docs: document MariaDB backends in the README

Merged
RE
2mo ago
+31-3

Prep for the v2.5.0 release. The MariaDB GTID support merged in #49 is the
reader's headline feature, but the README did not mention MariaDB at all — so
the release notes would point readers at a page that still describes a
MySQL-only tool.

Documents what an operator needs to know:

  • No flag is required; the backend is detected from the version banner.
  • The snapshot comes from @@gtid_binlog_pos, since MariaDB has no
    Executed_Gtid_Set column.
  • An empty @@gtid_binlog_pos is a valid empty position, not a startup failure.
  • Domain ids are canonical decimal uint32, so 0 and 00 never name the
    same domain.

The one thing most likely to be got wrong is called out explicitly: the native
MariaDB spelling domain-server-sequence is not the wire format. The
reader sends GTID_Set::to_string(), i.e. domain:start-end. Someone
comparing @@gtid_binlog_pos against the reader's output would otherwise
conclude the reader was broken.

Also corrects two MySQL-only claims (the HowTo preamble, and the
integration-test description, which omitted the MariaDB 10.11 service the TAP
suite uses).

Docs only — no code change. The new section was written against the merged
implementation in #49 and cross-checked against the reader's own --help
output and the test assertions.

Blocks cutting v2.5.0: the release notes reference the README as the option
and configuration reference, so it should describe the released behaviour.

Summary by cubic

Prepares the v2.5.0 release by documenting MariaDB backend support in the README, which the MariaDB GTID feature merged in the release had never mentioned. Docs only — no code change.

  • No flag is required; the backend is detected from the version banner and the snapshot is read from @@gtid_binlog_pos, not the MySQL Executed_Gtid_Set column.
  • An empty @@gtid_binlog_pos is a valid empty position, not a startup failure.
  • The native MariaDB spelling domain-server-sequence is not the wire format; the reader sends domain:start-end via GTID_Set::to_string(), so a position from @@gtid_binlog_pos will not match the reader's output.
  • Domain ids are canonical decimal uint32; non-canonical spellings are rejected, so 0 and 00 are not the same domain.
  • Corrects two MySQL-only claims: the HowTo preamble and the integration-test description, which omitted the MariaDB 10.11 TAP service.

Summary by CodeRabbit

  • Documentation
    • Added instructions for using MariaDB as a backend, including GTID snapshot and stream testing.
    • Clarified MariaDB GTID formats, domain ID requirements, and handling of an empty starting GTID position.