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Oracle System Architecture Interview Questions

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What is pga ?

Asked By: Interview Candidate | Asked On: Sep 6th, 2004

Program GLobal area (pga) is a memory buffer that contains data and control information for a server process.

Answered by: NARESH KUMAR on: Sep 18th, 2012

Pga is a memory area that contains data and control information for the oracle server processes. The size and contains of the pga depends on the Oracle server options we have installed.

Answered by: NAGARAJ OCP on: Dec 27th, 2011

Main function of PGA is SORTING(Order by, Join and so on) will takes place on PGA memory.. If PGA memory is not enough in such cases temporary tablespaces will be used.

Database security

Asked By: hashmi1 | Asked On: Dec 11th, 2010

What is database security? How will you use it?

Answered by: sri on: Feb 20th, 2012

That is Acl . Those levels are

Manager,
designer,
editor,
author,
reader,
depositor,
no access

What is sga? Where it is located? Why the system performance will be slow after loading the Oracle?

Asked By: madhu | Asked On: Sep 5th, 2006

Answered by: NAGARAJ OCP on: Dec 27th, 2011

Dont install oracle on C:(or on which drive you installed OS). Its not sure that it gives you great result, it better result then previous one.

Answered by: manish hoiyani on: Sep 18th, 2006

sga stands fro system global area.. which is the part of the oracle instance(includes memory struture and background processes). for faster executon and better performance everthing comes in the sga.s...

What do database buffers contain ?

Asked By: Interview Candidate | Asked On: Sep 6th, 2004

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.

Answered by: NAGARAJ OCP on: Dec 27th, 2011

Database Buffer cache has four states: Pinned: multiple sessions are kept from wirting to same block @ same time. Other session waits to access these blocks Clean : Now the session is unpinned ...

Answered by: saihaan on: Jul 2nd, 2009

Database buffers consists of the dirty blocks. When ever we are trying to update some table/etc. First it verifies whether the data exists in database buffer , If not it fetches the information from d...

What are the components of sga ?

Asked By: Interview Candidate | Asked On: Mar 12th, 2005

Database buffers, redo log buffer the shared pool and   cursors.

Answered by: Nagaraj OCP on: Dec 27th, 2011

SGA has six parts on it

Shared pool
JAVA POOL
Stream Pool
Large Pool
Data Buffer cache - MRU, LRU
Redo log buffer

Answered by: saihaan on: Jul 2nd, 2009

Yes. they are part of SGA. Sharedpool comprises of Library cache and data dictionary cache.

Kernel package

Asked By: kamlesh21 | Asked On: Jun 16th, 2010

Why is Oracle called kernel package?

Answered by: Lokesh M on: Dec 8th, 2011

Oracle introduced the Unbreakable Enterprise Kernel for Oracle Linux during Sep 2010 which runs directly on Oracle LINUX 5 with fast, modern, reliable kernel that is optimized for Oracle software and hardware.

Acid test

Asked By: harsha0544 | Asked On: Jan 3rd, 2010

What is the approach taken by Oracle to pass acid test of a database transaction?

Oracle cluster

Asked By: ajit99 | Asked On: Mar 13th, 2008

What is a cluster and how it is used

Answered by: cmanne on: Sep 2nd, 2009

An Oracle Database Cluster is a set of database instances on different nodes accessing the database related files on a shared storage.

Answered by: shardin on: Oct 19th, 2008

the deployment of a single database across a cluster of servers—providing unbeatable fault tolerance, performance and scalability

What constitute an Oracle instance ?

Asked By: Interview Candidate | Asked On: Sep 6th, 2004

Sga  and  Oracle  background  processes constitute an Oracle instance. (or) combination of memory structure and background process.

Answered by: dj_dj_dj on: Jun 22nd, 2009

Oracle Instance is an combination of background process and memory structures.

Answered by: nareshkumarmca on: Jun 19th, 2009

Oracle instance is the combination of SGA and
background processes.
When user sends a connection request server process starts and it starts instance.

What is the function of checkpoint (ckpt)?

Asked By: Interview Candidate | Asked On: Apr 12th, 2005

The checkpoint (ckpt) process is responsible for signaling  dbwr  at checkpoints  and updating all the data files and control files of the database.

Answered by: gyanudba on: Feb 6th, 2009

Ckpt (checkpoint) is a background process. It synchronize SCNof all the database files likedatafiles, control files and redo log files.

Answered by: taya_ronak on: Feb 2nd, 2009

checkpoint is backgroud process. it'll occur in some situations like during log switch, or on the basis of log_checkpoint_interval or log_checkpoint_timeout parameter in parameter file.  ...

What is sga ?

Asked By: Interview Candidate | Asked On: Sep 6th, 2004

The  system GLobal area (sga) is a shared memory region allocated by Oracle that contains data and control information for one Oracle instance.

Answered by: subhash.terdale on: Oct 1st, 2008

System Global Area (SGA) is component of instance which consist shared memory & control information of the instance
It consist of shared pool, database buffer cached, redo log buffer, large pool, Java pool.

