Our current History Store create configuration string is:

"key_format="IuQQ",value_format="QQQu",block_compressor="WT_HS_COMPRESSOR                                     ",leaf_value_max=64MB,prefix_compression=false"

We should update the configuration to make it very unlikely that we'll ever use overflow keys in the history store. Probably by setting leaf_key_max and internal_key_max to the same value as leaf_value_max.

The default value is 1/10th of a page split size. The default page size is 4KB meaning that the overflow size is about 400 bytes. MongoDB could definitely be triggering that with indexes at the moment.