PDOATTRPERSISTENT

PDOATTRPERSISTENT is a predefined constant used with the PDO (PHP Data Objects) extension in PHP. It is passed as the second argument to the PDO constructor when establishing a database connection. When this attribute is set, it instructs PDO to attempt to create a persistent database connection.

Persistent connections are pooled by the PHP process. This means that if a script connects to a database using a persistent connection, and subsequently another script on the same server connects to the same database using the same connection details and the persistent attribute, the second script can reuse the existing connection from the pool instead of establishing a new one.

The primary benefit of using persistent connections is performance. Establishing a database connection can be an expensive operation, involving network round trips and authentication. By reusing existing connections, the overhead of repeated connection establishment is eliminated, leading to faster script execution, especially in environments with high request loads.

However, persistent connections also have potential drawbacks. They can consume server resources as connections remain open even when not actively in use between requests. This can lead to resource exhaustion if not managed carefully. Additionally, changes to database schema or user permissions that occur after the connection is established might not be reflected until the connection is reset or the PHP process restarts. Therefore, persistent connections are best suited for environments where the database schema is stable and the application has a consistent connection pattern.