History list length 2051529
Main thread process no. 9701, id 1111792528, state: sleeping
Oh Innodb purge thread isn't running, and there is no change in "history length".
Note: Purge thread never progresses when the main thread is in a 'sleep' state.
Related BUG 13847885. Quoting:
Deleting a huge amount of data from
InnoDBtables within a short time could cause the purge operation that removes delete-marked records to stall. This issue could result in unnecessary disk space use, but does not cause any problems with data integrity. If this issue causes a disk space shortage, restart the server to work around it. This issue is only likely to occur on 32-bit platforms
Bug fixed in 5.0.97, 5.1.63, 5.5.23
Solution: Restart MySQL and upgrade MySQL version