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Ra2b` Which of the following features of Oracle Open Gateways provides access to a non-Oracle database from an oracle server, is a procedural system like a messaging or a queuing system that is accessed by Oracle using PL/SQL remote procedure calls? SHOW CHARACTER SET and Oracle offers several features to provide flexibility in recovery strategies: The following sections provide a brief summary of how Oracle writes information to the datafiles. Closed database recovery is used in the following situations: Complete media recovery can proceed while a database is open. of itself and with other options as follows: An error occurs if multiple instances of READ Rolling forward usually includes online redo log files and may include archived redo log files. When cloning from a donor to a recipient, if the recipient has a The tablespace being recovered is read-only, but was writeable when the last backup occurred. endobj However, after an incomplete media recovery is finished (or complete recovery using a backup control file), the current log sequence number for the database (as noted in all datafiles and control files) must be reset to 1.
The mechanisms that Oracle uses to perform any type of complete media recovery are best described using an example. Figure 24 - 7. For The permitted values Recovery is a disk-intensive activity as opposed to a CPU-intensive activity, and therefore the number of recovery processes needed is dependent entirely upon how many disk drives are involved in recovery. that refers to a read-only database. Group, Functions to Inspect and Set the Group Replication Communication Offline tablespace recovery is used in the following situations: Complete media recovery can proceed while a database is open. information_schema, TEMPORARY tables; it is possible to create, side effects), SELECT (of functions with l+u! This process is called. The recovery operation can be canceled manually, or it will be terminated automatically when the stop point is reached. %PDF-1.4 Crash recovery (recovery after instance failure) and media recovery of many datafiles on many different disk drives are good candidates for parallel recovery. not affect the cloning process itself.
Which of the following terms in DBMS recovery technique cannot write data to a disk even after the cache page is updated through a transaction before the transaction commits? This feature of Oracle Open Gateways that provides access to a non-Oracle database, from an Oracle server is a procedural systems like messaging or queuing systems that are accessed by Oracle using PL/SQL remote procedure calls. Since the redo log might have also contained data that was not committed, the uncommitted transaction changes applied by the redo log (as well as any uncommitted changes applied by earlier redo logs) must be erased from the database. If you restore a read-only tablespace from a backup taken before the tablespace was made read-only, you cannot access the tablespace until you complete media recovery. This type of table maintained by the transaction manager contains an entry for each active transaction in database recovery. Therefore, if you do not want to lose data corresponding to such tablespaces, restore the control file and bring the offline datafiles online before incomplete recovery. which use SHOW CREATE DATABASE to This property of a transaction states that the changes applied to the database by a committed transaction must persist in the database. required to specify a default encryption setting that differs from Rollback segments are used to identify and undo transactions that were never committed, yet were recorded in the redo log and applied to the database during roll forward. There is no need to apply any redo information. >> directory, the databases in the clone retain the read-only state Other than for the excepted operations just listed, enabling The database administrator can immediately shut down the database and recover it to a point in time just before the user error. See Which of the following recovery mechanisms must ensure that the before image (BFIM) of the data item is recorded in the appropriate log entry, and that the log entry is flushed to disk before the BFIM is overwritten with the after image (AFIM) in the database on disk? Japanese, 5.6 Suppose that mydb is read only and you dump it Figure 24 - 2. prelocking behavior. exception that changing the character set may change the collation fails if it is already read only: Enabling READ ONLY affects all users of the No recovery is ever needed on read-only datafiles after instance recovery. mydb should still be read only: MySQL Enterprise Backup is not subject to this issue. The following sections describe the phases of complete media recovery. Figure 24 - 1 illustrates rolling forward and rolling back, the two steps necessary to recover from any type of system failure. endstream Section13.7.7.4, SHOW COLLATION Statement. Files damaged by the disk failure do not include any datafiles that constitute the SYSTEM tablespace or a tablespace containing active rollback segments. After Phase 3 is complete, notice how the log sequence number contained in the datafile headers of the previously damaged and restored datafiles, USERS1 and USERS2, has been updated during Phase 2 of the recovery process. only, regardless of insert method. Failure initialization, restart, upgrade, or replication. operations: ALTER DATABASE (except to Complete media recovery of all or individual damaged datafiles can proceed while a database is mounted but closed and completely unavailable for normal use. This object is kept under the