Processes Of Oracle
Oracle Processes
A database is started on a database Server, a memory area is called the System Global Area (SGA). SGA is allocated and one or more Oracle process starts. The combination of SGA and the Oracle Processes is called an Oracle database Instance.
- Database writer (DBWR)
- Log Writer (LGWR)
- Checkpoint (CKPT)
- System Monitor (SMON)
- Process Monitor (PMON)
- Archive (ARCH)
- Recover (RECO)
- LOCK (LCKn)
- Dispatcher (Dnnn)
- Server (Snnn)
Database Writer (DBWR)
All the writing of buffers of the data files is performed by the database writer process (DBWR). It is responsible for buffer cache management. When a buffer in the buffer cache is modified, it is marked “Dirty”, the primary job of the DBWR process is to keep the buffer cache “clean” by writing “Dirty” buffers to the disk. LRU (Least recently used) algorithm keeps the most recently used data blocks in the memory, thereby minimize disk I/O.
Log Writer (LGWR)
The Log Writer is written to a REDO log on the disk by the Log Writer process.
Check point (CKPT)
DBWR is required to write all the blocks, which have been modified. Before the last check point to the data files and update, the data files header and control files records the check point.
System Monitor (SMON)
Instance recovery is at instance start up. SMON is also responsible to clean the temporary files , which are no longer in use.
Process Monitor (PMON)
Process Monitor is used to process the recovery, when a user process fails.
Recover (RECO)
This process is used with the Distributed Option that automatically resolves the failure involving the distributing transactions.
Archive (ARCH)
Archive is present, only when the redo log is used in ARCHIVELOG mode and archive log mode is automatic enabled.
Lock (LCKn)
Up to ten lock process (LCK0, …, LCK9) are used for the instance locking.
Dispatcher Process (Dnnn)
This process allows the user processes to share a limited number of the Server processes.
Summary
Thus, we learned that a database is started on a database Server. A memory area is called the System Global Area (SGA). SGA is allocated and one or more Oracle processes starts. The combination of SGA and the Oracle processes is called an Oracle database instance.