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Update 'postgres_ffi' module's readme file and comments.

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Explain the purpose of of the 'postgres_ffi' module, explain what the
PostgreSQL control file is, and some other minor cleanup.
This commit is contained in:
Heikki Linnakangas
2021-06-04 23:05:11 +03:00
parent 762e9859d6
commit d18cc8a3a8
5 changed files with 77 additions and 5 deletions
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25
postgres_ffi/src/controlfile_utils.rs
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@@ -1,3 +1,28 @@
//!
//! Utilities for reading and writing the PostgreSQL control file.
//!
//! The PostgreSQL control file is one the first things that the PostgreSQL
//! server reads when it starts up. It indicates whether the server was shut
//! down cleanly, or if it crashed or was restored from online backup so that
//! WAL recovery needs to be performed. It also contains a copy of the latest
//! checkpoint record and its location in the WAL.
//!
//! The control file also contains fields for detecting whether the
//! data directory is compatible with a postgres binary. That includes
//! a version number, configuration options that can be set at
//! compilation time like the block size, and the platform's alignment
//! and endianess information. (The PostgreSQL on-disk file format is
//! not portable across platforms.)
//!
//! The control file is stored in the PostgreSQL data directory, as
//! `global/pg_control`. The data stored in it is designed to be smaller than
//! 512 bytes, on the assumption that it can be updated atomically. The actual
//! file is larger, 8192 bytes, but the rest of it is just filled with zeros.
//!
//! See src/include/catalog/pg_control.h in the PostgreSQL sources for more
//! information. You can use PostgreSQL's pg_controldata utility to view its
//! contents.
//!
use crate::{ControlFileData, PG_CONTROLFILEDATA_OFFSETOF_CRC, PG_CONTROL_FILE_SIZE};
use bytes::{Buf, Bytes, BytesMut};

5
postgres_ffi/src/pg_constants.rs
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@@ -1,6 +1,11 @@
//!
//! Misc constants, copied from PostgreSQL headers.
//!
//! TODO: These probably should be auto-generated using bindgen,
//! rather than copied by hand. Although on the other hand, it's nice
//! to have them all here in one place, and have the ability to add
//! comments on them.
//!
//
// From pg_tablespace_d.h