redis driver _get_lock set lock_key problem

There's a few things you can do to reduce this, they won't fix it completely but it will help.

1) Upgrade to the latest versions of Redis and phpredis.
2) Call session_write_close() in every request as soon as you're done writing session data. You can still read session data after you call this just not write it.

Newer versions of phpredis seem to show this message less frequently. There's quite a few threads on here about it and I don't think anyone's definitively figured out what the cause is.