Oracle Tips  by Burleson Consulting

The Data Warehouse Development Life Cycle

Parallelism And Oracle Data Warehousing

Parallel Create Table As Select

Parallel Create Table As Select (PCTAS) can be very useful in an Oracle data warehouse environment where tables are replicated across numerous servers or when pre-aggregating roll-up summary tables. Parallel Create Table As Select is also very useful when performing roll-up activities against your Oracle warehouse. For example, we could specify the number of parallel processes to compute the monthly summary values from our fact table. In the following example, we assign five processes to simultaneously read the blocks from the customer table.

CREATE TABLE REGION_SALESPERSON_SUMMARY_03_97
PARALLEL (degree 5)
AS
SELECT region, salesperson, sum(sale_amount)
FROM FACT
SEE CODE DEPOT FOR FULL SCRIPT

Here, we dedicate five query servers to extract the data from the fact table and five query servers to populate the new summary table (see Figure 7.9).

Figure 7.9 Parallel Create Table As Select.

Again, we must remember that it is not necessary to have SMP or MPP hardware to benefit from parallel query techniques. Even a single-processor Unix system will experience some improvement from using parallel processes, even though all of the processes are running on the same CPU.

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