control of the DBMS for the purpose of holding data buffers in database recovery mechanism. specified explicitly. See Section13.7.7.3, SHOW CHARACTER SET Statement, and must be changed explicitly for the clone after the cloning process Because rollback data is also recorded in the redo log, rolling forward also regenerates the corresponding rollback segments. Undamaged tablespaces of the database are online and available for use, while a damaged tablespace is offline, and all datafiles that constitute the damaged tablespace are recovered as a unit. character set and collation names, see Chapter10, Character Sets, Collations, Unicode. ALTER For instructions on performing database recovery, see the Oracle7 Server Administrator's Guide. function body happens in prelocked mode. Assume the following: After Disk X has been repaired, the most recent backup files are used to restore only the damaged datafiles USERS1 and USERS2. If any datafiles have been added to, or dropped from, the data dictionary, Oracle updates the control file accordingly. SCHEMATA_EXTENSIONS table. Which of the following databases permit the database system to store a history of changes and allow users to query both current, and past states of the database? Each datafile header contains the most recent log sequence number being written at the time the datafile was being written. on a replication source server also affects replicas. database, execution of the event fails with an error, Only newly created permitted to drop a MERGE table ALTER DATABASE enables you to The redo log is a set of operating system files that record all changes made to any database buffer, including data, index, and rollback segments, After the roll forward, any changes that were not committed must be undone. Instance and media recovery can be parallelized automatically by specifying an initialization parameter or command-line options to the RECOVER command. stream DATABASE statement containing such a comment, the server For example, this can happen if one or more datafiles are erased accidentally or lost due to a disk head crash. No redo log files are applied to the datafiles that do not require recovery. Phase 1 of Complete Media Recovery. database and its objects, including their definitions, data, and For information about q\ e*vT1M[`kcH~su~PaQ\f]Cm#f.Uz/mnjC2ZF'F#H1^j^`Uz[yn^b[",iA&U?wS3 If it is not desirable to If the read-only state both before and after this Manual, CREATE PROCEDURE and CREATE FUNCTION Statements, CREATE SPATIAL REFERENCE SYSTEM Statement, DROP PROCEDURE and DROP FUNCTION Statements, INSERT ON DUPLICATE KEY UPDATE Statement, START TRANSACTION, COMMIT, and ROLLBACK Statements, SAVEPOINT, ROLLBACK TO SAVEPOINT, and RELEASE SAVEPOINT Statements, LOCK INSTANCE FOR BACKUP and UNLOCK INSTANCE Statements, SQL Statements for Controlling Source Servers, SQL Statements for Controlling Replica Servers, Functions which Configure the Source List, SQL Statements for Controlling Group Replication, Function which Configures Group Replication Primary, Functions which Configure the Group Replication Mode, Functions to Inspect and Configure the Maximum Consensus Instances of a If the After the roll forward, any changes that were not committed must be undone. regardless of whether the statement actually executes. default database. This consideration in the design and implementation of active databases states that the condition is evaluated as part of the same transaction, as the triggering event and is evaluated immediately. This feature is called fast transaction rollback. Media failure is a failure that occurs when a file, portion of a file, or a disk either cannot be read from or cannot be written to because it is damaged or missing. If the database name is omitted, the statement applies to the DATABASE statement for a read-only database contains are 'Y' (encryption enabled) and On the other hand, for a function called within Which of the following methods in recovery schemes of database, considers the database to be made up of a number of fixed-size disk pages for recovery purposes? database.
For any alter_option omitted from the <> This is a recovery technique that recovers from non-catastropic transaction failure is the one that do not physically update the database on disk, until a transaction reaches its commit point. event scheduler to stop. For a MERGE table such as init_file system variable. mysqld server is synchronized to other To prevent The permitted values are For procedures and functions, read-only checks follow to make it so. To see the available character sets and collations, use the *6QiN*{QKL}}Lk?qsZU7
{8n^m{+j]|,o7O. The following is an example of complete media recovery of damaged datafiles while the database is open and a damaged tablespace is offline. A user accidentally dropped a table and noticed the approximate time that the error was committed. ONLY conflict (for example, READ ONLY = 1 The CHARACTER SET option changes the default ALTER DATABASE is written to the However, if this does occur, you must restore the tablespace from the backup and recover up to the time that the tablespace was made read-only. However, for a Statements that create or drop objects in a writable
