Slave process?

Question

Hi all,
what is slave process?
why we use slave process?
when it is used?
just i need outlined. concept.
Thanks in advance,
regards,
DB

Answer 1

TSharma wrote:
Slave Processe_s
Slave processes are background processes that perform work on behalf of other processes. This section describes some slave processes used by Oracle Database.
I/O Slave Processes_
I/O slave processes (Innn) simulate asynchronous I/O for systems and devices that do not support it. In asynchronous I/O, there is no timing requirement for transmission, enabling other processes to start before the transmission has finished.
For example, assume that an application writes 1000 blocks to a disk on an operating system that does not support asynchronous I/O. Each write occurs sequentially and waits for a confirmation that the write was successful. With asynchronous disk, the application can write the blocks in bulk and perform other work while waiting for a response from the operating system that all blocks were written.
To simulate asynchronous I/O, one process oversees several slave processes. The invoker process assigns work to each of the slave processes, who wait for each write to complete and report back to the invoker when done. In true asynchronous I/O the operating system waits for the I/O to complete and reports back to the process, while in simulated asynchronous I/O the slaves wait and report back to the invoker.
The database supports different types of I/O slaves, including the following:
I/O slaves for Recovery Manager (RMAN)
When using RMAN to back up or restore data, you can make use of I/O slaves for both disk and tape devices.
Database writer slaves
If it is not practical to use multiple database writer processes, such as when the computer has one CPU, then the database can distribute I/O over multiple slave processes. DBWR is the only process that scans the buffer cache LRU list for blocks to be written to disk. However, I/O slaves perform the I/O for these blocks.
Parallel Query Slaves_
In parallel execution or parallel processing, multiple processes work together simultaneously to run a single SQL statement. By dividing the work among multiple processes, Oracle Database can run the statement more quickly. For example, four processes handle four different quarters in a year instead of one process handling all four quarters by itself.
Parallel execution reduces response time for data-intensive operations on large databases such as data warehouses. Symmetric multiprocessing (SMP) and clustered system gain the largest performance benefits from parallel execution because statement processing can be split up among multiple CPUs. Parallel execution can also benefit certain types of OLTP and hybrid systems.
In Oracle RAC systems, parallel execution is controlled by the service placement of a particular service. Specifically, parallel processes run on the nodes on which you have configured the service. By default, Oracle Database runs the parallel process only on the instance that offers the service used to connect to the database. This does not affect other parallel operations such as parallel recovery or the processing of GV$ queries.You could simply share the source url,
http://docs.oracle.com/cd/E11882_01/server.112/e25789/process.htm#BABDJBDI
Aman....