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feae7f39c1
Change 'zenith.signal' file to a human-readable format, similar to
backup_label. It can contain a "PREV LSN: %X/%X" line, or a special
value to indicate that it's OK to start with invalid LSN ('none'), or
that it's a read-only node and generating WAL is forbidden
('invalid').
The 'zenith pg create' and 'zenith pg start' commands now take a node
name parameter, separate from the branch name. If the node name is not
given, it defaults to the branch name, so this doesn't break existing
scripts.
If you pass "foo@<lsn>" as the branch name, a read-only node anchored
at that LSN is created. The anchoring is performed by setting the
'recovery_target_lsn' option in the postgresql.conf file, and putting
the server into standby mode with 'standby.signal'.
We no longer store the synthetic checkpoint record in the WAL segment.
The postgres startup code has been changed to use the copy of the
checkpoint record in the pg_control file, when starting in zenith
mode.
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.