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Oracle Enterprise Manager OEM in LINUX (Video)1


Oracle Enterprise Manager OEM  in LINUX
 OEM Configuration and Installation in details


Oracle 12C New Features

 The Oracle 12C means different things to different people. It all depends on which areas you are looking at, as there are improvements in many areas. Summarized below is the list of Top 12 Features of Oracle 12C as I see it. I have summarized below, the top 12 which I found interesting.


01. Pluggable Databases Through Database Consolidation:

Oracle is doing every thing to jump into the cloud bandwagon. With 12C, Oracle is trying to address the problem of Multitenancy through this feature. There is a radical change and a major change in the core database architecture through the introduction of Container Databases also called CBD and Pluggable Databases (PDB). The memory and process is owned by the Container Database. The container holds the metadata where the PDBs hold the user data. You can create upto 253 PDBs including the seed PDB.
In a large setup, it is common to see 20 or 30 different instances running in production environment. With these many instances, it is a maintenance nightmare as all these instances have to be separately
•Upgraded
•Patched
•Monitored
•Tuned
•RAC Enabled
•Adjusted
•Backed up and 
•Data Guarded.

With Pluggable Databases feature, you just have to do all this for ONE single instance. Without this feature, prior to 12C, you would have to create separate schemas and there is always a thread of security how much ever the isolation we build into it. There are problems with namespace conflicts, there is always going to be one public synonym that you can create. With PDBs you can have a separate HR or Scott schema for each PDB, separate Emp, Dept Tables and separate public synonyms. Additionally, 2 PDBs can talk to each other through the regular DB Link feature. There is no high startup cost of creating a database any more. Instead of one instance per day, the shift is into one instance per many databases. For the developer community, you can be oblivious of all this and still continue to use the PDBs as if it were a traditional database, but for the DBAs the world would look like it has changed a lot.
Another cool feature is, you can allocate a CPU percentage for each PDB.
Another initiative being, it has announced a strategic tieup with salesforce.com during the first week of July 2013.

02. Redaction Policy:

This is one of the top features in Oracle 12C. Data Redaction in simple terms means, masking of data. You can setup a Data Redaction policy, for example SSN field in a Employee table can be masked. This is called redaction. From Sql Develop you can do this by going to the table: Employee->Right click on Security Policy->click on New->click on Redaction Policy->Enter SSN. 
When you do a select * from employee, it will show that the SSN is masked.
The new data masking will use a package called DBMS_REDACT. It is the extension to the FGAC and VPD present in earlier versions.
By doing this, whoever needs to view the data will be able to see it where as the other users will not be able to view it.

03. Top N Query and Fetch and offset Replacement to Rownum:

With the release of Oracle Database 12c, Oracle has introduced this new SQL syntax to simplify fetching the first few rows. The new sql syntax "Fetch First X Rows only" can be used.

04. Adaptive Query Optimization and Online Stats Gathering:

With this feature, it helps the optimizer to make runtime adjustments to execution plan which leads to better stats. For statements like CTAS (Create Table As Select) and IAS (Insert As Select), the stats is gathered online so that it is available immediately.

05. Restore a Table easily through RMAN:

Earlier if you had to restore a particular table, you had to do all sorts of things like restoring a tablespace and or do Export and Import. The new restore command in RMAN simplifies this task.

06. Size Limit on Varchar2, NVarchar2, Raw Data Types increased:

The previous limit on these data types was 4K. In 12C, it has been increased to 32,767 bytes. Upto 4K, the data is stored inline. I am sure everyone will be happy with this small and cute enhancement.

07. Inline PL/SQL Functions and Procedures:

The in line feature is extended in Oracle 12C. In addition to Views, we can now have PL/SQL Procedures and Functions as in line constructs. The query can be written as if it is calling a real stored procedure, but however the functions do not actually exist in the database. You will not be able to find them in ALL_OBJECTS. I think this will be a very good feature for the developers to explore as there is no code that needs to be compiled.

08. Generated as Identity/Sequence Replacement:

You can now create a col with 'generated as identity' clause. Thats it. Doing this is equivalent to creating a separate sequence and doing a sequence.nextval for each row. This is another handy and a neat feature which will help developer community. This is also called No Sequence Auto Increment Primary Key.

09. Multiple Indexes on a Single Column:

Prior to 12C, a column cant be in more than one index. In 12C, you can include a column in B-tree index as well as a Bit Map index. But, please note that only one index is usable at a given time.

