to use an existing connection to the MySQL database to serve requests from the same Apache child process.
Now the truly geeky among you are going “DOH! Wadda ya mean you were opening a new connection for every request?”. Well, believe it or not, I will bet you dollars to doughnuts that your blog app doesn’t persist database connections. Not a big deal if your database is on the same machine, and you are using local named pipes to make requests. However, if that database is located on another machine, if you do a netstat, you will see a large number of connection on port 3306.
Persisting database connections is particularly important for large hosted services. A great deal of TCP overhead, and kernel space memory can be saved by simply not letting the Web server saturate the database with individual database connections for every page request.
Without persistent database connections, eventually the TCP queue will be full of database connections and no one will be able to connect to the server, or they will get a lovely “can’t connect to database error”.


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