Switching to use INSERT DELAYED, which it should be, for rpl_insert.

CREATE TABLE t1 (id INT, name VARCHAR(64));

let $query = "INSERT INTO t1 VALUES (1, 'Dr. No'), (2, 'From Russia With Love'), (3, 'Goldfinger'), (4, 'Thunderball'), (5, 'You Only Live Twice')";

let $query = "INSERT DELAYED INTO t1 VALUES (1, 'Dr. No'), (2, 'From Russia With Love'), (3, 'Goldfinger'), (4, 'Thunderball'), (5, 'You Only Live Twice')";

--exec $MYSQL_SLAP --silent --concurrency=20 --iterations=200 --query=$query --delimiter=";"

SELECT COUNT(*) FROM mysqlslap.t1;