301. What is a Shared SQL pool?
The data dictionary cache is stored in an area in SGA called the Shared SQL Pool. This will allow sharing of parsed SQL statements among concurrent users.
302. What is hot backup and how it can be taken?
Taking backup of archive log files when database is open. For this the ARCHIVELOG mode should be enabled. The following files need to be backed up. All data files. All Archive log, redo log files. All
control files.
303. List the Optional Flexible Architecture (OFA) of Oracle database? or How can we organize the tablespaces in Oracle database to have maximum performance ?
SYSTEM - Data dictionary tables.
DATA - Standard operational tables.
DATA2- Static tables used for standard operations
INDEXES - Indexes for Standard operational tables.
INDEXES1 - Indexes of static tables used for standard operations.
TOOLS - Tools table.
TOOLS1 - Indexes for tools table.
RBS - Standard Operations Rollback Segments,
RBS1,RBS2 - Additional/Special Rollback segments.
TEMP - Temporary purpose tablespace
TEMP_USER - Temporary tablespace for users.
USERS - User tablespace.
304. How to implement the multiple control files for an existing database ?
Shutdown the database Copy one of the existing control file to new location Edit Config ora file by adding new control file. name Restart the database.
305. What is advantage of having disk shadowing/ Mirroring ?
Shadow set of disks save as a backup in the event of disk failure.
In most Operating System if any disk failure occurs it automatically switchover to place of failed disk. Improved performance because most OS support volume shadowing can direct file I/O request to use
the shadow set of files instead of the main set of files. This reduces I/O load on the main set of disks.
306. How will you force database to use particular rollback segment ?
SET TRANSACTION USE ROLLBACK SEGMENT rbs_name.
307. Why query fails sometimes ?
Rollback segment dynamically extent to handle larger transactions entry loads. A single transaction may wipeout all available free space in the Rollback Segment Tablespace. This prevents other user
using Rollback segments.
308. What is the use of RECORD LENGTH option in EXP command ?
Record length in bytes.
309. How will you monitor rollback segment status ?
Querying the DBA_ROLLBACK_SEGS view
IN USE - Rollback Segment is on-line.
AVAILABLE - Rollback Segment available but not on-line.
OFF-LINE - Rollback Segment off-line
INVALID - Rollback Segment Dropped.
NEEDS RECOVERY - Contains data but need recovery or corupted.
PARTLY AVAILABLE - Contains data from an unresolved transaction involving a distributed database.
310. What is meant by Redo Log file mirroring ? How it can be achieved?
Process of having a copy of redo log files is called mirroring. This
can be achieved by creating group of log files together, so that
LGWR will automatically writes them to all the members of the
current on-line redo log group. If any one group fails then database
automatically switch over to next group. It degrades performance.
311. Which parameter in Storage clause will reduce no. of rows per block?
PCTFREE parameter
Row size also reduces no of rows per block.
312. What is meant by recursive hints ?
Number of times processes repeatedly query the dictionary table is
called recursive hints. It is due to the data dictionary cache is
too small. By increasing the SHARED_POOL_SIZE parameter we can
optimize the size of Data Dictionary Cache.
313. What is the use of PARFILE option in EXP command ?
Name of the parameter file to be passed for export.
314. What is the use of PARFILE option in EXP command ?
Name of the parameter file to be passed for export.
315. What is a logical backup?
Logical backup involves reading a set of database records and writing them into a file. Export utility is used for taking backup and Import utility is used to recover from backup.
316. What is the use of TABLES option in EXP command ?
List of tables should be exported.ze)
317. What is the OPTIMAL parameter?
It is used to set the optimal length of a rollback segment.
318. What is a Rollback segment entry ?
It is the set of before image data blocks that contain rows that are modified by a transaction. Each Rollback Segment entry must be completed within one rollback segment. A single rollback segment can have multiple rollback segment entries.
319. What is mean by Program Global Area (PGA) ?
It is area in memory that is used by a Single Oracle User Process.
320. What is hit ratio ?
It is a measure of well the data cache buffer is handling requests for data.
Hit Ratio = (Logical Reads - Physical Reads - Hits Misses)/ Logical Reads.
321. What are the different kind of export backups?
Full back - Complete database
Incremental - Only affected tables from last incremental date/full backup date.
Cumulative backup - Only affected table from the last cumulative date/full backup date.
322. How free extents are managed in Ver 6.0 and Ver 7.0 ?
Free extents cannot be merged together in Ver 6.0.
Free extents are periodically coalesces with the neighboring free extent in Ver 7.0
323. What is the use of RECORD option in EXP command?
For Incremental exports, the flag indirects whether a record will be stores data dictionary tables recording the export.