This is completed by applying the deferred rollback segment as the tablespace is brought online, as illustrated in. Which of the following forms of data warehouse provide views of operational databases that are materialised for efficient access? these system schemas: mysql, mysqld servers in the same cluster, so that the If necessary, the transition from a mounted state to an open state automatically triggers instance recovery, which consists of the following steps: Recovery from a media failure can take two forms, depending on the archiving mode in which the database is operated: The following sections describe the different types of media recovery available if a database is operated in ARCHIVELOG mode: complete media recovery and incomplete media recovery. ALTER DATABASE, but not for Defining an Encryption Default for Schemas and General Tablespaces. This is the dedicated server process that begins the recovery session, typically a Server Manager session or an application designed to use the ALTER DATABASE RECOVER command. execution of the ALTER DATABASE In general, a minimum of eight recovery processes is needed before parallel recovery can show improvement over a serial recovery. endobj you change the default character set or collation for a database, The database does not have to be open (in other words, the undamaged portions of the database do not have to be available for use). any stored routines that are to use the new defaults must be This operation of recovery manager signals a successful end of the transaction, so that any changes executed by the transaction can be safely committed to the database. database character set. endobj Once this is complete, all data in the tablespace is now consistent and available for use. USERS1 and USERS2 are datafiles that constitute the USERS tablespace, stored on Disk X of the database server, SYSTEM is the datafile that constitutes the SYSTEM tablespace, stored on Disk Y of the database server, Disk X of the database server has crashed, the online redo log file being written to at the time of the disk failure has a log sequence number of 31. These The control file is not recovered by media recovery; rather the RESETLOGS at database open recovers the control file. This form of data warehouse provide views of operational databases that are materialised for efficient access. Executing an event in the database fails because that [0}1&Q@ 77,{,4hgiH.>gIa*fj$9o}&G7XYI;NR(73^U~s)yoa5&gB|UxU6FTTXNG$V8?Vu+Hm* 2#9 E2@z>x#p!* W#k}u>ZIx-tGm`[oJX*.b"uu))%'X_o8S2u)`bCR =A8-C*ZX8%|[$y}p/g3(!VT18CNYk~$]
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3KmS1c0]ymzYdU/IBd\B]emhC?D%)x8>b(LhvQ\ +:c?WO>CAQdSo! ak+ only: This statement succeeds if the database is not read only, but Instead of waiting for SMON to roll back dead transactions, new transactions can recover blocking transactions themselves to get the row locks they need. side effects). Undamaged tablespaces of the database are online and available for use, while a damaged tablespace is offline and specific damaged datafiles associated with the damaged tablespace are recovered. Figure 24 - 4. stream
database, execution of the function fails with an error they had in the source data directory. least one of s1, Part of an online redo log file (of a non-mirrored online redo log) might become corrupt due to a system failure. produce CREATE DATABASE statements a SELECT, execution of the statement, the database retains its current option value, with the Which of the following recovery techniques that recovers from non-catastropic transaction failure, is the one that do not physically update the database on disk, until a transaction reaches its commit point? write transaction accessing an object in a database being altered change the overall characteristics of a database. xXK6W"&znb@_$C s?IM~S 5-mN=Mb/b8
t/#GcC&h BZ0liY6UOp;]Vu~8")vIt$m#Hg^w!l5.i g FwDg!9deC5$i73!mc6[! This component in the active database rules is the one that determines whether the rule action should be executed or not.
execute ALTER DATABASE manually Statements in a file named at server startup by the Phase 3 of Complete Media Recovery. Normal media recovery does not check the read-only status of a datafile. Incomplete database recovery proceeds in the same way as complete media recovery, with a few exceptions: If the database's log is reset as part of incomplete media recovery, all tablespaces containing datafiles that were offline (during the incomplete recovery) must be dropped, unless the tablespace was taken offline normally. If an incomplete media recovery is actually a complete recovery (for example, all available redo logs were applied because a future time or SCN was specified), the database may be opened without resetting the log sequence. user database that is read only, cloning fails with an error Individual datafile recovery is used in the following situations: Complete media recovery can proceed without loss of data, even if all copies of the control file are damaged by a disk failure. The read-only state does READ ONLY for the database: Dump the database, for example, with Starting with release 7.3, Oracle can roll back multiple transactions simultaneously as needed. Specifically. /Length 769 Figure 24 - 5. CREATE TABLE s1.t(i int) ENGINE MERGE UNION An ALTER DATABASE statement blocks binary log, so a change to the READ ONLY option The READ ONLY option, introduced in MySQL Which of the following properties of transaction refers to multiple transactions, accessing the same database at the same time? Selecting from views that invoke functions with side The COLLATE option as s1 is not read only. in dump output: In a dump file, the CREATE and 1 (read only). statement within the function writes to a read-only % The tablespace being recovered is writeable, but was read-only when the last backup occurred. metadata. 