07 Aug 2011

Fixing Mac Shutdown Delays

or, How MySQL is broken on OS X

Ever since I saw James Edward Grey II point out the delay at shutdown caused by having MySQL installed on OS X, it has bugged me. A lot. I even spent a few hours trying to figure out what was going on back then, but to no avail. The only thing I was able to figure out at the time was that running launchctl unload com.mysql.mysqld.plist always took 20 seconds.

This last week, however, I installed MySQL 5.5 on a new MacBook Air. The first thing I discovered is that it is deeply broken. Not only is the path to the shared library incomplete, the provided OS X StartupItem doesn't work.

Since the startup item was broken, I resolved to create a plist that would allow launchd to control MySQL. While I was creating and testing that plist, I discovered that mysqld completely ignores interrupts, and will happily run forever while you press ⌃C to no avail. The only way to tell the server process to stop is to send it a SIGTERM, via kill or what have you. As I made that discovery, I suddenly developed a hunch that the shutdown delay was caused by the mysqld process refusing to shut down when interrupted.

After a bit of digging through the search results for launchd 20 seconds, I discovered the launchd.plist man page. On that page, I learned about a completely new (to me) option: ExitTimeOut.

ExitTimeOut <integer>
The amount of time launchd waits before sending a SIGKILL signal. The default value is 20 seconds. The value zero is interpreted as infinity.

The mention of a 20 second default stood out like a red flag to me, so I tried adding an entry to the MySQL plist that changed ExitTimeOut to one second. As soon as I did that, launchctl unload com.mysql.mysqld.plist took only one second to run. With great excitement, I tested out restarting my computer, and discovered that that single change completely resolved the long delays that had been irritating me.

Here is the complete code for the plist, located at /Library/LaunchDaemons/com.mysql.mysqld.plist.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN"
<plist version="1.0">

If you want to load it without restarting your machine, use the command sudo launchctl load /Library/LaunchDaemons/com.mysql.mysqld.plist.