Have you considered SQLite? PHP has support for it built-in (php-sqlite3 package in Debian) and you wouldn't have to manage a database server. Concurrent reques

Have you considered SQLite? PHP has support for it built-in (php-sqlite3 package in Debian) and you wouldn't have to manage a database server. Concurrent requests should be fine since SQLite does R/W locking and supports transactions. I can't personally comment on how well it works for websites but I have used PHP+SQLite for local ad-hoc GUI apps and it was a pretty nice experience.