10. Online Migration of Table Partition or Sub Partition:

You can very easily migrate a partition or sub partition from one tablespace to another. Similar to how the online migration was achieved for a non-partitioned table in prior releases, a table partition or sub partition can be moved to another tablespace online or offline. When an ONLINE clause is specified, all DML operations can be performed without any interruption on the partition|sub-partition which is involved in the procedure. In contrast, no DML operations are allowed if the partition|sub-partition is moved offline.

11. Temporary UNDO:

Prior to 12C, undo records generated by TEMP Tablespace is stored in the undo tablespace. With Temp undo feature in 12C, temp undo records can be stored in temporary table instead of UNDO TS. The benefit is - reduced undo tablespace and reduced redo log space used.
SQL> ALTER SYSTEM SET PGA_AGGREGATE_LIMIT=2G;
SQL> ALTER SYSTEM SET PGA_AGGREGATE_LIMIT=0; --disables the hard limit

12. In Database Archiving:

This feature enables archiving rows within a table by marking them as inactive. These inactive rows are in the database and can be optimized using compression but are not visible to the application. These records are skipped during FTS (Full Table Scan).

Other Features:

Advanced Replication and Streams are Dead. It is being replaced with Oracle Golden Gate.
Invisible Columns. You can now have a invisible column in a table. When a column is defined as invisible, the column won’t appear in generic queries
PGA Aggregate Limit setting:
In 12c, you can set a hard limit on PGA by enabling the automatic PGA management, which requires PGA_AGGREGATE_LIMIT parameter settings. Therefore, you can now set the hard limit on PGA by setting the new parameter to avoid excessive PGA usage.
DDL Logging:
The DDL statements will automatically get recorded in xml/log file if ENABLE_DDL_LOGGING is set to True. ALTER SYSTEM|SESSION SET ENABLE_DDL_LOGGING=TRUE



Installing Oracle Database and Creating a Database(Linux) OS


  1. Log on to your computer as a member of the administrative group that is authorized to install Oracle Database software and to create and run the database.
    Refer to your operating system-specific documentation or contact your system administrator to determine whether you have the necessary privileges and permissions to install new software.
  2. Do one of the following:
    • If you are installing from distribution media, then insert the distribution media for the database into your computer.
      The Autorun feature opens the Select a Product to Install window automatically.
    • If you downloaded the installation software from the Oracle Web site, then follow the instructions on the site to run the Oracle Universal Installer. Or, see the Oracle Database Installation Guide for your platform.
  3. The first window that appears is the Configure Security Updates window. To receive notifications about security issues via e-mail, enter your e-mail address in the Email text field. To receive security updates from My Oracle Support, enter the e-mail address registered with My Oracle Support, select the I wish to receive security updates... option, and enter your My Oracle Support password.
    Click Next to continue.
    The Select Installation Option window appears.
  4. Choose the Create and configure a database option. Or, you also have the option of choosing to only install the database software, but then you must create a database in an additional step after the software is installed. If you are currently using a previous version of Oracle Database, choose Upgrade an existing database. After you have chosen an option, click Next.
    The System Class window appears.
  5. Choose Desktop Class.
    You can choose the Server Class option to customize your installation. For example, you use this method to configure Oracle Automatic Storage Management for your database, install the Sample Schemas, or configure automated backups. Selecting this option guides you through a series of installation steps that are not documented in this guide. For more information about the advanced choices, see "About Advanced Installation". Also see Oracle Database Installation Guide for your platform.
    Click Next.
    The Typical Install Configuration window appears.
    Description of install_basic.gif follows

