9ede38b6c4
A new `get_lsn_by_timestamp` command is added to the libpq page service API. An extra timestamp field is now stored in an extra field after each Clog page. It is the timestamp of the latest commit, among all the transactions on the Clog page. To find the overall latest commit, we need to scan all Clog pages, but this isn't a very frequent operation so that's not too bad. To find the LSN that corresponds to a timestamp, we perform a binary search. The binary search starts with min = last LSN when GC ran, and max = latest LSN on the timeline. On each iteration of the search we check if there are any commits with a higher-than-requested timestamp at that LSN. Implements github issue 1361.
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.