Here was as good question I found on stackexchange:
How do you empty the buffers and cache on a Linux system?
http://unix.stackexchange.com/questions/87908/how-do-you-empty-the-buffers-and-cache-on-a-linux-system
If I don't flush out the file system cache when restarting MySQL on prod severs, I frequently get timeouts when restarting. The servers I typically work with have about 250GB of RAM, 40 CPU. Something like this will happen where I have to kill the start command or it just doesn't start.
# service mysql status
MySQL (Percona Server) running (182654) [ OK ]
# service mysql restart
Shutting down MySQL (Percona Server).......................[ OK ]......................................
Starting MySQL (Percona Server).......................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................^C
However, if I run this:
sync && echo 3 > /proc/sys/vm/drop_caches
MySQL starts up quick.
Starting MySQL (Percona Server)............................[ OK ]....................
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