PostgreSQL

A customer clicks Pay. Your server charges the card, and then the connection drops before the response reaches the browser. The client cannot tell whether the c…

PostgreSQL never overwrites a row in place. An UPDATE writes a new version of the row and marks the old one as replaced; a DELETE only marks the row. That desig…

Two support agents both open the same account balance, both see $100, both independently process a $50 withdrawal, and the balance ends up at $50 instead of $0 …