PostgreSQL

PostgreSQL is an open-source relational database with a process-per-connection model: when a client connects, the server forks a dedicated backend to handle it. Backends share access to a large in-memory cache called the shared buffer pool, sized via shared_buffers. The pool stores recently-read 8 KB data pages (PostgreSQL's on-disk unit, distinct from a Linux memory page) so subsequent reads avoid disk.

When a backend needs a data page that isn't in the buffer pool, it calls StrategyGetBuffer to pick a slot — either an empty one or a victim to evict. That selection is protected by a single global spinlock. The design assumes the critical section is tens of nanoseconds and the holder is gone before anyone notices.

Notable interactions covered in the wiki

• linux-7-postgres-regression — Linux 7.0 removed PREEMPT_NONE (see linux-preemption-models), letting the scheduler preempt a backend mid–page fault while it holds the StrategyGetBuffer spinlock. On a 96-vCPU Graviton4 with 120 GB shared_buffers and 4 KB pages, every other backend spins on a held lock; throughput halves. Workaround: enable huge-pages.
• linux-kernel-pgit — pgit ingests Linux kernel git history into PostgreSQL so it's queryable as SQL. Different angle on the same database.

Repo

https://github.com/postgres/postgres