  6. Provide the following configuration details for the database:
    • Oracle Base Location— The Oracle base directory helps to facilitate the organization of multiple Oracle software installations. See the Oracle Database Installation Guide for your platform for more information about ORACLE_BASE.
      If you did not set the ORACLE_BASE environment variable before starting OUI, then the Oracle base directory is created in anapp/username/directory on the first existing and writable directory from /u01 through /u09 for UNIX and Linux systems, or on the disk drive with the most available space for Windows systems. If /u01 through /u09 does not exist on the UNIX or Linux system, then the default location is user_home_directory/app/username.
      You can click Browse to find the directory you want to act as the Oracle base directory.
    • Software Location—The software location is the Oracle home for your database. You must specify a new Oracle home directory for each new installation of Oracle Database software. By default, the Oracle home directory is a subdirectory of the Oracle base directory.
      You can click Browse to find the directory where you want to install the Oracle Database software.
    • Database File Location—The database file location is the location where Oracle Database files are stored. By default, this location is Oracle_base/oradata. You can click Browse to select a different location.
    • Database Edition—Select either Enterprise EditionStandard EditionStandard Edition One, or Personal Edition (Microsoft Windows platforms only). See "Installation Type".
    • Character Set—Choose the character set to use to store the data within the database. You can choose between the Default, which is based on the operating system language settings, or Unicode.
    • OSDBA Group (Linux and UNIX platforms only)—Specify the operating system DBA group. Host computer users in this group have administrative privileges on the database. This group is typically named dba. Refer to Oracle Database Installation Guide for Linuxor for your UNIX platform for more details.
    • Global Database Name—Enter the fully qualified global database name. See "Installation Type" for more on global database name.
    • Administrative Password—Specify the initial password for the SYSSYSTEMSYSMAN, and DBSNMP administrator accounts. If the password you choose is not a secure password, a warning message will be displayed.
    After you enter the required information, click Next.
    If Oracle software has not previously been installed on this server, then the Create Inventory window appears. If this is not the first installation attempt on this server, then the Perform Prerequisite Checks window appears.
  7. For first time installations on Linux and UNIX operating systems only, specify a directory for installation files and the name of an operating system group that has write permissions for that directory.
    If this is the first time you are installing any Oracle software on this computer, then the Create Inventory Directory window appears. You must specify a local directory for the inventory, which OUI uses to keep track of all Oracle software installed on the computer. This information is used while applying patches or upgrading an existing installation, and while deinstalling Oracle software. Note that this directory is different from the Oracle home directory. The recommended value for the inventory directory isOracle_base/../oraInventory, or one level above the Oracle base directory, in the oraInventory subdirectory. If your Oracle base directory is /u01/app/oracle, then the Oracle inventory directory defaults to /u01/app/oraInventory.
    In this window you can also specify the operating system group that has write permissions on the inventory directory. This prevents other users from writing over the Oracle product installation files. Typically the oinstall group is selected.
    After you enter a directory path and optionally specify an operating system group, click Next to continue.
    The Perform Prerequisite Checks window appears.
  8. If any checks failed, then take corrective actions.
    OUI performs several environment checks and indicates whether the check was a success, or resulted in a warning or failure. Details of the checks are provided in the displayed window. The installation can proceed only when all checks have a status of either Succeeded or Warning. If any of the environment checks failed, then they must be resolved manually. See "Checking Prerequisites" for more information.
    If all the prerequisite checks passed, or after you click Next, the Summary window appears,
  9. Review the installation summary, then click Finish to start the installation.
    The Install window appears, showing the installation progress. After the installation phase, the Configuration Assistants window appears. This window lists the configuration assistants that are started automatically. If you chose to create a starter database, then Database Configuration Assistant starts automatically in a separate window.
    After database creation, a window is displayed that summarizes the database creation.
  10. (Optional) Click Password Management to unlock user accounts to make the accounts accessible to users.
    The SYS and SYSTEM accounts are unlocked by default.
  11. Click OK to continue the installation.
  12. For Linux and UNIX operating systems only, run the specified scripts, then click OK.
    In the Execute Configuration Scripts window, you are prompted to open a new terminal window, and to run scripts as the root user. After you run the scripts, return to this window and click OK.
  13. Make note of the information in the Finish window, then click Close to exit OUI.
    Your installation and database creation is now complete. The Finish window displays one or more important URLs, including one for the Oracle Enterprise Manager Database Control console. (The console is the user interface—the Web application—portion of Oracle Enterprise Manager Database Control.)
    You use Oracle Enterprise Manager Database Control to perform common database administration tasks. The URL and port information for Database Control can be found after installation in the Oracle_home/install/portlist.ini file.



