Oracle I/O subordinate Process

Oracle I/O slave process www.2cto.com I/O slave process is used to simulate asynchronous I/O for systems or devices that do not support asynchronous I/O. for example, tape devices (relatively slow) do not support asynchronous I/O. by using an I/O slave process, you can enable the tape drive to mimic the features normally provided only for the disk drive. Just like supporting real asynchronous I/O, device-writing processes (callers) collect a large amount of data and write the data to the writer. When data is successfully written, the writer notifies the original caller that the writer is an I/O-dependent process, not an operating system, the caller deletes the data from the data list to be written. In this way, we can get a higher throughput, because the I/O sub-process will wait for the slow device, and the original call process will be able to get away from it, you can do other important work to collect the data to be written next time. The I/O slave process has two purposes in Oracle. DBWn and LGWR can use the I/O slave process to simulate asynchronous I/O, and RMAN may also use the I/O slave process when writing the tape. Two parameters control the use of the I/O slave process: www.2cto.com BACKUP_TAPE_IO_SLAVES: this parameter specifies whether RMAN uses the I/O slave process to back up, copy, or restore data to tape. This parameter is a Boolean value because it is designed for tape devices and can only be accessed by one process at a time, instead of using the number of subordinate processes (which may be unexpected ). RMAN starts multiple necessary processes for the physical device in use. When BACKUP_TAPE_IO_SLAVES = TRUE, an I/O slave process is used to read and write data from the tape device. If this parameter is set to FALSE (default), the backup will not be performed using the I/O slave process. Instead, the dedicated server process that completes the backup directly accesses the tape device. DBWR_IO_SLAVES: this parameter specifies the number of I/O subordinate processes used by the DBW0 process. The DBW0 process and its subordinate processes always write dirty blocks in the buffer cache to the disk. The default value is 0, indicating that I/O subordinate processes are not used. Note: If you set this parameter to a non-0 value, LGWR and ARCH will also use their own I/O subordinate processes, LGWR and ARCH allow up to four I/O subordinate processes. The name of the dbwr I/O subordinate process is I1nn, and the name of the LGWRI/O subordinate process is I2nn, where nn is a number. The Subprocess www.2cto.com Oracle7.1.6 introduces the parallel query function. This function is used to CREATE an execution plan for SQL statements such as SELECT, CREATE TABLE, CREATE INDEX, and UPDATE, including multiple (sub) Execution plans that can be completed at the same time. Merge the output of each execution plan to form a larger result. The goal is to complete the operation in a small amount of time, which is only a small part of the time required to complete the same operation in a serial mode. For example, assume that a large table is distributed on 10 different files. You have 16 CPUs configured and need to execute an ad hoc query on this table. Another way is to break down the query plan into 32 smaller parts and take full advantage of the machine, instead of using only one process to read and process all data serially. In contrast, the previous approach is much better. When you use parallel query, you will see processes named Pnnn, which are subordinate processes of parallel query. When processing a parallel statement, the server process is called the parallel query coordinator ). The name of the server process on the operating system does not change. However, if you refer to the Coordinator process when reading the documents about parallel queries, you should know that this is the original server process.