uCertify Articles » 1Z0-031 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 Download free practice test for Oracle OCA DBA 9i exam. -->

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.

Pass OCP DBA 9i in first attampt. Pass Oracle9i Database: Fundamentals I in first attampt. Share/Bookmark]]> http://www.ucertify.com/article/what-is-a-log-switch.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.

Share/Bookmark]]> http://www.ucertify.com/article/what-is-log-writer-lgwr-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.

Share/Bookmark]]> http://www.ucertify.com/article/what-is-an-online-redo-log-group-2.html/feed 0 What is an undo segment? http://www.ucertify.com/article/what-is-an-undo-segment-2.html http://www.ucertify.com/article/what-is-an-undo-segment-2.html#comments Wed, 02 Sep 2009 00:00:00 +0000 uCertify 1801131

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 Pass OCA DBA 9i in first attampt. -->

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.

Click here to download ocp-dba9i test study guide and practice question. Download practice question and study guide for 1Z0-031 for 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 Become Oracle OCA DBA 9i certified. -->

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.

Best exam simulation Oracle ocp-dba9i download free trial. 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 TO_CHAR (datetime) function? http://www.ucertify.com/article/what-is-to_char-datetime-function-2.html http://www.ucertify.com/article/what-is-to_char-datetime-function-2.html#comments Tue, 01 Sep 2009 00:00:00 +0000 uCertify 1801075

TO_CHAR (datetime) is a single-row function that is used to convert a value of DATE, TIMESTAMP, TIMESTAMP WITH TIME ZONE, or TIMESTAMP WITH LOCAL TIME ZONE datatype to a value of VARCHAR2 datatype in the specified date format.

Syntax:

TO_CHAR ( datetime [, fmt [, 'nlsparam' ]] )

where,

  • datetime specifies a value of DATE, TIMESTAMP, TIMESTAMP WITH TIME ZONE, or TIMESTAMP WITH LOCAL TIME ZONE datatype.

  • fmt specifies the date format in which the converted value is to be displayed.

  • nlsparam specifies the language in which the names and abbreviations of months and days are to be displayed.
    • Share/Bookmark]]>     http://www.ucertify.com/article/what-is-to_char-datetime-function-2.html/feed 0     What is high water mark? http://www.ucertify.com/article/what-is-high-water-mark.html http://www.ucertify.com/article/what-is-high-water-mark.html#comments Wed, 29 Jul 2009 00:00:00 +0000 uCertify 2201100

    The high water mark acts as an indicator within a data segment, which demarcates the used and the unused space, or space that has been formatted for user data. The space below this mark cannot be released even if there is no user data in it. If the segment is completely empty, a user can release that space by issuing the TRUNCATE .. DROP STORAGE statement.

    Share/Bookmark]]>     http://www.ucertify.com/article/what-is-high-water-mark.html/feed 0     What is a bitmap index? http://www.ucertify.com/article/what-is-a-bitmap-index.html http://www.ucertify.com/article/what-is-a-bitmap-index.html#comments Sun, 26 Jul 2009 00:00:00 +0000 uCertify 2201027

    A bitmap index is used for data warehouse applications, where there are large amounts of data. Queries are more frequently issued than data updates. Hence, bitmap index proves more efficient than conventional indexes in retrieving data. A bitmap index is built on columns with low cardinality, unlike the B-tree index that is built on columns with high cardinality. The bitmap index uses a bitmap to indicate that a row with the required key value exists. It does so by setting the bit at the corresponding column of the bitmap to 1. For example, consider that the bitmap index is built on a column that contains three distinct city names, Las Vegas, New York, and Paris. A conventional index employing the row-id value would look such as the one below:

    City Row-id
    New York SS1025AA
    Las Vegas SS1025AB
    New York SS1025AC
    Paris SS1025AD
    New York SS1025AE

    But, a bitmap index would be such as:

    City Bitmap
    New York 10101
    Las Vegas 01000
    Paris 00010

    The bitmap uses less storage space than conventional indexes such as the B-Tree index. It is also faster than other indexes because it uses binary mapping of rows, for which the retrieval time is comparatively low.

    Share/Bookmark]]>     http://www.ucertify.com/article/what-is-a-bitmap-index.html/feed 0     What is process monitor (PMON)? http://www.ucertify.com/article/what-is-process-monitor-pmon.html http://www.ucertify.com/article/what-is-process-monitor-pmon.html#comments Sat, 25 Jul 2009 00:00:00 +0000 uCertify 2201005

    The process monitor (PMON) is an Oracle background process that is responsible for performing the cleaning of failed user database connections. This process involves the releasing of blocks that were involved in the failed connection, from the database buffer cache. It also involves the releasing of the resources used by a user process at the time of connection failure. The resource releasing includes removing the locks from database objects that were involved in the failed connection, and removing process id’s of the failed processes from the list of active processes.

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