uCertify Articles » 1Z0-032 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 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 How are the archived redo log files’ names determined when automatic archiving is enabled? http://www.ucertify.com/article/how-are-the-archived-redo-log-files-names-determined-when-automatic-archiving-is-enabled-2.html http://www.ucertify.com/article/how-are-the-archived-redo-log-files-names-determined-when-automatic-archiving-is-enabled-2.html#comments Fri, 04 Sep 2009 00:00:00 +0000 uCertify 1801237

When a database is running in ARCHIVELOG mode, and automatic archiving is enabled, the archiver process (ARCn) automatically archives the filled online redo log files at specified archive destinations. ARCn automatically decides the names of the archived redo log files by looking at the LOG_ARCHIVE_FORMAT parameter in the initialization parameter file. The LOG_ARCHIVE_FORMAT initialization parameter specifies a default filename format for the archived redo log files. It uses a text string and certain variables to specify the default filename format. This helps Oracle keep the archived redo log files’ names sequential, unique, and easily identifiable from other files.

The following variables can be used in the filename format:

  • %s: It specifies the current log sequence number.

  • %t: It specifies the thread number.

    • Example:

    LOG_ARCHIVE_FORMAT = “Log%s_%t.arc”

    If the current log sequence number is 5, and the thread number is 1, the corresponding archived redo log file’s name will be Log5_1.arc (according to the Log%s_%t.arc filename format).

    Using the uppercase letters for the above variables (e.g., %S and %T) causes the value to be of a fixed length and padded to the left with zeros.

    Become Oracle OCP DBA 9i certified. Get certified in first attempt download 1Z0-032 - Oracle9i Database: Fundamentals II simulation. Share/Bookmark]]>     http://www.ucertify.com/article/how-are-the-archived-redo-log-files-names-determined-when-automatic-archiving-is-enabled-2.html/feed 0     What is a connect identifier? http://www.ucertify.com/article/what-is-a-connect-identifier-2.html http://www.ucertify.com/article/what-is-a-connect-identifier-2.html#comments Fri, 04 Sep 2009 00:00:00 +0000 uCertify 1801247

    A connect identifier is either a connect descriptor or a name that resolves to a connect descriptor. One of the most common connect identifiers is a net service name (a simple name for a database service). A database service name, alias, or net service alias can also be specified as a connect identifier. Users initiate a connection request to a database service by providing a connect string with the CONNECT command on the command line. A connect string includes a username and password, along with a connect identifier.

    Syntax:

    CONNECT username/password@ connect_identifier

    For example, out of the following two connect strings, the first connect string uses a connect descriptor as the connect identifier and the second string uses a net service name sales as the connect identifier:

    1. CONNECT scott/tiger@ (DESCRIPTION= (ADDRESS= (PROTOCOL=tcp) (HOST=sales-server1) (PORT=1521)) (CONNECT_DATA= (SERVICE_NAME=sales.us.acme.com)))
    2. CONNECT scott/tiger@ sales
    Pass Oracle ocp-dba9i - OCP DBA 9i Download practice question and study guide for 1Z0-032 for exam. Share/Bookmark]]>     http://www.ucertify.com/article/what-is-a-connect-identifier-2.html/feed 0     What is service registration? http://www.ucertify.com/article/what-is-service-registration-2.html http://www.ucertify.com/article/what-is-service-registration-2.html#comments Thu, 03 Sep 2009 00:00:00 +0000 uCertify 1801172

    A listener is configured with one or more listening protocol addresses, information about supported services, and listener parameters that control the listener’s run-time behavior. The listener configuration is stored in a configuration file named listener.ora. The supported services (the services to which the listener forwards client requests) can be configured in the listener.ora file or can be dynamically registered with the listener. The dynamic registration feature is called service registration. The service registration is performed by the PMON (Process Monitor) background process of each instance of the database, which has the necessary configuration in the database’s initialization parameter file.

    Service registration provides the following information to the listener:

  • Service names for each running instance of the database

  • Names of instances of the database

  • Service handlers (dispatcher or dedicated server) available for each instance of the database

  • Load information about dispatcher, instance, and node (load information enables the listener to forward client connection requests to the least loaded instance and dispatcher or dedicated server)

    • Since this information is dynamically registered with the listener, this information does not need to be stored in the listener.ora file (i.e., listener.ora file does not need to be statically configured with this information). However, the static configuration is required if the listener is to accept client connection requests for pre-Oracle8i databases. Static configuration is also required for other services, such as external procedures, heterogeneous services, and some management tools such as Oracle Enterprise Manager. For Oracle8i and Oracle9i databases, the listener uses dynamic service information received through service registration before using statically configured information in the listener.ora file.

