the goal is simple, but rather unusual. I wrote a database auto-repair script (as one of the tables keeps crashing from time to time, probably due to very large amounts being inserted and deleted constantly), and I want to test it. The problem is, that I need to crash a table on purpose, and I have no idea how. Any suggestions?
You can certainly make a MyISAM table look crashed by truncating the .MYI file to 4k (Assuming it was bigger than 4k). Then do a FLUSH TABLE, followed by a query which needs to use an index.
If the tables are crashing spontaneously, then either
MyISAM tables should not crash spontaneously, but you can expect them to crash following an unclean shutdown. Unclean shutdowns should not happen very often, if they are, it is an operational problem. Ask your operations engineers what's going on. It is normally clear what's happened from reviewing the mysql server error log.