Why should I close or keep Redis connections open?

Question

I'm using Redis in a PHP project. I use phpredis as a client. Sometimes, during long CLI-scripts, I experience PHP segmentation faults.

I've experienced before that phpredis has problems when the connection times out. As my Redis config is configured to automatically close idle connections after 300 seconds, I guess that causes the segmentation fault.

In order to be able to choose whether to increase the connection timeout or default it to 0 (which means "never timeout"), I would like to know what the possible advantages and disadvantages are?

Why should I never close a connection?
Why should I make sure connections don't stay open?

Thanks

Answer 1

Generally, opening a connection is an expensive operation so modern best practices are to keep them open. On the other hand, open connections requires resources (from the database) to manage so keeping a lot of idle connections open can also be problematic. This trade off is usually resolved via the use of connection pools.

That said, what's more interesting is why does PHP segfault. The timeout is, evidently, caused by a long running command (CLI script in your case) that blocks Redis (which is mostly single threaded) from attending to the PHP app's connections. While this is a well-known Redis behavior, I would expect PHP (event without featuring reconnect at the client library) not to s**t its pants so miserably.