Why is Mysql clogging up memory?

Question

MySQL

There is a server on centos with Mysql 5.5. 3.5GHz 4GB RAM 4 cores.
memory consumption 300MB. Periodically, the server crashes due to lack of memory. There is a request that hangs MySql, the rest of the requests queue up and the memory is completely consumed in a few minutes. The query that hangs MySql is then executed without any problems. The operability is restored only by rebooting the server, tk. no commands are run due to lack of memory. Tell me how to treat?

Answer 1

Find SELECT * FROM _ JOIN __ JOIN ___ ...and fix.