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This type
of parallelism improves the performance of large bulk operations (for example, an
update to all the rows of a very large table).
In Oracle8 the degree of parallelism for updates and deletes is tied to the number of
partitions involved, while in Oracle8i and beyond the degree of parallelism for
updates and deletes is tied to the number of partitions or subpartitions involved. A
table with 12 partitions (for example, one partition for each month of the year) can
have a maximum number of 12 PEs for an update or delete. An update to only one
month of data would have no parallelism because it involves only one partition. If
the table were created using Oracle??™s composite partitioning (for example, with 4
hash subpartitions by PRODUCT_ID within each month), the maximum degree of
parallelism for the entire table would be 48, or 12 partitions with 4 subpartitions
each. An update to one month of data could have a degree of 4 because each month
contains 4 hash subpartitions. If the table is not partitioned, Oracle cannot perform
updates or deletes in parallel.


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