Master database server
From Wikitech
The master database server is the primary server running mySQL. The slave database servers replicate data from this central point. If the master database server fails, then a slave can be promoted to be a new master without a horrendous amount of work. See Master switch for how to do this.
To determine which host is the master for the enwiki cluster, you can run
echo 'echo wfGetLB()->getServerName(0);' | php /home/wikipedia/common/php/maintenance/eval.php enwiki
There used to be a command /home/wikipedia/bin/master which relied on /home/wikipedia/common/php-1.5/db.php, but that method doesn't seem to work any more.