Answered by: Mohammed Abdul Afroze on: Oct 5th, 2007

It is a shared memory region allocated by oracle that contains data and control information for an Oracle Instance. An SGA compromises of Buffer Cache, Redo Log Buffers and Shared Pool Area.

When does dbwr write to the database ?

Asked By: Interview Candidate | Asked On: Sep 6th, 2004

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.

Answered by: subhash.terdale on: Oct 1st, 2008

DBWR writes
* when checkpoint occures
* when dirty buffers reach threshold
* when RAC ping requested
* when free buffers are not available
* when tablespace taken offline,droped

Answered by: sweety on: Apr 26th, 2006

DBWn writes when:

1)checkpoint occurs

2)dirty buffers reach threshold

3)there are no free buffers

4)timeout occurs

5)RAC ping request is made

6)when any tablespace is taken offline,read only,drop or truncated & when begin backup

When does lgwr write to the database ?

Asked By: Interview Candidate | Asked On: Sep 6th, 2004

Lgwr   writes  redo  log  entries  into  an  on-line  redo  log  file  when transactions commit and the log buffer files are full.

Answered by: subhash.terdale on: Oct 1st, 2008

Log writer writes
* when transaction commits
* every three seconds
* when 1/3 of redo full
* when 1mb of redo generated
* before dbwn writes

Answered by: Mohd Israr Khan on: May 24th, 2006

The LGWR   writes  redo  log  entries  into  an  on-line  redo  log  file  when

1. transaction is committed.

2. More than 1 MB of redo log buffer enteries.

3.  1/3 of the redo log buffer is full.

4. Every 3 seconds.

What are the functions of smon ?

Asked By: Interview Candidate | Asked On: Sep 6th, 2004

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...

Answered by: msabuu on: Nov 6th, 2007

If server unplanned shutdown, Power failiure SMON Instant recovery. there is two type of Instant recovery 1st is Roll forward 2nd Roll back.
Rollback means comitted transaction.
Rollforward means uncommitted transaction.

Answered by: msabuu on: Nov 6th, 2007

If server unplanned shutdown, Power failure SMON Instant recovery. there is two type of Instant recovery 1st is Roll forward 2nd Roll back.
Rollback means committed transaction.
Rollforward means uncommitted transaction.

What is shared pool ?

Asked By: Interview Candidate | Asked On: Sep 6th, 2004

Shared  pool is a portion of the sga that contains shared memory constructs such as shared SQL areas.

Answered by: Mohammed Abdul Afroze on: Oct 16th, 2007

Shared Pool compromises of Library Cache and Dictionary Cache.Library Cache stores and shares sql stmts where as plsql stmts in memory.Dictionary Cache: Oracle continously request and update informati...

Answered by: parthokonar on: Apr 19th, 2006

Hi,Actually Shared pool is composed of two parts one is Library Cache and another Data Dictionary cache The Library cache contains the shared sql areas, private sql areas, PL/SQL procedures and packag...

What do redo log buffers contain ?

Asked By: Interview Candidate | Asked On: Sep 6th, 2004

Redo log buffer stores redo entries a log of changes made to the database.

Answered by: Mohammed Abdul Afroze on: Oct 5th, 2007

It stores redo log entries a log of changes made to a Database.

Answered by: Sivamurugesh Arumugam on: Feb 15th, 2007

Redo log buffers consists of change vectors where each vector contains information about which block is changed and where is the change done in the memory. This information will be useful when you are...

What is cursor ?

Asked By: Interview Candidate | Asked On: Sep 6th, 2004

A  cursor is a handle ( a name or pointer) for the memory associated with a specific statement.

Answered by: aloksourav on: Mar 31st, 2007

cursor is nothing but it is temprary storage area.In other word cursor is a private sql work area whenever issuing sql and pl/sql statements ,it creates a memory area in server.this memory area is know as cursor area.

Answered by: Culver_lake on: Mar 28th, 2006

A cursor can be viewed as a "Pointer" into the result table of an SQL SELECT statement. Cursors are needed whenever the result contains more than one row.  3rd generation programs like COBOL and ...

What is shared SQL area ?

Asked By: Interview Candidate | Asked On: Sep 6th, 2004

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.

Answered by: partho sarathi konar on: Oct 1st, 2006

HiShared SQL  areas are shared memory areas; any Oracle process can use a shared SQL area. The use of shared SQL areas reduces memory usage on the database server, thereby increasing system throu...

What does lgwr do ?

Asked By: Interview Candidate | Asked On: Sep 6th, 2004

Log  writer (lgwr) writes redo log entries generated in the redo log buffer of the sga to on-line redo log file.

Answered by: manish hoiyani on: Sep 18th, 2006

LGWR is oracle background process.. all changes which have been made inthe database  gets recorded in the redolog buffer.. so when the users fires an commit statement , LGWR writes these changes ...

Answered by: rajat dey on: Feb 21st, 2006

hi,It is one of the main background process in oracle . In oracle and unix environment you can check this process using ps -ef |pg command . which is writting all the uncommited transaction from SGA to redologfile .regrdsrajat dey

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