uCertify Articles » OCA DBA 9i http://www.ucertify.com/article Just another WordPress weblog Wed, 04 Nov 2009 00:00:00 +0000 http://wordpress.org/?v=2.8.4 en hourly 1 What is a log switch? http://www.ucertify.com/article/what-is-a-log-switch.html http://www.ucertify.com/article/what-is-a-log-switch.html#comments Sat, 31 Oct 2009 00:00:00 +0000 uCertify 1801112 Click here to download oca-dba9i test study guide and practice question. -->

A log switch occurs when the log writer (LGWR) finishes writing redo entries to the current online redo log file group and starts writing to the next online redo log file group. By default, a log switch occurs automatically when the current online redo log file group is full. A log switch can also be forced by executing the ALTER SYSTEM SWITCH LOGFILE; statement, regardless of whether or not the current online redo log file group is full.

Download practice question and study guide for ocp-dba9i for exam. Click here to download 1Z0-031 test study guide and practice question. Share/Bookmark]]> http://www.ucertify.com/article/what-is-a-log-switch.html/feed 0 OCP 1z0-047 Short Notes: Exam passing tips http://www.ucertify.com/article/ocp-1z0-047-short-notes-exam-passing-tips-2.html http://www.ucertify.com/article/ocp-1z0-047-short-notes-exam-passing-tips-2.html#comments Sat, 03 Oct 2009 00:00:00 +0000 uCertify 3701677

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.
Share/Bookmark]]> http://www.ucertify.com/article/ocp-1z0-047-short-notes-exam-passing-tips-2.html/feed 0 What is the REMOTE_OS_AUTHENT parameter? http://www.ucertify.com/article/what-is-the-remote_os_authent-parameter-2.html http://www.ucertify.com/article/what-is-the-remote_os_authent-parameter-2.html#comments Wed, 30 Sep 2009 00:00:00 +0000 uCertify 3701252

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:

Share/Bookmark]]> http://www.ucertify.com/article/what-is-the-remote_os_authent-parameter-2.html/feed 0 What is log writer (LGWR)? http://www.ucertify.com/article/what-is-log-writer-lgwr-2.html http://www.ucertify.com/article/what-is-log-writer-lgwr-2.html#comments Tue, 08 Sep 2009 00:00:00 +0000 uCertify 2201007

The log writer (LGWR) is an Oracle background process. It is responsible for writing all the new entries that have been copied in the redo log buffer since the LGWR last wrote the entries to a redo log file. The log writer should write the entries of the redo log buffer fast enough, so that buffers are immediately available for new entries.

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The DBMS_SESSION PL/SQL package is used to provide access to the ALTER SESSION and ALTER SYSTEM statements. This package is also used for gathering session related information. The DBMS_SESSION PL/SQL package uses the privileges of the user executing this package, instead of using privileges of the user SYS.

Share/Bookmark]]> http://www.ucertify.com/article/what-is-dbms_session-plsql-package-2.html/feed 0 What is an online redo log group? http://www.ucertify.com/article/what-is-an-online-redo-log-group-2.html http://www.ucertify.com/article/what-is-an-online-redo-log-group-2.html#comments Wed, 02 Sep 2009 00:00:00 +0000 uCertify 1801126

An online redo log group consists of an online redo log file that may or may not be multiplexed. In other words, an online redo log group may be a single online redo log file or a set of identical copies of an online redo log file. Each copy of an online redo log file in an online redo log group is called a member.

Log writer (LGWR) writes redo records to only one online redo log group at a time. However, it simultaneously writes the same information to all its members. A database must have at least two online redo log groups, as LGWR writes to them in a circular manner. All online redo log groups in an Oracle database are collectively known as online redo log.

The online redo log group that LGWR is currently writing to is called the current online redo log group. When the current online redo log group is full, LGWR starts writing to the next available online redo log group. Each time LGWR starts writing to an online redo log group, Oracle assigns a new log sequence number to the online redo log group. The current log sequence number of an online redo log group is stored in control files and headers of all data files.

