We're seeing some performance gains if we disable session locking in Redis. We haven't found any issues with doing this in our testing, but wanted to see if anyone has tried that and if they have run into any issues or if anyone would advise against doing this for any reason.
We have disabled sessions on our live site and haven't run into any issues.
We reenabled session locking because it caused a rare issue with PayPal checkouts. We ended up writing a module to disable session locking for specific urls for the custom section of our site where it was a bottleneck and not necessary.
We recently saw issues where customers could not add to cart. The setting had been enabled for many months, but starting showing this behavior only two days ago. There must have been another contributing factor. I have high confidence that this was the issue though.
On add to cart, the page would show no change and no errors. The cart would never have items added.
The issue was that a new quote was being generated after adding to the cart because a new session was started. The behavior was not consistent, but very repeatable in testing.
Enabling session locking fixed this behavior entirely. We are enabling the setting again across projects and looking into other fixes to the performance issues caused by Redis locks.