The rules for creating and altering indexes are discussed in the following topics:
The CREATE INDEX and ALTER INDEX REBUILD statements can be parallelized only by a PARALLEL clause or an ALTER SESSION FORCE PARALLEL DDL statement.
The ALTER INDEX REBUILD statement can be parallelized only for a nonpartitioned index, but ALTER INDEX REBUILD PARTITION can be parallelized by a PARALLEL clause or an ALTER SESSION FORCE PARALLEL DDL statement.
The scan operation for ALTER INDEX REBUILD (nonpartitioned), ALTER INDEX REBUILD PARTITION, and CREATE INDEX has the same parallelism as the REBUILD or CREATE operation and uses the same DOP. If the DOP is not specified for REBUILD or CREATE, the default is the number of CPUs.
The ALTER INDEX MOVE PARTITION and ALTER INDEX SPLIT PARTITION statements can be parallelized only by a PARALLEL clause or an ALTER SESSION FORCE PARALLEL DDL statement. Their scan operations have the same parallelism as the corresponding MOVE or SPLIT operations. If the DOP is not specified, the default is the number of CPUs.