    Download practice question and study guide for ocp-dba9i for exam. Click here to download 1Z0-032 test study guide and practice question. Share/Bookmark]]>     http://www.ucertify.com/article/what-is-service-registration-2.html/feed 0     What is a media failure? http://www.ucertify.com/article/what-is-a-media-failure-2.html http://www.ucertify.com/article/what-is-a-media-failure-2.html#comments Thu, 03 Sep 2009 00:00:00 +0000 uCertify 1801200

    A media failure occurs when a physical problem prevents Oracle from writing or reading a database file that is required for continuing the database operation. For example, when a disk head crashes, all the database files on the disk drive are lost. Disk failure can affect a variety of files, including the data files, redo log files, and control files. Because the database instance cannot continue to function properly, it cannot write the data from the database buffer cache of the system global area (SGA) to the data files.

    The appropriate recovery from a media failure depends on the files affected. Media failure is the primary concern of a backup and recovery strategy because it typically requires restoring some or all the database files and the application of redo data during the recovery.

    Share/Bookmark]]>     http://www.ucertify.com/article/what-is-a-media-failure-2.html/feed 0     How is an Oracle shared server configured? http://www.ucertify.com/article/how-is-an-oracle-shared-server-configured-3.html http://www.ucertify.com/article/how-is-an-oracle-shared-server-configured-3.html#comments Thu, 03 Sep 2009 00:00:00 +0000 uCertify 1801223

    To configure an Oracle shared server, the following processes must be set to run on the server:

  • Listener process: A listener process contains the addresses of all the dispatchers in the Oracle shared server. The job of a listener is to constantly look out for user requests. Whenever it finds a user request, it returns the address of the least heavily loaded dispatcher to which the user process can connect. A listener process is configured by using a centralized listener configuration file called listener.ora.
  • Dispatcher process: At least one dispatcher process must be running on an Oracle server in order to make it behave as an Oracle shared server. However, there must be a minimum of one dispatcher process configured for each network protocol used for a connection with the Oracle shared server. The job of a dispatcher process is to send user requests to a pool of Oracle server processes. After an Oracle server process has executed a request, the process sends the result back to the dispatcher that had sent the request. Consequently, the dispatcher sends the result to the user process.

    Configuring the DISPATCHERS initialization parameter in the initialization parameter file starts the preset number of dispatcher processes when an Oracle instance is started. The maximum number of dispatchers process that can be started is determined by the MAX_DISPATCHERS initialization parameter.

  • Shared server process: At least one shared server process must be running on an Oracle server in order to make it behave as an Oracle shared server. In an Oracle shared server configuration, Oracle starts a fixed number of shared server processes when an Oracle instance starts. These server processes work in a round-robin fashion to serve requests from multiple user processes. Shared server processes terminate when the associated Oracle instance is terminated.

    The number of shared server processes to be started at the instance startup is determined by the SHARED_SERVERS initialization parameter. The maximum number of shared server processes that can be started is determined by the MAX_SHARED_SERVERS initialization parameter.

    • Note: In order to configure an Oracle shared server, Oracle requires Oracle Net Services or SQL*Net version 2. Also, to use an Oracle shared server, a user process must connect through Oracle Net Services or SQL*Net version 2, even if the user process and the shared server process are running on the same computer.

    Click here to get free ocp-dba9i OCP DBA 9i exam practice questions. Get certified in first attempt download 1Z0-032 - Oracle9i Database: Fundamentals II simulation. Share/Bookmark]]>     http://www.ucertify.com/article/how-is-an-oracle-shared-server-configured-3.html/feed 0     What is a statement failure? http://www.ucertify.com/article/what-is-a-statement-failure-2.html http://www.ucertify.com/article/what-is-a-statement-failure-2.html#comments Thu, 03 Sep 2009 00:00:00 +0000 uCertify 1801233

    A statement failure occurs when there is a logical failure in the handling of a statement in an Oracle program. For example, when all extents of a table (in other words, the number of extents specified in the MAXEXTENTS parameter of the CREATE TABLE statement) are allocated and completely filled with data, a valid INSERT statement cannot insert a row because no space is available. Therefore, the statement fails.

    If a statement failure occurs, the Oracle software or operating system returns an error. A statement failure does not require any recovery step. Oracle automatically resolves the statement failure by rolling back the effects of the statement and returning control to the application. The user can execute the statement again after the problem indicated by the error message is corrected. For example, if insufficient extents are allocated, the database administrator (DBA) needs to allocate more extents so that the user’s statement can be executed.

