boto3.session.Session constructor causes significant performance degradation

[timothy-godfrey]

I encountered a significant performance drop when upgrading from version 0.1.4 to 0.2.1, and the offending change was calling the session constructor at line 12 of database_wrapper.py

I found that by reverting that change only the performance impact was reversed. Reading the commit message for the change I saw that it was implemented to prevent multi-threading access problems to the boto3 client, so I recognise there are reasons for the change, but the performance impact with the current solution is quite significant.