The new debug_io_direct flag only triggers direct IO in very limited cases, and is only tangentially related to the AIO patchset discussed in that thread. Note

The new debug_io_direct flag only triggers direct IO in very limited cases, and is only tangentially related to the AIO patchset discussed in that thread. Note that the documentation on the config flag explicitly warns about not using it in production: > Currently this feature reduces performance, and is intended for developer testing only. Also note that very few things will actually do IO during commit - the only IO that I can think of are 1.) the WAL-logging of the commit (often small, a few 100 bytes at most), and 2.) replying to the COMMIT command (10s of bytes at most). It is quite unlikely that this will see much performance benefit from IO_DIRECT without further infrastructure inside PostgreSQL around io_uring and other async kernel IO apis.