    Share/Bookmark]]>     http://www.ucertify.com/article/what-is-a-statement-failure-2.html/feed 0     How are archive destinations specified? http://www.ucertify.com/article/how-are-archive-destinations-specified-2.html http://www.ucertify.com/article/how-are-archive-destinations-specified-2.html#comments Thu, 03 Sep 2009 00:00:00 +0000 uCertify 1801236

    When archiving redo logs, it must be decided whether to archive them to a single archive destination or multiplex them. When the archived redo logs are multiplexed, they are archived to more than one archive destination. The following two methods can be used to specify archive destinations:

    1. Using the LOG_ARCHIVE_DEST_n initialization parameter: The LOG_ARCHIVE_DEST_n (where n is an integer from 1 to 10) initialization parameter can be used to specify a maximum of ten different local or remote archive destinations. Each numerically suffixed parameter (e.g., LOG_ARCHIVE_DEST_1, LOG_ARCHIVE_DEST_2, etc.) uniquely identifies an individual destination.

      For specifying a local archive destination, the LOCATION keyword is used with the LOG_ARCHIVE_DEST_n initialization parameter.

      Example:

      LOG_ARCHIVE_DEST_1 = ‘LOCATION = /Disk1/Archive’
      LOG_ARCHIVE_DEST_2 = ‘LOCATION = /Disk2/Archive’

      The LOCATION keyword specifies an operating system-specific path name.

      For specifying a remote archive destination (e.g., a remote standby database), the SERVICE keyword is used with the LOG_ARCHIVE_DEST_n initialization parameter.

      Example:

      LOG_ARCHIVE_DEST_4 = ‘SERVICE = Standby_Dbase1′

      The SERVICE keyword specifies a valid net service name or alias. Oracle resolves the net service name to a connect descriptor by using a tnsnames.ora file. The connect descriptor contains the information necessary for connecting to the remote standby database. The net service name must have an associated database system identifier (SID), so that Oracle correctly updates the log history of the control file for the remote standby database.

      The destinations specified by the LOG_ARCHIVE_DEST_n initialization parameter can be established as mandatory or optional by using the MANDATORY or OPTIONAL keyword respectively with the LOG_ARCHIVE_DEST_n initialization parameter. If no keyword is specified, it is taken as OPTIONAL. The archiver process (ARCn) must successfully archive a redo log to a mandatory archive destination before the redo log can be reused.

    2. Using the LOG_ARCHIVE_DEST and LOG_ARCHIVE_DUPLEX_DEST initialization parameters: This method allows specifying a maximum of two archive destinations. The LOG_ARCHIVE_DEST initialization parameter is used to specify a primary local archive destination, and the LOG_ARCHIVE_DUPLEX_DEST initialization parameter is used to specify an optional secondary local archive destination. These parameters cannot be used to specify a remote archive destination. Whenever Oracle archives a redo log, it archives it to both destinations.

      Example:

      LOG_ARCHIVE_DEST = ‘/Disk1/Archive’
      LOG_ARCHIVE_DUPLEX_DEST = ‘/Disk2/Archive’

      3. Any archive destination declared by the LOG_ARCHIVE_DEST initialization parameter is mandatory. However, any archive destination declared by the LOG_ARCHIVE_DUPLEX_DEST initialization parameter is optional if LOG_ARCHIVE_MIN_SUCCEED_DEST = 1, and mandatory if LOG_ARCHIVE_MIN_SUCCEED_DEST = 2. Where, LOG_ARCHIVE_MIN_SUCCEED_DEST is an optional initialization parameter that determines the minimum number of archive destinations to which the archiver process (ARCn) must successfully archive a redo log before the redo log can be reused.

    While archiving, Oracle automatically names the archived redo log files according to the file name format specified by the LOG_ARCHIVE_FORMAT initialization parameter.

    Share/Bookmark]]>     http://www.ucertify.com/article/how-are-archive-destinations-specified-2.html/feed 0     What is a listener.ora file? http://www.ucertify.com/article/what-is-a-listenerora-file-2.html http://www.ucertify.com/article/what-is-a-listenerora-file-2.html#comments Wed, 02 Sep 2009 00:00:00 +0000 uCertify 1801170

    A listener.ora file is a listener configuration file that is used to configure listeners on an Oracle server. Only one listener.ora file can be configured for an Oracle server. However, a single listener.ora file contains configuration information for all the listeners configured on the Oracle server. A listener.ora file identifies the following information for a listener:

    • Listener’s name

    • Protocol addresses on which the listener is accepting connection requests

    • Services for which the listener is listening

    The listener.ora file typically resides in /network/admin on UNIX platforms and ORACLE_HOME
    etworkadmin on Windows NT.

    Share/Bookmark]]>     http://www.ucertify.com/article/what-is-a-listenerora-file-2.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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