Transaction isolation limitations with in-memory tables
When you use in-memory tables (M-tables), be aware of the following limitations that are associated with transaction isolation.
The SERIALIZABLE isolation level is not supported with M-tables
You cannot use M-tables in transactions where the transaction isolation level is SERIALIZABLE. The only levels of transaction isolation that are supported for M-tables are REPEATABLE READ and READ COMMITTED. For more information about transaction isolation levels, see Controlling transaction isolation levels.
For M-tables in the HotStandby secondary server, the transaction isolation level is always READ COMMITTED
If you are using HotStandby (HSB) and you connected to the HSB secondary server then, when you read data from in-memory tables, the transaction isolation level is automatically set to READ COMMITTED, even if you specified REPEATABLE READ.
REPEATABLE READ related differences between M-tables and D-tables
If you use M-tables and set the transaction isolation level to REPEATABLE READ (the default is READ COMMITTED), read operations block write operations for the duration of the read transaction. Moreover, with the REPEATABLE READ isolation level, deadlocks are possible with M-tables whereas they cannot occur on versioning disk-based tables (D-tables). Also, concurrency conflicts can occur when optimistic concurrency control is in use.