Greyhole is at the time of writing using SQLite as the default databas database for queueing up tasks on Amahi. This is unqie to Amahi as Greyhole was originally designed to use MySQL for this task.

There are some major performance benefits to using MySQL over SQLite when writing large amounts of files. Switching can be especially useful when moving data to greyhole shares for the first time. For now there is a script you can run if you want to switch over. This script has been tested too to be safe while greyhole is working but should be used with discresion.