Online alter behavior

[Christopher Powers]

Hi guys,

My understanding of the online alter API is as follows:

1. check_if_supported_alter()
    - Confirm that handler can perform operation online

2. alter_table_phase1()
    - Notify handler to prepare for alter

3. alter_table_phase2()
    - Command handler to execute alter

4. alter_table_phase3()
    - Notify handler that changes are persisted, table is re-opened

If the handler returns an error in steps 2 or 3 then the server triggers 
an assertion. Is this the intended behavior?

Thanks,

Chris