Stuck pt-archiver query during purge

I am purging a table of size 1.2T using pt-archiver. In the show processlist i can see the query stuck for 650 secs in Sending data state. The query is quick when I execute independely. Any help will be appreciated. [shell]# pt-archiver --source h=localhost,D=dsm,t=subscriber_event -u XX -pXXX --where="created explain SELECT /*!40001 SQL_NO_CACHE */ id FROM dsm.subscriber_event FORCE INDEX(PRIMARY) WHERE (created SELECT /*!40001 SQL_NO_CACHE */ id FROM dsm.subscriber_event FORCE INDEX(PRIMARY) WHERE (created <= DATE_SUB(now(), interval 1 year)) AND (id < '3873802696') ORDER BY id LIMIT 10000; | 3205169561 | | 3205169562 | | 3205169563 | | 3205169564 | +------------+ 10000 rows in set (0.10 sec) Please help me finding out the exact cause.