TRUNCATE TABLE statement sometimes hangs
The reason why you experience performance degradation or stall while executing TRUNCATE TABLE is a known issue with this statement. Please refer to Bug #68184:Truncate table causes innodb  stalls. There are other bug numbers opened for prior versions as well.

You can use:

CREATE TABLE log_table_new LIKE log_table;
RENAME TABLE log_table TO log_table_old, log_table_new TO log_table;
DROP TABLE log_table_old;


It gets tricky for tables with AUTO_INCREMENT values: new table is created with an AUTO_INCREMENT value which is immediately taken in the working table. If you do no want to  use same values, you can:

ALTER TABLE log_table_new AUTO_INCREMENT=some high enough value;