e., the number of parallel execution
processes used for the table as a whole) is applied to the set of partitions that
will be used for an operation. The optimizer will eliminate the use of partitions that
do not contain data an operation will use. For instance, if one of the partitions for a
table contains ID numbers below 1,000, and if a query requests ID numbers between
1,100 and 5,000, the optimizer understands that this query will not access this
partition.
Since Oracle9i, youcan also partition tables based on a list of specific values,
although this type of partitioning is typically used to partition tables for maintenance
operations. As explained in Chapter 4, Oracle has continued to add more
choices in ways to implement partitioning.
If you expect that your queries will use partition elimination or pruning and you plan
on using parallelism, you should stripe each partition over a sufficient number of
drives to scale effectively. This will ensure scalability regardless of the number of partitions
accessed. This striping can be achieved manually through the use of multiple
datafiles on multiple disks, through the use of striped arrays, or through a combination
of both approaches.
Pages:
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385