In PDO, a connection can be made persistent using the
PDO::ATTR_PERSISTENT attribute. According to the php manual -
Persistent connections are not closed at the end of the script, but are cached and re-used when another script requests a connection using the same credentials. The persistent connection cache allows you to avoid the overhead of establishing a new connection every time a script needs to talk to a database, resulting in a faster web application.
The manual also recommends not to use persistent connection while using PDO ODBC driver, because it may hamper the ODBC Connection Pooling process.
So apparently there seems to be no drawbacks of using persistent connection in PDO, except in the last case. However., I would like to know if there is any other disadvantages of using this mechanism, i.e., a situation where this mechanism results in performance degradation or something like that.