We have been testing Galera-MariaDB on data consistency models. We (together with the Galera contributor) found REPEATABLE READ anomalies with Galera disabled. Hence, there might be something wrong with MariaDB. We used the default REPEATABLE READ isolation in our testing.
The collected data (or histories of transaction executions):
The specific anomaly was shown at https://github.com/codership/galera/issues/609#issuecomment-1036096287 Also see the table attached.
Notation: w/r(key, value, client_id, txn_id); operations of a txn (denoted by a column) are listed from top down.
Anomaly: txn393 read value 3328 on key 0 (red cell, column 1) in between the reads of value 33324 on key 0 (yellow cells).
Setup: 3 server nodes and 3 client nodes. Galera Version: 26.4.9. MariaDB Version: 10.4.22.