Introduction to Background processesWhen you start a routine, Oracle allocates not only the SGA, but also the background process, and when the routine is closed, Oracle frees up the memory space that the SGA consumes, and it frees the CPU and memory resources that the background process consumes. Oracle provides a number of background processes, which describe common background processes Smon, Pmon, DBWR, LGWR, CKPT, and ARCH. Category Introduction1. DBWR Database Write ProcessDBWR The database writer process is responsible for writing the dirty blocks from the data cache (database block buffer) back to the disk. When a transaction modifies data in a block, it does not need to write the block back to disk immediately. Due to the advanced mechanism used by Oracle, the modified data can not be immediately written back, and timely failure will not be lost. Therefore, DBWR can take a more efficient writeback method without having to write back immediately after the transaction has been committed. DBWR typically write back data periodically, unless the data buffer needs to be emptied or full. the least Recently used principle (least-recently-used) is used for data writeback. For systems that support asynchronous I/O, only one BWR process can be used, which increases the efficiency by increasing the number of DBWR that do not support asynchronous IO. 2. LGWR Log Write ProcessLgwr (the log writer process) is responsible for writing the data in the log buffer to the redo log. System performance is susceptible to LGWR because the commit operation relies on the LGWR writeback log (commit action triggers LGWR to write the log buffer data to the undo log). 3. Pmon Process Monitoring ProcessPmon is responsible for monitoring the processing of the database and for cleaning up the dead process. Pmon also responsible for restarting the failed scheduling process (dispatcher process)4. Smon System Monitoring Processthe Smon (the system Monitor process) session is responsible for recovering instances when the instance is started, including clearing temporary segments and recovering things that were interrupted by a system crash. Smon can also purge fragments in the database by merging free partitions5.CKPT Checkpoint ProcessThe CKPT process is responsible for sending signals to the DBWR process, requiring a checkpoint and updating all data and control files for the database. CheckPoint (checkpoint) refers to a DBWR process that writes all the modified data buffers back to the data file. Ckpt is optional, and if there is no ckpt process, these tasks are LGWR. 6. Archn Archive ProcessARCH (The archiver Process) is responsible for copying the replay redo log to the archive memory. Arch is effective when the input RDBMS is running in Archivelog mode, and if the system is not running in Archivelog mode, the system may fail to recover after it fails. Finally, let the system run in Archivelog mode, at which time there may be more than one archive process. sql>archive Log list//To see if it is in archive modeArchive can be opened in the database mount modesql>alter database Archivelog;//Opensql>alter database noarchivelog;//off7. RECO Recovery ProcessRECO (the Recovery process) processes are used to purge pending (pending) transactions in the distributed database, which is responsible for the commit and rollback of the local part of the distributed transaction8. DNNN Scheduling ProcessIf the multithreaded server option is selected, there is at least one scheduling process for each communication protocol used. The dispatch process (the Dispatcher process,dnnn) forwards the request of the user process to an available shared server process and is responsible for forwarding the request of the user process to an available shared server process and is responsible for echoing the response message. 9. snnn Shared Server processwhen using a shared server configuration or MTS, a shared server process (the GKFX Servers process, snnn) is used. These processes are like dedicated server processes (dedicated server process), but can be made available to multiple users shared. LMS Oracle RAC Lock Management Servicewhen using RAC, the service term manages locks between different nodes in the cluster.qmnn Queue Management processwith the Advanced queue option (queueing option), the Queue Manager process is used to manage the job queue, with a queue number of up to 10, Qmn0--qmn9
Oracle Background process
