how to understand “can't connect” mysql error messages?

Question

I have the following error message:

SQLSTATE[HY000] [2003] Can\'t connect to MySQL server on \'192.168.50.45\' (4)

How would I

Answer 1

FWIW, having spent around 2-3 months looking into this in a variety of ways, we have come to the conclusion that (at least for us), the (4) error happen when the network is too full of data for the connection to complete in a sane amount of time. from our investigations, the (4) occurs midway through the handshaking process. You can see this in a unix environment by using 'netem' to fake network congestion.

The quick solution is to up the connection timeout parameter. This will hide any (4) error, but may not be the solution to the issue. The real solution is to see what is happeneing at the DB end at the time. If you are processing a lot of data when this happens, it may be a good ideas to see if you can split this into smaller chunks, or even pas the processing to a different server, if you have that luxury.