Important link

https://medium.com/@XiaohanZeng/i-interviewed-at-five-top-companies-in-silicon-valley-in-five-days-and-luckily-got-five-job-offers-25178cf74e0f

Transaction Management https://vladmihalcea.com/a-beginners-guide-to-database-locking-and-the-lost-update-phenomena/

Thread Pool https://www.javacodegeeks.com/2016/12/implement-thread-pool-java.html