MariaDB filling up /tmp folder

I have a large forum database with 3 million posts. It was on a VPS that used MySQL and I didn't have any problems. Recently I moved it to a VPS that has MariaDB pre installed. Immediately I am noticing a couple times a day the /tmp folder (which is 4GB) is becoming filled 100% (causing the server to fail) when ever someone does forum searches. 1) Is it possible to specify an alternate /tmp folder for MariaDB? 2) Could this be avoided by providing more RAM to MariaDB so that it didn't have to write to the /tmp folder?