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1.
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What constitute an ORACLE Instance? |
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SGA and ORACLE background processes constitute an ORACLE
instance. (or) Combination of memory structure and
background process.
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2.
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What is SGA? |
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The System Global Area (SGA) is a shared memory region
allocated by ORACLE that contains data and control
information for one ORACLE instance.
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3.
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What are the components of SGA? |
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Database buffers; Redo Log Buffer the Shared Pool and
Cursors.
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4.
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What do Database Buffers contain? |
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Database buffers store the most recently used blocks of
database data. It can also contain modified data that
has not yet been permanently written to disk.
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5.
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What do Redo Log Buffers contain? |
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Redo Log Buffer stores redo entries a log of changes
made to the database.
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6.
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What is Shared Pool? |
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Shared Pool is a portion of the SGA that contains shared
memory constructs such as shared SQL areas.
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7.
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What is Shared SQL Area? |
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A Shared SQL area is required to process every unique
SQL statement submitted to a database and contains
information such as the parse tree and execution plan
for the corresponding statement.
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8.
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What is Cursor? |
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A Cursor is a handle (a name or pointer) for the memory
associated with a specific statement.
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9.
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What is PGA? |
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Program Global Area (PGA) is a memory buffer that
contains data and control information for a server
process.
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10. |
What is User Process? |
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A user process is created and maintained to execute the
software code of an application program. It is a shadow
process created automatically to facilitate
communication between the user and the server process.
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11. |
What is Server Process? |
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Server Process handles requests from connected user
process. A server process is in charge of communicating
with the user process and interacting with ORACLE carry
out requests of the associated user process.
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12. |
What are the two types of Server Configurations? |
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Dedicated Server Configuration and Multi-threaded Server
Configuration.
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13. |
What is Dedicated Server Configuration? |
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In a Dedicated Server Configuration a Server Process
handles requests for a Single User Process.
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14. |
What is a Multi-threaded Server Configuration? |
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In a Multi-threaded Server Configuration many user
processes share a group of server process.
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15. |
What is a Parallel Server option in ORACLE? |
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A configuration for loosely coupled systems where
multiple instances share a single physical database is
called Parallel Server.
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16. |
Name the ORACLE Background Process? |
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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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17. |
What Does DBWR do? |
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Database writer writes modified blocks from the database
buffer cache to the data files.
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18. |
When Does DBWR write to the database? |
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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.
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19. |
What does LGWR do? |
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Log Writer (LGWR) writes redo log entries generated in
the redo log buffer of the SGA to on-line Redo Log File.
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20. |
When does LGWR write to the database? |
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LGWR writes redo log entries into an on-line redo log
file when transactions commit and the log buffer files
are full.
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21. |
What is the function of checkpoint (CKPT)? |
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The Checkpoint (CKPT) process is responsible for
signaling DBWR at checkpoints and updating all the data
files and control files of the database.
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22. |
What are the functions of SMON? |
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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.
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23. |
What are functions of PMON? |
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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.
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24. |
What is the function of ARCH? |
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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.
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25. |
What is function of RECO? |
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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.
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26. |
What is the function of Dispatcher (Dnnn)? |
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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.
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27. |
How many Dispatcher Processes are created? |
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Atleast one Dispatcher process is created for every
communication protocol in use.
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30. |
What is the function of Lock (LCKn) Process? |
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Lock (LCKn) is used for inter-instance locking when the
ORACLE Parallel Server option is used.
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31. |
What is the maximum number of Lock Processes used? |
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Though a single LCK process is sufficient for most
Parallel Server systems upto Ten Locks (LCK0,....LCK9)
are used for inter-instance locking.
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