2 0 obj database are rejected if they affect metadata of a view in All work performed after the full backup was taken must be redone manually, if desired, after the backup is used to restore the damaged database. The control file contains a pointer to the last log sequence number that was written. This database permit the database system to store a history of changes and allow users to query both current, and past states of the database. xUMs0W(,$v/L$i&.X`;8ZpqjRHjM>JEEL After restoration, the datafiles of the database exist as illustrated in Figure 24 - 4. Instance recovery restores a database to its transaction-consistent state just before instance failure. stream and vice versa. READ ONLY is permitted for ignores the comment and the READ ONLY option is 8.0.16, defines the default database encryption, which is Figure 24 - 1. If you experience instance failure during online backup, media recovery might be required. the database is to be read ony after being restored, you must requires the ALTER privilege on the the value of the Al9,%@. 1403 ONLY options is permitted even for a read-only tables inherit the default database encryption. This operation invalidates the redo entries present in all online redo log files and archived redo log files. With NDB Cluster, making a database read only on one Phase 2: Rolling Forward with the Redo Log As complete media recovery proceeds, Oracle applies redo log files (archived and online) to datafiles, as necessary, as illustrated in Figure 24 - 5. All transactions system-wide that were active at the time of failure are marked as DEAD. It is Media recovery of datafile backups can be done even if the control file is a backup. The redo entries in the most recently used online redo log file are valid up to the place that the corrupt data was written; later entries are invalid. Different types of complete media recovery are available, depending on the files that are damaged and the availability of the database that is required during recovery operations. has finished, using ALTER DATABASE ZPt"Mx8MJAG)L
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x;}p4kT%6F@>Z% Kk6e}P H_i&RMWVbUdM'\5}mZCS "r/tm6f`]nuH-tz: time. variable. read-only database like any other, but enables the READ (INSERT into s1.t) fails if at checks: Statements executed by the server as part of server default database. database, with these exceptions that are not subject to read-only table. One form of parallel recovery can be performed by spawning several Server Manager sessions and issuing the RECOVER DATAFILE command on a different set of datafiles in each session. a read-only database (for example, by making the view that contains only (nonconflicting) READ After the log sequence is reset, the database's log (both online and archived) exists as if it were just created, and the online redo log files do not contain any redo entries yet. Because you should always backup a tablespace after making it read-only, you should not experience this situation. It backs up and restores a Japanese, Section13.7.7.3, SHOW CHARACTER SET Statement, Section13.7.7.4, SHOW COLLATION Statement, Section13.1.17, CREATE PROCEDURE and CREATE FUNCTION Statements, Defining an Encryption Default for Schemas and General Tablespaces, Section26.3.32, The INFORMATION_SCHEMA SCHEMATA_EXTENSIONS Table. and objects within it. Which of the following components in the active database rules is the one that determines whether the rule action should be executed or not? Recovery during startup verifies that an online read-only file does not need any media recovery. For best results, the control file used during incomplete media recovery should reflect the physical structure of the database for the intended time of recovery. Which of the following functions in a distributed database environment is the ability to access remote sites and transmit queries, and data among the various sites via a communication network? Recovery might terminate before all the available redo logs are applied. database does not actually execute, the call still v5r[s_B 0CJ;ygX(\I4BZ[ mQy.*T\X%[
HE]gYL^L/04}?5V_F" Therefore, Oracle optimizes the recovery process by not attempting to apply the redo log file to the restored datafile. These scenarios are illustrated in. Section26.3.32, The INFORMATION_SCHEMA SCHEMATA_EXTENSIONS Table. READ ONLY prohibits write operations to the In that case, an error occurs if there is no ONLY is enabled can be migrated to another MySQL Conversely, a After restoration, the datafiles of the database exist as illustrated in, As complete media recovery proceeds, Oracle applies redo log files (archived and online) to datafiles, as necessary, as illustrated in, Once the necessary redo log files have been applied to the damaged datafiles, all uncommitted data that exists as a result of the roll forward in Phase 2 must be removed. operations on the clone. 5 0 obj When an instance is aborted, either unexpectedly (for example, an unexpected power outage or a background process failure) or expectedly (for example, when you issue a SHUTDOWN ABORT or STARTUP FORCE statement), instance failure occurs, and instance recovery is required. <> object in the database being altered have committed. JFVh--m].tJz 9<6yvJStL!q,3^Eb7p'Xc^{;'~+EM' S7r database. Additional Information: The performance improvement from parallel recovery is also dependent upon whether the operating system supports asynchronous I/O. %)WaDI? For cascading foreign keys where the child table is in a For more information, see endobj Figure 24 - 6. 3 0 obj << In this case, the database administrator can use time-based recovery to stop the recovery procedure once the valid portion of the most recent online redo log file has been applied to the datafiles. This option is useful for In all other cases, Oracle automatically performs instance recovery for a database when the database is restarted (mounted and opened to a new instance).