A common story: You’ve got some connection, either it’s busy running something it shouldn’t be, it’s in Sleep but holding some important lock, or you just don’t know why it’s connected to your database server in the first place. You see it in your SHOW PROCESSLIST like so:
mysql> show processlist G
*************************** 1. row ***************************
Id: 5979887
User: root
Host: localhost:55997
db: NULL
Command: Sleep
Time: 475
State:
Info: NULL
How do you find that client, especially if it’s on another host? MySQL is providing you all the information you need above: localhost:55997. Of course localhost is the host or IP address, and 55997 is the source port of the socket; the port number (usually randomly assigned) on the far end of the socket, from the MySQL server’s perspective. You can turn that number into something useful—the PID and user—, by running the following command on the host that made the connection:
# lsof -nPi :55997 COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME mysqld 5026 mysql 1654u IPv4 303329996 TCP 127.0.0.1:3306->127.0.0.1:55997 (ESTABLISHED) mysql 9146 jcole 3u IPv4 303329995 TCP 127.0.0.1:55997->127.0.0.1:3306 (ESTABLISHED)
(Note that here you can see both sides of the socket, since I’m running these commands on localhost. Disregard the first entry, as it’s the half of the connection owned by the MySQL server.)
You can then find out the full command-line of the process with ps:
# ps -fp 9146 UID PID PPID C STIME TTY TIME CMD jcole 9146 8740 0 12:53 pts/3 00:00:00 mysql -h 127.0.0.1 -u root -p
And see what it’s doing with strace (waiting on a read of stdin in this dumb test):
# strace -p 9146 Process 9146 attached - interrupt to quit read(0, <unfinished ...> Process 9146 detached
I hope that’s helpful! It’s a pretty common debugging trick for me.
