Default Isolation Levels

The default isolation level is established when you create the database.
HCL OneDB™ Name ANSI Name When This Is the Default Level of Isolation
Dirty Read Read Uncommitted Database without transaction logging
Committed Read Read Committed Databases with logging that are not ANSI- compliant
Repeatable Read Serializable ANSI-compliant databases

For HCL OneDB databases that are not ANSI-compliant, unless you explicitly set the USELASTCOMMITTED configuration parameter, the LAST COMMITTED feature is not in effect for the default isolation levels. The SET ENVIRONMENT statement or the SET ISOLATION statement can override this default and enable LAST COMMITTED for the current session.

The default isolation level remains in effect until you issue a SET TRANSACTION statement within a transaction. After a COMMIT WORK statement completes the transaction or a ROLLBACK WORK statement cancels the entire transaction, the isolation level is reset to the default.

When you use High Availability Data Replication, the database server effectively uses Dirty Read isolation on the HDR Secondary Server, regardless of the specified SET ISOLATION or SET TRANSACTION isolation level, unless the UPDATABLE_SECONDARY configuration parameter is enabled. For more information about this topic, see Isolation Levels for Secondary Data Replication Servers.