DBA Interview Questions 3

What is Row Migration and Row Chaining?
There are two circumstances when this can occur, the data for a row in a table may be too large to fit into a single data block. This can be caused by either row chaining or row migration.
Chaining: Occurs when the row is too large to fit into one data block when it is first inserted. In this case, Oracle stores the data for the row in a chain of data blocks (one or more) reserved for that segment. Row chaining most often occurs with large rows, such as rows that contain a column of data type LONG, LONG RAW, LOB, etc. Row chaining in these cases is unavoidable.
Migration: Occurs when a row that originally fitted into one data block is updated so that the overall row length increases, and the block’s free space is already completely filled. In this case, Oracle migrates the data for the entire row to a new data block, assuming the entire row can fit in a new block. Oracle preserves the original row piece of a migrated row to point to the new block containing the migrated row: the rowid of a migrated row does not change. When a row is chained or migrated, performance associated with this row decreases because Oracle must scan more than one data block to retrieve the information for that row.
  1. INSERT and UPDATE statements that cause migration and chaining perform poorly, because they perform additional processing.
  2. SELECTs that use an index to select migrated or chained rows must perform additional I/Os.
Detection: Migrated and chained rows in a table or cluster can be identified by using the ANALYZE command with the LIST CHAINED ROWS option. This command collects information about each migrated or chained row and places this information into a specified output table. To create the table that holds the chained rows,
execute script UTLCHAIN.SQL.
SQL> ANALYZE TABLE scott.emp LIST CHAINED ROWS;
SQL> SELECT * FROM chained_rows;
You can also detect migrated and chained rows by checking the ‘table fetch continued row’ statistic in the v$sysstat view.
SQL> SELECT name, value FROM v$sysstat WHERE name = ‘table fetch continued row’;
Although migration and chaining are two different things, internally they are represented by Oracle as one. When detecting migration and chaining of rows you should analyze carefully what you are dealing with.
What is Ora-01555 - Snapshot Too Old error and how do you avoid it?
1. Increase the size of rollback segment. (Which you have already done)
2. Process a range of data rather than the whole table.
3. Add a big rollback segment and allot your transaction to this RBS.
4. There is also possibility of RBS getting shrunk during the life of the query by setting optimal.
5. Avoid frequent commits.
6. Google out for other causes.
What is a locally Managed Tablespace?
A Locally Managed Tablespace is a tablespace that manages its own extents maintaining a bitmap in each data file to keep track of the free or used status of blocks in that data file. Each bit in the bitmap corresponds to a block or a group of blocks. When the extents are allocated or freed for reuse, Oracle changes the bitmap values to show the new status of the blocks. These changes do not generate rollback information because they do not update tables in the data dictionary (except for tablespace quota information), unlike the default method of Dictionary - Managed Tablespaces.
Following are the major advantages of locally managed tablespaces –
• Reduced contention on data dictionary tables 
• No rollback generated 
• No coalescing required 
• Reduced recursive space management.
Can you audit SELECT statements?
      Yes, we can audit the select statements. Check out the below example:
SQL> show parameter audit
NAME TYPE VALUE
———————————— ———– ——————————
audit_file_dest string E:\ORACLE\PRODUCT\10.2.0\DB_2\
ADMIN\SRK\ADUMP
audit_sys_operations boolean FALSE
audit_trail string NONE
SQL>  begin
dbms_fga.add_policy ( object_schema => ‘SCOTT’,
object_name => ‘EMP2′,
policy_name => ‘EMP_AUDIT’,
statement_types => ‘SELECT’ );
end;
/
PL/SQL procedure successfully completed.
SQL>select * from dba_fga_audit_trail;
             no rows selected
In HR schema:
SQL> create table bankim(
name varchar2 (10),
roll number (20));
Table created.
SQL> insert into bankim values (‘bankim’, 10);
1 row created.
SQL> insert into bankim values (‘bankim2′, 20);
1 row created.
SQL> select * from bankim;
NAME ROLL
———- ———-
bankim 10
bankim2 20
SQL> select name from bankim;
NAME
———-
bankim
bankim2
In sys schema:
SQL>set head off
SQL> select sql_text from dba_fga_audit_trail;
select count(*) from emp2
select * from emp2
select * from emp3
select count(*) from bankim
select * from bankim
select name from bankim
What does DBMS_FGA package do?
The dbms_fga Package is the central mechanism for the FGA is implemented in the package dbms_fga, where all the APIs are defined. Typically, a user other than SYS is given the responsibility of maintaining these policies. With the convention followed earlier, we will go with the user SECUSER, who is entrusted with much of the security features. The following statement grants the user SECUSER enough authority to create and maintain the auditing facility.
Grant execute on dbms_fga to secuser;
The biggest problem with this package is that the polices are not like regular objects with owners. While a user with execute permission on this package can create policies, he or she can drop policies created by another user, too. This makes it extremely important to secure this package and limit the use to only a few users who are called to define the policies, such as SECUSER, a special user used in examples.
What is Cost Based Optimization?
The CBO is used to design an execution plan for SQL statement. The CBO takes an SQL statement and tries to weigh different ways (plan) to execute it. It assigns a cost to each plan and chooses the plan with smallest cost.
The cost for smallest is calculated: Physical IO + Logical IO / 1000 + net IO.
How often you should collect statistics for a table?
CBO needs some statistics in order to assess the cost of the different access plans. These statistics includes:
Size of tables, Size of indexes, number of rows in the tables, number of distinct keys in an index, number of levels in a B* index, average number of blocks for a value, average number of leaf blocks in an index
These statistics can be gathered with dbms_stats and the monitoring feature.
How do you collect statistics for a table, schema and Database?
Statistics are gathered using the DBMS_STATS package. The DBMS_STATS package can gather statistics on table and indexes, and well as individual columns and partitions of tables. When you generate statistics for a table, column, or index, if the data dictionary already contains statistics for the object, then Oracle updates the existing statistics. The older statistics are saved and can be restored later if necessary. When statistics are updated for a database object, Oracle invalidates any currently parsed SQL statements that access the object. The next time such a statement executes, the statement is re-parsed and the optimizer automatically chooses a new execution plan based on the new statistics.
Collect Statistics on Table Level
sqlplus scott/tiger
exec dbms_stats.gather_table_stats ( -
     ownname          => 'SCOTT', -
     tabname          => 'EMP', -
     estimate_percent => dbms_stats.auto_sample_size, -
     method_opt       => 'for all columns size auto', -
     cascade          => true, -
     degree           => 5 - )
/
Collect Statistics on Schema Level
sqlplus scott/tiger
exec dbms_stats.gather_schema_stats ( -
     ownname          => 'SCOTT', -
     options          => 'GATHER', -
     estimate_percent => dbms_stats.auto_sample_size, -
     method_opt       => 'for all columns size auto', -
     cascade          => true, -
     degree           => 5 - )

