Chapter 40: The Hitchhiker’s Guide to Database Administration 821 ORACLE Series TIGHT / Oracle9 i : The Complete Reference / Loney, Koch / 222521-1 / Chapter 40 Blind Folio 40:821 is actively used by the database is backed up. These files provide a complete image of the database as it existed at the moment it was shut down. NOTE You should not rely on an offline backup performed following a shutdown abort, since it may be inconsistent. If you must perform a shutdown abort, you should restart the database and perform a normal shutdown or a shutdown immediate or a shutdown transactional prior to beginning your offline backup. The following files should be backed up during cold backups: ■ All datafiles ■ All control files ■ All online redo logs You may optionally choose to back up the database initialization parameter file, particularly if the backup will serve as the basis for a disaster recovery process. Having all of these files backed up while the database is closed provides a complete image of the database as it existed at the time it was closed. The full set of these files could be retrieved from the backups at a later date and the database would be able to function. It is not valid to perform a file system backup of the database while it is open unless an online backup is being performed (as discussed later in this chapter). Ideally, all of the datafiles are located in directories at the same level on each device. For example, all database files may be stored in an instance-specific subdirectory under an /oracle directory for each device (such as /db01/oracle/MYDB). Directories such as these should contain all of the datafiles, redo log files, and control files for a database. The only file you may optionally add to the offline backup that will not be in this location is the production initialization parameter file, which should be in either the /app/oracle/admin/ INSTANCE_NAME /pfile subdirectory under the Oracle software base directory or the /database directory under the Oracle software home directory. If you use the directory structure in the prior example, your backup commands are greatly simplified, since you will be able to use wildcards in the filenames. After shutting down the database, back up the files to the backup destination area (either a tape or a separate disk area). NOTE If necessary, you can also back up the init.ora and config.ora files at the same time. Since offline backups involve changes to the database’s availability, they are usually scheduled to occur at night. Offline backups are very reliable. To reduce their impact on the database’s availability, you may use online backups. As described in the following section, online backups use Oracle’s ARCHIVELOG mode to allow consistent file system backups during database usage. P:\010Comp\Oracle8\521-1\CD\Ventura\book.vp Friday, July 19, 2002 4:15:39 PM Color profile: Generic CMYK printer profile Composite Default screen 822 Part VI: Hitchhiker’s Guides ORACLE Series TIGHT / Oracle9 i : The Complete Reference / Loney, Koch / 222521-1 / Chapter 40 Blind Folio 40:822 Online Backups You can use online backups for any database that is running in ARCHIVELOG mode. In this mode, the online redo logs are archived, creating a full log of all transactions within the database. Oracle writes to the online redo log files in a cyclical fashion; after filling the first log file, it begins writing to the second log until that one fills, and then begins writing to the third. Once the last online redo log file is filled, the LGWR (Log Writer) background process begins to overwrite the contents of the first redo log file. When Oracle is run in ARCHIVELOG mode, the ARC0-ARC9 (Archiver) background processes make a copy of each redo log file before overwriting it. These archived redo log files are usually written to a disk device. The archived redo log files may also be written directly to a tape device, but this tends to be very operator-intensive. You can perform file system backups of a database while that database is open, provided the database is running in ARCHIVELOG mode. An online backup involves setting each tablespace into a backup state, backing up its datafiles, and then restoring the tablespace to its normal state. NOTE When using the Oracle-supplied RMAN utility, you do not have to place each tablespace into a backup state. The utility will put the tablespace into and take it out of the backup state automatically. The database can be fully recovered from an online backup, and can, via the archived redo logs, be rolled forward to any point in time. When the database is then opened, any committed transactions that were in the database at that time will have been restored and any uncommitted transactions will have been rolled back. While the database is open, the following files are backed up: ■ All datafiles ■ All archived redo log files ■ One control file, via the alter database command Online backup procedures are very powerful for two reasons. First, they provide full point-in-time recovery. Databases that are not running in ARCHIVELOG mode can only be recovered to the point in time when the backup occurred. Second, they allow the database to remain open during the file system backup. Thus, even databases that cannot be shut down due to user