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What spfile/init.ora file parameter exists to force the CBO to make the execution path of a given statement use an index, even if the index scan may appear to be calculated as more costly?
Tirumal Devulapalli
- Feb 23rd, 2006
CBO (Cost Based Optimizer):Generates an execution plan for a SQL statementoptimizer_index_cost_adj parameter can be set to help CBO to decide an execution plan, which effects the speed of SQL query.we...
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Database hangs during Package Compile
When the developer trying to compile the package. But the database gets hanged? What will you check?
gogune
- Mar 31st, 2010
Deadlock could have occured. Check whether same object is updated by two sessions.
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Oracle Database Monitoring
If Several databases are up and running, which command will help to monitoring in os ?
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Corrupt Master Database
What do you do when the server cannot start due to a corrupt master database?
rahulniki
- May 9th, 2010
If the master database is corrupt, then surely others also do have the problems and thus the need of MDF recovery comes to an immediate. However you can try out to rebuild it with rebuild.exe and restore it.
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What is the most important action a DBA must perform after changing the database from NOARCHIVELOG TO ARCHIVELOG ?
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Tuning Indicators
What tuning indicators can one use?
prahlad_786
- Jun 25th, 2010
The following high-level tuning indicators can be used to establish if a database is performing optimally or not: • Buffer Cache Hit Ratio Formula: Hit Ratio = (Logical Reads - Physical Read...
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Why and how the deadlock situation arises
If one user is already updating the table and it has a lock, the other user cannot access the table to update. then why and how the deadlock situation arises ?please explain with example.
prahlad_786
- Jun 25th, 2010
When 2 different DML executed on the same resource then it leads to dead lock.Example:If a resource locked by user A and it also need resource which is locked by user B. B also need a ...
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What does a control file contains
gurbux
- Jul 18th, 2010
Control file contains structure and status of the database. It contains database name, datafile and redo log information, SCN number, timestamp of database creation, redo log sequence number.
ramesh khanna
- Jun 27th, 2005
Information about the database,redologfile and datafile,archivelog file location and current scn no and redo log file
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What is the use of redo log information
gurbux
- Jul 18th, 2010
Redo Log Files are used in case of database recovery. As redo logs contain all committed changes made to the data, they are applied from the time database crashes to recover database to point in time.
Amit
- May 7th, 2005
Redo log information are used to recover database if it get currept.
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Troubleshoot SQL * Plus
If the SQL * Plus hangs for a long time, what is the reason?
gurbux
- Jul 19th, 2010
SQL statement is taking long time to retrieve results from database.See which statement is taking longtime by running SELECT * FROM sqltext; or SELECT * from v$session_longops;
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Alert log files
What are four errors found in an alert (error) log that can ruin a DBA's appetite and how can you avoid them?
shaanahmed007
- Aug 3rd, 2010
If we are getting any issue regarding database while performing any activity we should check alert log file in dump destination.1) Snapshot too old error (O1555)2) Deadlock error3) Any issue regarding backup & recovery
brandedfundoo
- Jun 2nd, 2010
I agree..Deadlock error: Oracle takes care by itself. No damageSnapshot error: Rerun query. No damageOra-00600 : Internal.. very critical. Though directly Oracle has to be involved in resolution, stil...
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How to DROP an Oracle Database?
You can do it at the OS level by deleting all the files of the database. The files to be deleted can be found using: 1) select * from dba_data_files; 2) select * from v$logfile; 3) select * from v$controlfile; 4) archive log list 5) initSID.ora 6) In addition you can clean the UDUMP, BDUMP, scripts etc Clean up the listener.ora and the tnsnames.ora. make sure that the oratab entry is also removed.
ianilreddy
- Aug 7th, 2010
Start the database with startup mount restrictthen drop the database using drop database command.
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Restricted Mode Memory Gap
How to check to memory gap once the SGA is started in Restricted mode?
sonaligujral1
- Aug 7th, 2010
No memory gap would occur whether database is started in open or restricted mode.
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Database Auto extend question
This is an Interview Question By BMC Software.. " while installing the Oracle 9i ( 9.2) version, automatically system takes the space of approximately 4 GB.. thats fine.... Now, if my database is growing up and it is reaching the 4GB of my database space...Now, i would like to extend my Database space to 20 GB or 25 GB... what are the things i have to do " Pls give me the accurate Solutions or alternates...
alex.v
- Jul 11th, 2008
Better make the autoextend off and add more datafiles to the tablespace. Making a single datafile to a bigger size is risky...By making autoextend off you can monitor the growth of the tablespace....schedule a growth monitoring script with a threshhold of 85 % full
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Changed Performance
When yesterday developer gives the following command: select count(*) from [table name]it gives the output within minutes, today the same command takes hours? What will you check?
vijender reddy
- Aug 13th, 2010
First we must check for any locks on the objects, if we get any locks then just release that lock.Here is how you can know if there is a lock on an object1. Find sidSQL>select distinct sid from v$...
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Oracle Backsets created by RMAN
Can you use Backsets created by RMAN with any other utility
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How are the index updates
alvinstars
- Sep 7th, 2010
The database automatically maintains and uses indexes after they are created. The database also automatically reflects changes to data, such as adding, updating, and deleting rows, in all relevant indexes with no additional actions required by users.
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DB Server Performance Bottlenecks
What are four performance bottlenecks that can occur in a database server and How are they detected?
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Db_buffercache tuning
Db_buffercache : How we will tune it.
dbashashi
- Dec 2nd, 2010
You can take advantage of db_cache_advice in the parameter file. you can also use v$db_cache_advice.When using db_cache_advice = On; a proper caution is adviced as it can take some memory from Shared_pool will be affected which otherwise meant for same purpose
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Oracle DB Buffer Cache
How the data is processed in DB Buffer Cache.
dbashashi
- Dec 2nd, 2010
Hi,Db_buffer_Cache is nothing but a memory allocated out of physical Memory (RAM) and is part of SGA.When the database server starts for the first time the DB_buffer_cache doesnt have any information ...
Oracle DBA Interview Questions
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