A resource consumer group is a logical grouping of user sessions on the basis of the resource requirements of each user session. Hence, there can be more than one resource consumer group with each having different resource requirements. Every user session can only belong to a single resource consumer group at an instance. At times, the resource requirement of a session is not met by the resource consumer group to which it belongs. In such cases, the session can automatically switch to a different resource consumer group depending on administrator settings.

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Locking is a mechanism implemented either on an entire table or a row. Locking avoids the destruction done by the transactions accessing the same resource. The resource may be data in a table or rows in a data dictionary.

In order to obtain the locks on resources, Oracle maintains the first in, first out (FIFO) serialized locking technique. Oracle uses a data structure known as ENQUEUE. For example, if there are various transactions trying to access the same resource simultaneously, then the very first transaction will acquire the lock. The rest of the transactions will be put in ENQUEUE waiting for the first transaction to complete.

The NLS_TIMESTAMP_TZ_FORMAT parameter is used to define the default timestamp with time zone format to use with the TO_CHAR and TO_TIMESTAMP_TZ functions.

Note: The value of the parameter is placed within single quotation marks as given below:

NLS_TIMESTAMP_TZ_FORMAT = ‘YYYY-MM-DD HH:MI:SS.FF TZH:TZM’

Some of the properties of the parameters are as follows:

• Parameter Type: String
• Syntax: NLS_TIMESTAMP_TZ_FORMAT = ‘format’
• Default value: the value is derived from NLS_TERRITORY
• Range of values: any valid datetime format mask

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Retrieving data using the SQL SELECT statement and using single row functions to customize the output

• /*…*/ and — are used to put comments in an Oracle program.
• The CREATE TABLE does not end immediately with a semicolon, and a column name cannot start with a numeric value. However, a numeric value can be used in between a column name.
• Name of a table cannot start with @ special character.
• Knowing about the GROUP BY clause.

Using sub queries and set operators to solve queries, as well as DDL statements to create and manage tables

• + (unary), – (unary), *, /, ||, =, !=, <, >, <=, >=, IS NULL, LIKE, BETWEEN, IN, NOT, AND, OR is the correct order of operators precedence.
• The ROLLBACK command is used to end the current transaction, and discard any changes made since the beginning of the transaction.

Managing objects with data dictionary views, schema objects and data in different time zones

• The length of a column can be increased even if it contains data. However, the data type of the column cannot be modified if it contains any data.
• The parameters used to maximize the space in Flash Recovery Area.
• User error failure refers to a database failure that results due to certain transactions on a database by a user.
• Flashback Query is used to view and repair historical data, and to view the contents of a table at any specific point in time.
• UNDO_RETENTION is a parameter in the init.ora initialization parameters file that specifies the time period in seconds for which a system retains undo data for committed transactions.
• Once the Flashback Versions Query is run to diagnose the erroneous transaction, the Flashback Transaction Query helps in the repair process of the transaction.
• The correct order of steps that will enable the flashback database are as follows:
  1. Put the database in Archive log mode.
  2. Set up a flash recovery area.
  3. Set the period for the flashback retention target.
  4. Shut down and mount the database.
  5. Enable flashback logging.
  6. Open the database.
• The overall utilization of the flash recovery area is displayed in megabytes.
• SQL statement can be used to flashback a database.
• Take the following steps to enable the Flashback Database:
  1. Ensure that the database is in Archive Log mode.
  2. Setup a flash recovery area.
  3. Set the duration for the flashback retention target.
  4. Shutdown the database.
  5. Mount the database.
  6. Enable flashback logging.
  7. Open the database.
• The dropped table can be recovered by using Flashback Drop.
• The flashback database is enabled only in Archive log mode, as it recovers the database to an earlier specific point of time.
• Flashback Database is used to reverse the changes made to a table.
• The Perform Recovery: Review screen is used to display the RMAN script that performs the Flashback Database recovery.
• The portlist.ini file is used to get all the port numbers of the HTTP listeners.
• RVWR is a background process, which is a part of the Flashback Database Architecture.
• LGWR is a background process that is a part of Flashback Database Architecture.
• SELECT oldest_flashback_scn FROM V; is used to retrieve an approximate system change number (SCN) to which a database can be flashed back.

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DBVERIFY is an Oracle external command-line utility that performs a physical data structure integrity check. This utility is used on backup files, online databases, and offline databases. The utility is executed by issuing the DBV command at the command prompt.

DBVERIFY is primarily used when it is to be ensured that a backup database (or datafile) is valid before being restored. It is also used as a diagnostic aid when data corruption problems are encountered. The integrity checks are extensively faster because DBVERIFY can be run against an offline database. This utility does not work against control files and redo logs as a matter of fact that DBVERIFY checks are limited to cache-managed blocks (that is, data blocks).

Following are the two command-line interfaces to DBVERIFY:

• With the first interface, the disk blocks of a single datafile can be specified for checking.
• With the second interface, a segment can be specified for checking.

