The default on python 3.8 is for max_workers is significantly
lower than the default on python 3.7 which means we can get starved
for workers.
To determine a reasonable maximum, the maximum was increased to large
number on 5 production instances.
The number of worker threads created during startup that were
needed to avoid waiting for a thread:
HOU 1 - 71
HOU 2 - 48
OGG 1 - 60
OGG 2 - 68
OGG 3 - 64
This lead to a selection of 64 as it was reliable in all cases
and did not have a significant memory impact