Collect Statistics on Other Levels
DBMS_STATS can collect optimizer statistics on the following levels, see Oracle Manual
GATHER_DATABASE_STATS
GATHER_DICTIONARY_STATS
GATHER_FIXED_OBJECTS_STATS
GATHER_INDEX_STATS
GATHER_SCHEMA_STATS
GATHER_SYSTEM_STATS
GATHER_TABLE_STATS
Can you make collection of Statistics for tables automatic?
Yes, you can schedule your statistics but in some situation automatic statistics gathering may not be adequate. It suitable for those databases whose object is modified frequently. Because the automatic statistics gathering runs during an overnight batch window, the statistics on tables which are significantly modified during the day may become stale.
There may be two scenarios in this case:                           
·         Volatile tables that are being deleted or truncated and rebuilt during the course of the day.
·         Objects which are the target of large bulk loads which add 10% or more to the object’s total size.
So you may wish to manually gather statistics of those objects in order to choose the optimizer the best execution plan. There are two ways to gather statistics.
  1. Using DBMS_STATS package.
  2. Using ANALYZE command
How can you use ANALYZE statement to collect statistics?
ANALYZE TABLE emp ESTIMATE STATISTICS FOR ALL COLUMNS;
ANALYZE INDEX inv_product_ix VALIDATE STRUCTURE;
ANALYZE TABLE customers VALIDATE REF UPDATE;
ANALYZE TABLE orders LIST CHAINED ROWS INTO chained_rows;
ANALYZE TABLE customers VALIDATE STRUCTURE ONLINE;
To delete statistics:
ANALYZE TABLE orders DELETE STATISTICS;
To get the analyze details:
SELECT owner_name, table_name, head_rowid, analyze_timestamp FROM chained_rows;
On which columns you should create Indexes?
The following list gives guidelines in choosing columns to index:
  • You should create indexes on columns that are used frequently in WHERE clauses.
  • You should create indexes on columns that are used frequently to join tables.
  • You should create indexes on columns that are used frequently in ORDER BY clauses.
  • You should create indexes on columns that have few of the same values or unique values in the table.
  • You should not create indexes on small tables (tables that use only a few blocks) because a full table scan may be faster than an indexed query.
  • If possible, choose a primary key that orders the rows in the most appropriate order.
  • If only one column of the concatenated index is used frequently in WHERE clauses, place that column first in the CREATE INDEX statement.
  • If more than one column in a concatenated index is used frequently in WHERE clauses, place the most selective column first in the CREATE INDEX statement.
What type of Indexes is available in Oracle?
  • B-tree indexes: the default and the most common.
  • B-tree cluster indexes: defined specifically for cluster.
  • Hash cluster indexes: defined specifically for a hash cluster.
  • Global and local indexes: relate to partitioned tables and indexes.
  • Reverse key indexes: most useful for Oracle Real Application Clusters.
  • Bitmap indexes: compact; work best for columns with a small set of values
  • Function-based indexes: contain the pre-computed value of a function/expression Domain indexes: specific to an application or cartridge.
What is B-Tree Index?
B-Tree is an indexing technique most commonly used in databases and file systems where pointers to data are placed in a balance tree structure so that all references to any data can be accessed in an equal time frame. It is also a tree data structure which keeps data sorted so that searching, inserting and deleting can be done in logarithmic amortized time.
A table is having few rows, should you create indexes on this table?
You should not create indexes on small tables (tables that use only a few blocks) because a full table scan may be faster than an indexed query.
A Column is having many repeated values which type of index you should create on this column
B-Tree index is suitable if the columns being indexed are high cardinality (number of repeated values). In fact for this situation a bitmap index is very useful but bitmap index are vary expensive.
When should you rebuild indexes?
There is no thumb rule “when you should rebuild the index”. According to expert it depends upon your database situation:
When the data in index is sparse (lots of holes in index, due to deletes or updates) and your query is usually range based or If Blevel >3 then takes index in rebuild consideration; desc DBA_Indexes;