requirements can still have file system backups. Getting Started To make use of the ARCHIVELOG capability, the database must first be placed in ARCHIVELOG mode. The following listing shows the steps needed to place a database in ARCHIVELOG mode. Run SQLPLUS and mount the database (providing its name in place of “mydb” in these examples), then alter it as shown here: SQL> connect system/manager as sysdba SQL> startup mount mydb; SQL> alter database archivelog; SQL> alter database open; P:\010Comp\Oracle8\521-1\CD\Ventura\book.vp Friday, July 19, 2002 4:15:39 PM Color profile: Generic CMYK printer profile Composite Default screen Chapter 40: The Hitchhiker’s Guide to Database Administration 823 ORACLE Series TIGHT / Oracle9 i : The Complete Reference / Loney, Koch / 222521-1 / Chapter 40 Blind Folio 40:823 The following command will display the current ARCHIVELOG status of the database from within SQLPLUS: archive log list NOTE To see the currently active online redo log and its sequence number, query the V$LOG dynamic view. To change a database back to NOARCHIVELOG mode, use the following set of commands after shutting down the database: SQL> connect system/manager as sysdba SQL> startup mount mydb; SQL> alter database noarchivelog; SQL> alter database open; A database that has been placed in ARCHIVELOG mode will remain in that mode until it is placed in NOARCHIVELOG mode. The location of the archived redo log files is determined by the settings in the database’s parameter file. The parameters to note in Oracle9i are as follows (with sample values): log_archive_dest_1 = /db01/oracle/arch/CC1/arch log_archive_dest_state_1 = ENABLE log_archive_start = TRUE log_archive_format = arch%s.arc In this example, the archived redo log files are being written to the directory /db01/oracle/arch/CC1. The archived redo log files will all begin with the letters “arch,” followed by a sequence number. For example, the archived redo log file directory may contain the following files: arch_170.arc arch_171.arc arch_172.arc Each of these files contains the data from a single online redo log. They are numbered sequentially, in the order in which they were created. The size of the archived redo log files varies, but does not exceed the size of the online redo log files. If the destination directory of the archived redo log files runs out of space, then ARCH will stop processing the online redo log data and the database will temporarily hang. This situation can be resolved by adding more space to the archived redo log file destination disk or by backing up the archived redo log files and then removing them from this directory. NOTE Never delete archived redo log files until you have backed them up and verified that you can restore them successfully. P:\010Comp\Oracle8\521-1\CD\Ventura\book.vp Friday, July 19, 2002 4:15:39 PM Color profile: Generic CMYK printer profile Composite Default screen 824 Part VI: Hitchhiker’s Guides ORACLE Series TIGHT / Oracle9 i : The Complete Reference / Loney, Koch / 222521-1 / Chapter 40 Blind Folio 40:824 Although the initialization parameter LOG_ARCHIVE_START parameter may be set to TRUE, the database will not be in ARCHIVELOG mode unless you have executed the alter database archivelog command shown earlier in this section. Once the database is in ARCHIVELOG mode, it will remain in that mode through subsequent database shutdowns and startups until you explicitly place it in NOARCHIVELOG mode via the alter database noarchivelog command. Performing Online Database Backups Once a database is running in ARCHIVELOG mode, you can back it up while it is open and available to users. This capability allows round-the-clock database availability to be achieved while still guaranteeing the recoverability of the database. Although online backups can be performed during normal working hours, they should be scheduled for the times of the least user activity for several reasons. First, the online backups will use operating system commands to back up the physical files, and these commands will use the available I/O resources in the system (impacting the system performance for interactive users). Second, while the tablespaces are being backed up, the manner in which transactions are written to the archived redo log files changes. When you put a tablespace in “backup” mode, the DBWR process writes all of the blocks in the buffer cache that belong to any file that is part of the tablespace back to disk. When the blocks are read back into memory and then changed, they will be copied to the log buffer the first time that a change is made to them. As long as they stay in the buffer cache, they will not be recopied to the online redo log file. This will use a great deal more space in the archived redo log file destination directory. The command file for a hot backup has three parts: 1. A tablespace-by-tablespace backup of the datafiles, which in turn consists of a. Setting the tablespace into backup state b. Backing up the tablespace’s datafiles c. Restoring the tablespace to its normal state 2. Backup of the archived redo log files, which consists of a. Recording which files are in the archived redo log destination directory b. Backing up the archived redo log files, then (optionally) deleting or compressing them 3. Backup