You may see queries stuck in the MySQL process list with the "Waiting for table level lock" state.
MySQL only uses row-level locking in InnoDB tables. Other storage engines use table-level locks, as documented at:
Due to this, MyISAM tables with write-heavy workloads can experience high lock contention.
The MyISAM tables can be converted to InnoDB tables which support row-level locking. This should be performed by a qualified System or Database Administrator. This can be done with the following commands, replacing DATABASE_NAME and TABLE_NAME as appropriate.
1) Ensure that backups exist for the table prior to converting.
mysqldump DATABASE_NAME TABLE_NAME > TABLE_NAME.sql
2) Convert the table to InnoDB
mysql -e "ALTER TABLE DATABASE_NAME.TABLE_NAME ENGINE=InnoDB"