This utility includes nine parameters, which are as follows:

1. FILE
2. START
3. END
4. BLOCKSIZE
5. LOGFILE
6. FEEDBACK
7. PARAFILE
8. USERID
9. SEGMENT_ID

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Enterprises are preferably switching from old existing Oracle versions, such as Oracle 8i and Oracle 9i, to Oracle 10g to have various additional profitable features. They often employ the Automatic Storage Management (ASM) option to enhance the manageability and consolidation of a database.

Oracle 10g

Oracle 10g is a revolutionary product in Oracle’s grid computing world. Oracle 10g is a DBMS, which can automate many database tasks. Oracle 10g follows the Oracle’s 9i platform; the letter ‘g’ in Oracle 10g signifies grid computing.

Oracle 10g delivers numerous interesting and dynamic new features. In this article, Automatic Storage Management (ASM) is explained in detail. There are many features available in Oracle 10g that help manage database operations more efficiently. One of the pivotal features of Oracle 10g is Automatic Storage Management (ASM). It is one of the storage options available in Oracle 10g.

Basic Functions of ASM

ASM relieves the burden of disk and storage management by defining the disk groups for file management, as a result of which file groups are reduced, and the time of the DBA is saved.

Note: The main function of ASM is to simplify and automate the database to manage Oracle database files. The RAC helps in automating the database management.

RAC

RAC stands for Real Application Cluster, which is a component provided by Oracle in its 9i version and which is now also available in the 10g version. RAC enables a database to be installed across multiple servers.

The image below depicts a window in which the configuration settings of Automatic Storage Management are detailed. A candidate has to enter the disk group name, the level of mirroring/redundancy, and the requisite data that the cursor therein prompts for. Click the Next button to proceed further.

This article will mainly focus on the following:

• ASM overview
• New features in ASM

ASM Overview

ASM is a very dynamic feature of Oracle 10g, which provides a grouped file system with no further investment on the software.

With ASM, there is no need of enhancing the storage resources for database management. ASM’s intelligent mirroring technology enables triple data protection. It is known as triple data protection because while configuring Automatic Storage Management, a user is provided three levels of redundancy, which are as follows:

• High
• Normal
• External

New Features in ASM

Following are the main new features of ASM:

1. ASM can support multiple database versions.
2. ASM enhances the manageability of the database.

ASM helps the DBA save money by optimizing storage utilization.

Oracle’s 10g version has enhanced the ASM functionality in the clustered environment, allowing one ASM instance per client to manage all database instances in the cluster, which has removed the requirement of maintaining more than one ASM instance to manage individual database instances.

For higher availability and manageability, ASM’s instance should be installed in a separate ORACLE_HOME parameter, which is ASM_HOME.

ASM enhances I/O performance, as the database files are intelligently distributed across the current active devices. While adding more resources, database file distribution is re-balanced, keeping the database up and running.

ASM has mirroring capability to enhance manageability, which means that ASM can keep duplicate copies of data as a backup for recovery purposes.

Note: DBAs should note that ASM is not general-purpose, and will not replace the OS file system because ASM’s file resources are not directly managed by the OS, but rather it is the ASM’s file resources, which are managed by the file management system of the OS.

Preparing hard disk for configuration of ASM

If the DBA is configuring ASM for Windows NT OS, then the following points should be taken into consideration:

• Investigate for enough space on the system’s hard disk.
• Using the disk partitioning utility (DISKPART.EXE) of Windows creates primary disk partitions, deciding the size of each partition.

Following example can give an idea about how to create partitions:

C:>Select disk1
C:Disk1 selected.
C:Create partition primary size = 100
C:Partition created.
C:Create partition primary size = 100
C:Partition created.
……………….

The following image depicts the list of volumes created via the DISKPART.EXE utility in a Windows NT environment.

This article helps in understanding the fundamental functionality of Automatic Storage Management (ASM).

The n-tier architecture is the most advanced type of architecture for a network configuration. This architecture introduces middleware components, such as application servers and Web servers between clients and the database server.

An example of the n-tier architecture is the Internet. The n-tier architecture is the most preferred architecture for an enterprise network. This architecture reduces processing load on the server.

An implicit lock is a lock that a row or a table acquires automatically, depending on the database operations such as ALTER TABLE, UPDATE, SELECT etc.

The REMOTE_OS_AUTHENT parameter in the parameter file of the database specifies whether remote clients will be authenticated with the value of the OS_AUTHENT_PREFIX parameter or not. The type of the REMOTE_OS_AUTHENT parameter is Boolean, the default value is false, and the parameter class is static. The REMOTE_OS_AUTHENT parameter is case sensitive on some operating systems. The flow diagram below may help a user understand the role of the REMOTE_OS_AUTHENT parameter for a remote database:

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A deadlock refers to a condition, in which, two or more processes simultaneously wait for each other to complete, as a result of which both, or all of them, as the case may be, hang. Deadlocks are generally encountered in multitasking, multiprocessing, and client-server environments.

Deadlocks are also known as deadly embraces and starvation deadlocks. The term deadly embrace is preferable in Europe, in which only two processes are responsible for a deadlock-like situation and the word deadlock predominates in the United States.