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.
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What is a log switch?
October 31st, 2009
What is log writer (LGWR)?
September 8th, 2009The 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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What is an online redo log group?
September 2nd, 2009An 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.
What is an undo segment?
September 2nd, 2009An 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.
What is Oracle’s password aging and expiration feature?
September 2nd, 2009Oracle’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.
What is Oracle’s password complexity verification feature?
September 2nd, 2009Oracle’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.
Download free practice test for Oracle OCP DBA 9i exam. Click here to get free 1Z0-031 Oracle9i Database: Fundamentals I exam practice questions.What is TO_CHAR (datetime) function?
September 1st, 2009TO_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.
What is high water mark?
July 29th, 2009The 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.
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What is a bitmap index?
July 26th, 2009A 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:
What is process monitor (PMON)?
July 25th, 2009The 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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