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An undo segment holds all undo data of a database when the database is running in automatic undo management mode. An undo segment is internally similar to a rollback segment that is used to hold undo data of a database when the database is running in manual undo management mode.

When a transaction modifies data in a database, the before image of the modified data is stored in an undo segment. If the transaction is rolled back, Oracle restores the original values by writing the values stored in the undo segment back to the modified rows.

During an instance recovery, the values stored in an undo segment are used to roll back the uncommitted transactions. The values stored in an undo segment also provide the transaction-level or statement-level read consistency, i.e., database users are able to see a consistent image of data even if the data is being modified by another user at the same time.

Share/Bookmark]]> http://www.ucertify.com/article/what-is-an-undo-segment-2.html/feed 0 What is Oracle’s password aging and expiration feature? http://www.ucertify.com/article/what-is-oracles-password-aging-and-expiration-feature-2.html http://www.ucertify.com/article/what-is-oracles-password-aging-and-expiration-feature-2.html#comments Wed, 02 Sep 2009 00:00:00 +0000 uCertify 1801150 Become Oracle OCA DBA 9i certified. -->

Oracle’s password aging and expiration feature ensures that the password of a user account expires after a specified number of days. The user or the database administrator must change the password once it has expired. The PASSWORD_LIFE_TIME parameter is used to specify the number of days after which a user account’s password expires.

A grace period can also be specified for the password expiration. A grace period is the number of days for which a user can use his account, even after his account’s password has expired. During the grace period, a warning message appears each time the user logs in to the database. If the user does not change the password within the grace period, the password expires. Thereafter, he is prompted to change the password when he attempts to log in to the database. He cannot log in until he changes the password. The PASSWORD_GRACE_TIME parameter is used to specify the grace period.

Download free practice test for ocp-dba9i OCP DBA 9i exam. Download free practice test for Oracle Oracle9i Database: Fundamentals I exam. Share/Bookmark]]> http://www.ucertify.com/article/what-is-oracles-password-aging-and-expiration-feature-2.html/feed 0 What is Oracle’s password complexity verification feature? http://www.ucertify.com/article/what-is-oracles-password-complexity-verification-feature-2.html http://www.ucertify.com/article/what-is-oracles-password-complexity-verification-feature-2.html#comments Wed, 02 Sep 2009 00:00:00 +0000 uCertify 1801151 Get certified in first attempt download oca-dba9i - OCA DBA 9i simulation. -->

Oracle’s password complexity verification feature ensures that a password is too complex to be guessed easily. The complexity of a password can be verified before a user can set the password for his account. The PASSWORD_VERIFY_FUNCTION parameter specifies a PL/SQL script that is used to verify the complexity of a password. Oracle provides a default PL/SQL script for this purpose. However, users can also create their own scripts. For example, a script can be created to verify that a password has a minimum length of four characters, the password is not the same as the account’s name, the password has at least one alphabetical, one numeric, and one punctuation mark character, the password is not a simple or obvious word, and the password differs from the previous password by at least three characters.

Pass OCP DBA 9i in first attampt. Pass Oracle 1Z0-031 - Oracle9i Database: Fundamentals I Share/Bookmark]]> http://www.ucertify.com/article/what-is-oracles-password-complexity-verification-feature-2.html/feed 0 What is DECODE function? http://www.ucertify.com/article/what-is-decode-function-2.html http://www.ucertify.com/article/what-is-decode-function-2.html#comments Tue, 01 Sep 2009 00:00:00 +0000 uCertify 1801007

The DECODE function decodes a column value or an expression and compares it with each specified search value, one by one. If the expression matches a search value, a result value corresponding to the matching search value is returned. If no match is found, a default result value, if included, is returned. However, if no default value is included, a NULL value is returned. The DECODE function is one of the few single-row functions that directly deal with NULL values. It can compare two NULL values and can return a NULL value.

Syntax:

DECODE (ColumnExpression, search, result[, search, result, ...] [, default] )

ColumnExpression, search, and result can be of the CHAR, VARCHAR2, NCHAR, or NVARCHAR2 datatype.

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