Fixing High Server resource consumption for a WP website

On the website serbianmonitor.com it has been conducted a detailed investigation and it turned out that application executes slow queries towards its database, which eventually hogs the server. The server tries to execute slow queries while putting other processes in the queue until some memory is freed. While they are waiting however, they stack up and cause further problems. There can be many reasons for slow database queries, but the following 3 are the most common ones:

1. Large database
2. Not well written scripts
3. Large number of internal links that query the database directly.