In PHP, are there multiple connections to the database server when web servers serve multiple requests concurrently at the same time?

For example, assume I have a script that read/update/delete directly (without caching) data from the database (MySQL)
If there are n concurrent requests that execute this script at that time, there are also n connections to the database at that time, am I right?

Thanks in advance

In PHP, database connections are resources. Resources are not shared between requests. For example, you can't open a file handle in one PHP request and use that file handle in a different PHP request. Resources are closed automatically at the end of the request.

Each request that needs to read or write to the database opens its own database connection. If multiple requests are running concurrently, then the database will likely have multiple connections.

There are exceptions: a PHP script doesn't necessarily open a database connection immediately as it starts, or it could close the database connection before the script finishes. Or another PHP script may not need to access the database at all, so it skips opening a database connection. You might therefore have concurrent PHP requests executing, but not all of them holding an open database connection. This depends on your code, which is the reason some of the comments above are equivocating.

That said, it is common PHP coding practice to open a database connection soon after the script starts, and to leave it open for the duration of the request, relying on PHP garbage collection to close the database connection as the script exits.

So I would say in any typical PHP application, multiple concurrent requests hold an equivalent number of concurrent database connections.

You can check by using a MySQL query tool:

• SHOW GLOBAL STATUS LIKE 'Threads_connected'; shows the current number of open client connections at the moment you run this command.

• SHOW GLOBAL STATUS LIKE 'Max_used_connections'; shows the high-water mark of connections in the past (since the last restart of MySQL Server).

• SHOW PROCESSLIST; shows details about the current connections like what SQL statement they are running (or "Sleep" if they are idle between SQL statements).