1. What Does DBWR do?
Database writer writes modified blocks from the database buffer cache to the data files.
2. When Does DBWR write to the database?
DBWR writes when more data needs to be read into the SGA and too few database buffers are free. The least recently used data is written to the data files first. DBWR also writes when CheckPoint occurs.
3. What does LGWR do?
Log Writer (LGWR) writes redo log entries generated in the redo log buffer of the SGA to on-line Redo Log File.
4. When does LGWR write to the database?
LGWR writes redo log entries into an on-line redo log file when transactions commit and the log buffer files are full.
5. What is the function of checkpoint (CKPT)?
The Checkpoint (CKPT) process is responsible for signaling DBWR at checkpoints and updating all the data files and control files of the database.
6. What are the functions of SMON?
System Monitor (SMON) performs instance recovery at instance start-up. In a multiple instance system (one that uses the Parallel Server), SMON of one instance can also perform instance recovery for other instance that have failed SMON also cleans up temporary segments that are no longer in use and recovers dead transactions skipped during crash and instance recovery because of file-read or off-line errors. These transactions are eventually recovered by SMON when the tablespace or file is brought back on-line SMON also coalesces free extents within the database to make free space contiguous and easier to allocate.
7. What are functions of PMON?
Process Monitor (PMON) performs process recovery when a user process fails PMON is responsible for cleaning up the cache and Freeing resources that the process was using PMON also checks on dispatcher and server processes and restarts them if they have failed.
8. What is the function of ARCH?
Archiver (ARCH) copies the on-line redo log files to archival storage when they are full. ARCH is active only when a database's redo log is used in ARCHIVELOG mode.
9. What is function of RECO?
RECOver (RECO) is used to resolve distributed transactions that are pending due to a network or system failure in a distributed database. At timed intervals, the local RECO attempts to connect to remote databases and automatically complete the commit or rollback of the local portion of any pending distributed transactions.
10. What is the function of Dispatcher (Dnnn)?
Dispatcher (Dnnn) process is responsible for routing requests from connected user processes to available shared server processes and returning the responses back to the appropriate user processes.
11. How many Dispatcher Processes are created?
At least one Dispatcher process is created for every communication protocol in use.
12. What is the function of Lock (LCKn) Process?
Lock (LCKn) are used for inter-instance locking when the ORACLE Parallel Server option is used.
13. What is the maximum number of Lock Processes used?
Though a single LCK process is sufficient for most Parallel Server systems
Upto Ten Locks (LCK0,....LCK9) are used for inter-instance locking.
14. Name the ORACLE Background Process ?
DBWR - Database Writer.
LGWR - Log Writer
CKPT - Check Point
SMON - System Monitor
PMON - Process Monitor
ARCH - Archiver
RECO - Recover
Dnnn - Dispatcher, and
LCKn - Lock
Snnn - Server.
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