324. What is the use of ROWS option in EXP command ?
Flag to indicate whether table rows should be exported. If 'N' only DDL statements for the database objects will be created.
325. What is the use of COMPRESS option in EXP command ?
Flag to indicate whether export should compress fragmented segments into single extents.
326. How will you swap objects into a different table space for an existing database ?
Export the user
Perform import using the command imp system/manager file=export.dmp indexfile=newrite.sql.
This will create all definitions into newfile.sql. Drop necessary objects.
Run the script newfile.sql after altering the tablespaces.
Import from the backup for the necessary objects.
327. How does Space allocation table place within a block ?
Each block contains entries as follows
Fixed block header
Variable block header
Row Header,row date (multiple rows may exists)
PCTEREE (% of free space for row updation in future)
328. What are the factors causing the reparsing of SQL statements in SGA?
Due to insufficient Shared SQL pool size. Monitor the ratio of the reloads takes place while executing SQL statements. If the ratio is greater than 1 then increase the SHARED_POOL_SIZE. LOGICAL &
PHYSICAL ARCHITECTURE OF DATABASE.
329. What is dictionary cache ?
Dictionary cache is information about the databse objects stored in a data dictionary table.
330. What is a Control file ?
Database overall physical architecture is maintained in a file called control file. It will be used to maintain internal consistency and guide recovery operations. Multiple copies of control files are advisable.
331. What is Database Buffers ?
Database buffers are cache in the SGA used to hold the data blocks that are read from the data segments in the database such as tables, indexes and clusters DB_BLOCK_BUFFERS parameter in INIT.ORA decides the size.
332. How will you create multiple rollback segments in a database ?
Create a database which implicitly creates a SYSTEM Rollback Segment in a SYSTEM tablespace. Create a Second Rollback Segment name R0 in the SYSTEM tablespace. Make new rollback segment available (After shutdown, modify init.ora file and Start database) Create other tablespaces (RBS) for rollback segments. Deactivate Rollback Segment R0 and activate the newly created rollback segments.
333. What is cold backup? What are the elements of it?
Cold backup is taking backup of all physical files after normal shutdown of database.
We need to take.
- All Data files.
- All Control files.
- All on-line redo log files.
- The init.ora file (Optional)
334. What is meant by redo log buffer ?
Changes made to entries are written to the on-line redo log files. So that they can be used in roll forward operations during database recoveries. Before writing them into the redo log files, they will
first brought to redo log buffers in SGA and LGWR will write into files frequently. LOG_BUFFER parameter will decide the size.
335. How will you estimate the space required by a non-clustered tables?
Calculate the total header size
Calculate the available dataspace per data block
Calculate the combined column lengths of the average row
Calculate the total average row size.
Calculate the average number rows that can fit in a block
Calculate the number of blocks and bytes required for the table.
After arriving the calculation, add 10 % additional space to
calculate the initial extent size for a working table.
336. How will you monitor the space allocation ?
By querying DBA_SEGMENT table/view.
337. What is meant by free extent ?
A free extent is a collection of continuous free blocks in tablespace. When a segment is dropped its extents are reallocated and are marked as free.
338. What is the use of IGNORE option in IMP command ?
A flag to indicate whether the import should ignore errors encounter when issuing CREATE commands.
339. What is the use of ANALYSE ( Ver 7) option in EXP command ?
A flag to indicate whether statistical information about the exported objects should be written to export dump file.
340. What is the use of ROWS option in IMP command ?
A flag to indicate whether rows should be imported. If this is set to 'N' then only DDL for database objects will be executed.
341. What is the use of INDEXES option in EXP command ?
A flag to indicate whether indexes on tables will be exported.
A flag to indicate whether import should import index on tables or not.
343. What is the use of GRANT option in EXP command?
A flag to indicate whether grants on databse objects will be exported or not. Value is 'Y' or 'N'.
344. What is the use of GRANT option in IMP command ?
A flag to indicate whether grants on database objects will be imported.
345. What is the use of FULL option in EXP command ?
A flag to indicate whether full databse export should be performed.
346. What is the use of SHOW option in IMP command ?
A flag to indicate whether file content should be displayed or not.
347. What is the use of CONSTRAINTS option in EXP command ?
A flag to indicate whether constraints on table need to be exported.
348. What is the use of CONSISTENT (Ver 7) option in EXP command ?
A flag to indicate whether a read consistent version of all the exported objects should be maintained.
349. What are the different methods of backing up oracle database ?
- Logical Backups
- Cold Backups
- Hot Backups (Archive log)
350. What is the difference between ON-VALIDATE-FIELD trigger and a POST-CHANGE trigger ?
When you changes the Existing value to null, the On-validate field trigger will fire post change trigger will not fire. At the time of execute-query post-change trigger will fire, on-validate field trigger will not fire.
