This is a new feature in Dynamics AX 4.0 to set global concurreny model for database changes. The settings can siginificanly affect database performance.
Optimistic concurrency mode enabled per table
This setting, which is the default, enables individual tables to be configured to work under a specific concurrency mode. When this option is selected, the concurrency mode is initially set to optimistic concurrency for all tables, with a few exceptions. The table property OccEnabled can be changed for any table as appropriate.
Optimistic concurrency mode enabled globally
Enables optimistic concurrency mode for all tables.
Pessimistic concurrency mode enabled globally
Enables pessimistic concurrency mode for all tables.
Use the READ UNCOMMITTED transaction isolation level for all Microsoft SQL Server 2000 database reads - Can be used to reduce blocking for installations running on Microsoft SQL Server 2000 databases.
Log all UPDATE conflict exceptions
Writes all UPDATE conflict exceptions to the log. It's recommended to select this setting.