Performance depends on the Oracle version you use. Locks are generated anyway.
If version <= Oracle 11.1 then #1 does the same as #2. It is slow anyway.
Beginning with Oracle 11.2, Oracle introduced a great optimization for the first statement (one command doing it all). You don’t need to change the command – Oracle just behaves differently. It stores the default value only in data dictionary instead of updating each physical row.
But I also have to say, that I encountered some bugs in the past related to this feature (in Oracle 11.2.0.1)
- failure of traditional import if export was done with direct=Y
- merge statement can throw an ORA-600 [13013] (internal oracle error)
- a performance problem in queries using such tables
I think this issues are fixed in current version 11.2.0.3, so I can recommend to use this feature.