of the control file via the alter database backup controlfile command. NOTE The online backup process is automated via the RMAN utility. You should create a script to perform the backups. The script should run at the operating system level, with SQLPLUS commands executed for Steps 1a, 1c, and 3. P:\010Comp\Oracle8\521-1\CD\Ventura\book.vp Friday, July 19, 2002 4:15:40 PM Color profile: Generic CMYK printer profile Composite Default screen Chapter 40: The Hitchhiker’s Guide to Database Administration 825 ORACLE Series TIGHT / Oracle9 i : The Complete Reference / Loney, Koch / 222521-1 / Chapter 40 Blind Folio 40:825 When the datafiles are being backed up, you may back them up directly to tape or to disk. If you have enough disk space available, choose the latter option, since it will greatly reduce the time necessary for the backup procedures to complete. Recovery Manager Beginning in Oracle8.0, a Recovery Manager toolset called RMAN has been supplied to enable you to back up and recover your databases in an automated manner using either a command-line mode or the Recovery Manager from within the Oracle Enterprise Manager. You can use either approach to back up, restore, and recover database files. Recovery Manager keeps track of backups either through a Recovery Catalog or by placing the required information into the control file for the database being backed up. Recovery Manager adds new backup capabilities that are unavailable in the other Oracle backup utilities. There are four components within the Recovery Manager: the RMAN executable, one or more target databases, the Recovery catalog database, and the Media management software. The only components that you must have are the RMAN executable and a target database. Since RMAN automatically stores its metadata in the target database’s control file, you do not have to have a recovery catalog. The most significant new capability provided via Recovery Manager is the ability to perform incremental physical backups of datafiles. During a full (called a level 0 ) datafile backup, all of the blocks ever used in the datafile are backed up. During a cumulative ( level 1 ) datafile backup, all of the blocks used since the last full datafile backup are backed up. An incremental ( level 2 ) datafile backup backs up only those blocks that have changed since the most recent cumulative or full backup. You can define the levels used for incremental backups. The ability to perform incremental and cumulative backups of datafiles may greatly improve the performance of backups. The greatest performance improvements will be realized by very large databases in which only a small subset of a large tablespace changes. Using the traditional backup methods, you would need to back up all of the datafiles in the tablespace. Using Recovery Manager, you only back up the blocks that have changed since the last backup. During database recovery using Recovery Manager, you need to know which files are current, which are restored, and the backup method you plan to use. If you use the recover catalog, Recovery Manager stores its catalog of information in an Oracle database—and you need to back up that database or else you may lose your entire backup and recovery catalog of information. Recovery Manager is only used by DBAs, who need to make the decisions regarding the Recovery Manager architecture for your environment (for example, deciding on the location of the recovery catalog). You should work with your DBA to understand the recovery options in use and their implications for database availability and recovery time. Performing a Backup with Oracle Enterprise Manager (OEM) To perform any level backup using the OEM tool, connect to the OEM Server Manager console, select the appropriate database and right-click to bring up the database options. From the database options, select the Backup option from the Backup Manager menu. The Backup Wizard will activate. P:\010Comp\Oracle8\521-1\CD\Ventura\book.vp Friday, July 19, 2002 4:15:40 PM Color profile: Generic CMYK printer profile Composite Default screen To perform a backup operation, the target database must be running and available. After the initial Welcome screen, you are prompted to select a Strategy choice. You can select a predefined backup strategy or customize your own backup strategy. OEM displays the Backup Frequency options screen with three choices: 1. A Decision Support System (DSS) with a backup frequency of once a week 2. A moderately updated system (OLTP) that is not very large with a backup frequency of every day 3. A frequently updated, medium to large database with a backup frequency of full backups weekly and incremental backups nightly The default option is a DSS system backed up once a week on Sunday. Once you have selected a strategy, you will be prompted for the time to execute the backup, and the databases to back up. To perform an immediate backup, you can choose the Customize option from the initial Strategy screen. Where to Go from Here In this chapter, you’ve seen a high-level overview of the topics that production DBAs deal with every day. In addition to the topics discussed here, DBAs monitor databases, tune databases, install software, maintain database connectivity, and many other tasks. If you are interested in learning more about those tasks, see your Oracle documentation set or the Oracle9i DBA Handbook (Oracle Press, 2001). The more developers understand about database administration, the more likely they are to build applications that take advantage of the database’s inherent capabilities. 