Looking at Rdb_binlog_manager in FB/MySQL.
It stores the master position in this record:
Uses for that information:
- It is printed to stderr on server startup (see rocksdb_recover()).
- It is used to move the binlog position forward during recovery:
(This targets the usecase with sync_binlog !=1 and innodb_flush_log_at_trx_commit !=1)
- It is visible through INFORMATION_SCHEMA.ROCKSDB_GLOBAL_INFO.
Re #2, InnoDB in FB/MySQL has similar code in is_binlog_advanced (and MariaDB's InnoDB doesn't have it)
When slave-gtid-info=optimized option is used, mysql.slave_gtid_info is kept up-todate directly by the storage engines. (See https://github.com/facebook/mysql-5.6/commit/0f402cb8381ba9d8e71c93085a22e5a12589b6e3)
(Q: and that option is not used, both the SE and the SQL layer do the updates?)
- Neither of the above features are essential (or storage engine-only)
- MariaDB has an error when trying to use a part of Rdb_binlog_manager (as it doesn't have binlog position stored). We need to disable it.