MySQL

MySQL (owned by Oracle) is the deeply respected, incredibly ubiquitous, absolute mathematical workhorse of the "Internet Infrastructure" market. In the 2000s, it mathematically powered the LAMP stack (Linux, Apache, MySQL, PHP), physically building the modern web. From WordPress blogs to the early versions of Facebook and Twitter, MySQL provided terrifyingly fast, simple, open-source relational reading capabilities that allowed the internet to scale massively for free. Its absolute biggest differentiator is "The InnoDB Storage Engine." While PostgreSQL focuses on massive analytical complexity, MySQL is mathematically obsessed with raw, terrifyingly fast Read/Write web transactions. The InnoDB engine mathematically handles row-level locking and foreign key constraints with incredible efficiency. When a user clicks "Like" on a Facebook post, or "Add to Cart" on a massive E-Commerce site, MySQL executes that tiny mathematical transaction faster than almost anything on earth. Because it targets massive web scale, its "Master-Slave Replication" is legendary. A news website has 1 database but 1 million readers. The database crashes under the load. MySQL mathematically solves this. It creates one "Master" database that accepts new articles (Writes). It then mathematically replicates that data to 50 "Slave" databases. All 1 million readers are mathematically routed to the Slave databases, completely separating the read traffic from the write traffic.