use connection pooling for database queries

[dhach]

To avoid possible, future performance bottlenecks, the application should use connection pooling for database queries.

Currently, every API call results in a completely new database connection, query and subsequent connection closure, which significantly slows down execution time of queries and resulsts in increased server load.

This can be avoided by using connection pooling:
Keep a configurable amount of connections to the database open and use these to execute the queries necessary to serve API calls.

Such a change in application design would also enable the application to terminate if the database connection is lost and cannot be re-established.