Oracle began providing its own volume manager software for Linux and Windows in
Oracle9i Release 2. Since Oracle Database 10g, database releases for all supported
operating systems include a cluster file system and volume manager in the database
that is leveraged by ASM. When using ASM, it is recommended that you not try to
leverage an operating system volume manager.
Consider an Oracle database with an 8 KB data block size and the DB_FILE_
MULTIBLOCK_READ_COUNT initialization parameter set to 32. There will be two
sizes of I/O by Oracle: a single 8 KB data block and a 256 KB multiblock read (32 times
8 KB).
Two types of parallelism are possible within an Oracle database:
Block-range parallelism Driven by ranges of database blocks
ability to dynamically parallelize table scans and a variety of scan-based functions.Oracle7 implemented blockrange parallelism by dynamically breaking a table into pieces, each of which was a range of blocks, and then used multiple processes to work on these pieces in parallel.
Partition-based parallelism Driven by the number of partitions or subpartitions involved in the operation.
With partitioned tables, introduced in Oracle8, an operation may involve one, some, or all of the partitions of a partitioned table.
An Oracle instance has a pool of parallel execution (PE) processes that are available to the database users. Oracle8i introduced the notion of self-tuning adaptive parallelism. This feature automatically scales down parallelism as the system load increases and scales it back up as the load decreases.(193)