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c77e30116e
Move the code for decoding a WAL stream into WAL records into 'postgres_ffi', and keep the code to parse the WAL records deeper in 'pageserver' crate, renamed to walrecord.rs. This tidies up the dependencies a bit. 'walkeeper' reuses the same waldecoder routines, and it used to depend on 'pageserver' because of that. Now it only depends on 'postgres_ffi'. (The comment in walkeeper/Cargo.toml that claimed that the dependency was needed for ZTimelineId was obsolete. ZTimelineId is defined in 'zenith_utils', the dependency was actually needed for the waldecoder.)
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 is based on PostgreSQL v14, but in the future we will probably need a separate copy for each PostgreSQL version. 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.