826 Part VI: Hitchhiker’s Guides ORACLE Series TIGHT / Oracle9 i : The Complete Reference / Loney, Koch / 222521-1 / Chapter 40 Blind Folio 40:826 P:\010Comp\Oracle8\521-1\CD\Ventura\book.vp Friday, July 19, 2002 4:15:40 PM Color profile: Generic CMYK printer profile Composite Default screen ORACLE Series TIGHT / Oracle9 i : The Complete Reference / Loney, Koch / 222521-1 / Chapter 41 Blind Folio 41:827 CHAPTER 41 The Hitchhiker’s Guide to XML in Oracle P:\010Comp\Oracle8\521-1\CD\Ventura\book.vp Friday, July 19, 2002 4:15:41 PM Color profile: Generic CMYK printer profile Composite Default screen X ML (eXtensible Markup Language) is a standardized syntax for describing hierarchical data. Rather than being a programming language, XML is a universal format for structured documents and data. Its tag-based syntax will be familiar to those familiar with HTML (HyperText Markup Language) and gives it the flexibility to handle complex data. Whereas HTML tells a Web browser how to present data, XML tells applications what the data means. XML is well suited to solving data interchange problems among heterogeneous systems; database-resident data is easily accessed, converted, and stored. In this chapter, you will see an overview of the XML access methods available in Oracle9i. XML and its toolsets are evolving; see http://www.w3.org for the most current information. NOTE Thanks to Mike Holder of TUSC for his contributions to this chapter. Document Type Definitions, Elements, and Attributes In XML, application-specific tags or “elements” wrap around the data they describe. The syntax for these tags is defined in a special kind of XML document called a Document Type Definition (DTD). The DTD defines the structure for a valid XML document. The structure is strictly hierarchical. Each XML document is an instantiation of an “infoset”—the abstract data model consisting of a document and its information items. Information items are mostly elements, attributes, and content. For example, an XML infoset may contain the following: <book> <title>MY LEDGER</title> <chapter num="1"> <title>Beginning</title> <text>&chapter1;</text> </chapter> </book> In this example, the tags <book> and </book> define the starting and ending points of the infoset. The XML document describes a book named “MY LEDGER”. That book has chapters, and the first chapter’s title is “Beginning”. The text of the chapter is not stored inside the XML document; instead, a pointer is created to an external file. In addition to being a tag in the file, “title” is an element. It has content, in this example, “MY LEDGER”. As shown in this example, you can set the content of elements by providing values between tags (for the title) or within the tag (as in the chapter number setting). Elements can contain content, child elements, or both, or they may be empty. For data interchange, you should avoid creating elements that contain both content and child elements. To create an empty element, its tag would be in the format: <name/> 828 Part VI: Hitchhiker’s Guides ORACLE Series TIGHT / Oracle9 i : The Complete Reference / Loney, Koch / 222521-1 / Chapter 41 Blind Folio 41:828 P:\010Comp\Oracle8\521-1\CD\Ventura\book.vp Friday, July 19, 2002 4:15:41 PM Color profile: Generic CMYK printer profile Composite Default screen NOTE Element names are case-sensitive. Each element has exactly one parent, and a parent can have any number of children. The strict hierarchical nature of XML means that if an element starts within another element (such as “chapter” within “book”), its ending tag must precede the ending tag for the parent element. As shown in the book example, elements have attributes. For example, the chapter element has an attribute named num . The attribute value is enclosed in double quotes: <chapter num="1"> NOTE Like element names, attribute names are case-sensitive. In general, applications use element attributes for specific items (such as the chapter number) and element content for the bulk of the data (in this case, the chapter text). An XML document is said to be well-formed if the following conditions are met: ■ Every start tag has a matching end tag. ■ Elements do not overlap. ■ There is one root element. ■ Attribute values are always within quotes. ■ An element cannot have two attributes within the same name. ■ Comments and processing instructions do not appear inside tags. ■ There are no unescaped < or & signs in an element’s or attribute’s character data. These are the basic syntax rules. If an XML document conforms to these rules, it may still not be valid. To be valid, the XML document must conform to the rules of a Document Type Definition (DTD). The DTD is a formal way of describing what elements and entities may appear in an XML document, and what each element’s contents and attributes are. For example, consider the following XML document. <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE CustomerList SYSTEM "Example1.dtd"> <CustomerList> <Customer