All Your GUCs in a Row: io_method and io_workers

A detailed breakdown of PostgreSQL 18's io_method and io_workers GUCs, which control the asynchronous I/O execution engine introduced with the new AIO subsystem. io_method (postmaster context, requires restart) selects between sync, worker (the default, portable across platforms), and io_uring (fastest but requires --with-liburing, a current Linux kernel, and permissive seccomp policies). io_workers sizes the worker pool for worker mode; the piece corrects an earlier claim that this required a restart—it's actually sighup context and can be changed with just a reload. The default pool size of 3 is tuned for minimal hardware, and an undersized pool silently degrades to synchronous I/O rather than erroring, visible via the AioWorkerSubmissionQueue LWLock wait event in pg_stat_activity. Recommendations: use io_uring where your kernel and security policy allow it, otherwise stay on worker, and size io_workers based on observed queue contention rather than guesswork, since PostgreSQL 19 will self-size the pool.

Source: https://postgr.es/p/9se. 8 Sync News only summarizes and links out; content copyright belongs to the authors and original sources.