threads in cleaning up mode

Hi to all,

For many days, I am struggling with the problem of  increasing history list
length on mysql 5.6.29. Application that this server is running IOT based.
Also, this server has so many threads running in sleeping mode. SHOW ENGINE
INNODB STATUS shows all these threads in *cleaning up* mode.
I tried all the options to reduce history list length. But it is constantly
increasing.
Below are the current settings of purge related threads:

innodb_max_purge_lag       | 1000000 |
| innodb_max_purge_lag_delay | 0       |
| innodb_purge_batch_size    | 1       |
| innodb_purge_threads       | 8       |

Also, please let me know that whether cleaning up mode of threads and
history list length are correlated.

Anty help?


Best Regards,
Geetanjali Mehra
Senior Database Administrator