Database only supports up to ~20 concurrent transactions

[Derppening]

Issue description

When there are more than around 15 concurrent users conducting a transaction, additional users are unable to start a new transaction and the server does not respond.

Steps to reproduce this issue

1. Login to the server using valid credentials
2. Initiate a transaction using the token from the previous step
3. Repeat until the message com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Could not create connection to database server. Attempted reconnect 3 times. Giving up. is shown in the server console.

What's the expected result?

• The API returns either 200 OK or uses other code (e.g. 500 Internal Server Error) to indicate an error has occurred

What's the actual result?

• The client receives no response

[comp4111ta]

It is required to perform concurrent transactions in Phase 2