This module contains utilities for working with PostgreSQL file formats. It's a collection of structs that are auto-generated from the PostgreSQL header files using bindgen, and Rust functions to read and manipulate them.
There are also a bunch of constants in pg_constants.rs that are copied
from various PostgreSQL headers, rather than auto-generated. They mostly
should be auto-generated too, but that's a TODO.
The PostgreSQL on-disk file format is not portable across different
CPU architectures and operating systems. It is also subject to change
in each major PostgreSQL version. Currently, this module supports
PostgreSQL v14 and v15: bindings and code that depends on them are version-specific.
This code is organized in modules: postgres_ffi::v14 and postgres_ffi::v15
Version independend code is explicitly exported into shared postgres_ffi.
TODO: Currently, there is also some code that deals with WAL records in pageserver/src/waldecoder.rs. That should be moved into this module. The rest of the codebase should not have intimate knowledge of PostgreSQL file formats or WAL layout, that knowledge should be encapsulated in this module.