Because when you rebuild indexes then database performance goes down.
In fact binary tree index can never be unbalanced. Binary tree performance is good for both small and large tables and does not degrade with the growth of table.
Can you build indexes online?
Yes, we can build index online. It allows performing DML operation on the base table during index creation. You can use the statements:
CREATE INDEX ONLINE and DROP INDEX ONLINE.
ALTER INDEX REBUILD ONLINE is used to rebuild the index online.
A Table Lock is required on the index base table at the start of the CREATE or REBUILD process to guarantee DDL information. A lock at the end of the process also required to merge change into the final index structure.
A table is created with the following setting
                storage (initial 200k
                   next 200k
                   minextents 2
                   maxextents 100
                   pctincrease 40)
What will be size of 4th extent?
Percent Increase allows the segment to grow at an increasing rate.
The first two extents will be of a size determined by the Initial and Next parameter (200k)
The third extent will be 1 + PCTINCREASE/100 times the second extent (1.4*200=280k).
AND the 4th extent will be 1 + PCTINCREASE/100 times the third extent (1.4*280=392k!!!) and so on...
Can you Redefine a table Online?
Yes. We can perform online table redefinition with the Enterprise Manager Reorganize Objects wizard or with the DBMS_REDEFINITION package.
It provides a mechanism to make table structure modification without significantly affecting the table availability of the table. When a table is redefining online it is accessible to both queries and DML during the redefinition process.
Purpose for Table Redefinition
·         Add, remove, or rename columns from a table
·         Converting a non-partitioned table to a partitioned table and vice versa
·         Switching a heap table to an index organized and vice versa
Modifying storage parameters
·         Adding or removing parallel support
·         Reorganize (defragmenting) a table
·         Transform data in a table
Restrictions for Table Redefinition:
·         One cannot redefine Materialized Views (MViews) and tables with MViews or MView Logs defined on them.
·         One cannot redefine Temporary and Clustered Tables
·         One cannot redefine tables with BFILE, LONG or LONG RAW columns
·         One cannot redefine tables belonging to SYS or SYSTEM
·         One cannot redefine Object tables
·         Table redefinition cannot be done in NOLOGGING mode (watch out for heavy archiving)
·         Cannot be used to add or remove rows from a table
Can you assign Priority to users?
Yes, we can do this through resource manager. The Database Resource Manager gives a database administrators more control over resource management decisions, so that resource allocation can be aligned with an enterprise's business objectives.
With Oracle database Resource Manager an administrator can:
  • Guarantee certain users a minimum amount of processing resources regardless of the load on the system and the number of users
  • Distribute available processing resources by allocating percentages of CPU time to different users and applications.
  • Limit the degree of parallelism of any operation performed by members of a group of users
  • Create an active session pool. This pool consists of a specified maximum number of user sessions allowed to be concurrently active within a group of users. Additional sessions beyond the maximum are queued for execution, but you can specify a timeout period, after which queued jobs terminate.
  • Allow automatic switching of users from one group to another group based on administrator-defined criteria. If a member of a particular group of users creates a session that runs for longer than a specified amount of time, that session can be automatically switched to another group of users with different resource requirements.
  • Prevent the execution of operations that are estimated to run for a longer time than a predefined limit
  • Create an undo pool. This pool consists of the amount of undo space that can be consumed in by a group of users.
  • Configure an instance to use a particular method of allocating resources. You can dynamically change the method, for example, from a daytime setup to a nighttime setup, without having to shut down and restart the instance.

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