preferredCustomer=""> <ID>12345</ID> <Address> <Name>TUSC</Name> <Street>377 E BUTTERFIELD RD</Street> <City>LOMBARD</City> <State>IL</State> <Country>USA</Country> Chapter 41: The Hitchhiker’s Guide to XML in Oracle 829 ORACLE Series TIGHT / Oracle9 i : The Complete Reference / Loney, Koch / 222521-1 / Chapter 41 Blind Folio 41:829 P:\010Comp\Oracle8\521-1\CD\Ventura\book.vp Friday, July 19, 2002 4:15:42 PM Color profile: Generic CMYK printer profile Composite Default screen <ZIP_CODE>60148</ZIP_CODE> <PHONE>630-960-2909</PHONE> </Address> <CreditRating>EXCELLENT</CreditRating> <SalesRepID></SalesRepID> <RegionID>5</RegionID> <Comments>THIS IS A TEST XML DOCUMENT</Comments> <ShippingMethod>M</ShippingMethod> </Customer> </CustomerList> The first line is an XML declaration, which starts with “<?” and ends with “?>“: <?xml version="1.0" encoding="UTF-8"?> The version attribute should be set to 1.0 for now. The encoding attribute is optional; its default value is UTF-8. You can also set a third attribute, standalone . In this case, the XML document is not standalone; it has a related DTD, as specified in the second line: <!DOCTYPE CustomerList SYSTEM "Example1.dtd"> The related DTD file Example1.dtd for this example is shown in the following listing: <?xml version="1.0" encoding="UTF-8"?> <!ELEMENT CustomerList (Customer*)> <!ELEMENT Customer (ID, Address, CreditRating*, SalesRepID*, RegionID, Comments*, ShippingMethod)> <!ATTLIST Customer preferredCustomer CDATA #IMPLIED> <!ELEMENT ID (#PCDATA)> <!ELEMENT Address (Name, Street*, City, County, State, Country, ZIP_CODE, PHONE)> <!ELEMENT Name (#PCDATA)> <!ELEMENT Street (#PCDATA)> <!ELEMENT City (#PCDATA)> <!ELEMENT County (#PCDATA)> <!ELEMENT State (#PCDATA)> <!ELEMENT Country (#PCDATA)> <!ELEMENT ZIP_CODE (#PCDATA)> <!ELEMENT PHONE (#PCDATA)> <!ELEMENT CreditRating (#PCDATA)> <!ELEMENT SalesRepID (#PCDATA)> <!ELEMENT RegionID (#PCDATA)> <!ELEMENT Comments (#PCDATA)> <!ELEMENT ShippingMethod (#PCDATA)> The DTD is analogous to the control file specifications for external tables. It tells applications what they will find in the XML document—the element names and the hierarchy of elements. An XML document can have only one DTD. The syntax for the element declarations is <!ELEMENT element_name ( content_model )> 830 Part VI: Hitchhiker’s Guides ORACLE Series TIGHT / Oracle9 i : The Complete Reference / Loney, Koch / 222521-1 / Chapter 41 Blind Folio 41:830 P:\010Comp\Oracle8\521-1\CD\Ventura\book.vp Friday, July 19, 2002 4:15:42 PM Color profile: Generic CMYK printer profile Composite Default screen [...]... Series TIGHT / Oracle9i: The Complete Reference / Loney, Koch / 222521-1 / Chapter 1 Blind Folio 1:845 Other Formatting Guidelines SEE ALSO suggests other topics that are closely related to the keyword, or gives the chapter or chapters in the book that give detailed descriptions of how the keyword is used in practice Occasionally you will be referred to the Oracle manual or other reference book that... Oracle9i: The Complete Reference / Loney, Koch / 222521-1 / Chapter 41 Blind Folio 41:837 Chapter 41: The Hitchhiker’s Guide to XML in Oracle Deletes function in much the same way The following procedure takes an XML document as its input, establishes the Rating column as the key for the RATING table, and performs the delete based on the key values in the input document Note that newContext takes the table... Uniqueness is declared at the same level as the complex type definition for the “Product” element The tc: namespace is for the schema we are creating and is declared in the xsd:schema element The xsd:selector value specifies the elements to constrain (the “Product” elements), and xsd:field specifies the attribute to constrain (productID) You can use xsd:key and xsd:keyref to create references between... part of the Oracle kernel software The PL/SQL API is a wrapper that publishes the Java classes to PL/SQL (see Chapter 36) Because the XSU classes are stored in the database, you can write new stored procedures to directly access XSU’s Java classes Since there is a PL/SQL API available, XSU’s functionality can be accessed directly through SQL For example, you can generate the XML version of the RATING... declares a record variable to have the same structure as an entire row in a table (or view), or as a row retrieved by the named cursor %ROWTYPE is used as part of a variable declaration and assures that the variable will contain the appropriate fields and datatypes to handle all of the columns being fetched If [user.]table is used, the table (or view) must exist in the database To create a variable that... variable name, and %ROWTYPE with the table name, and then select a row into the record Because the variable has the same structure as the table, you can reference the fields as variable.field, using notation similar to table.column used in SQL statements select .into and fetch .into are the only methods for loading an entire record variable Individual fields within the record can be loaded using :=... of the second term's search from the score of the first term's search before comparing the result to the threshold score For CTXCAT indexes, a ‘-’ tells the text search engine to exclude the row from the result set if the term following the ‘-’ is found - (Hyphen [Form 2]) SEE ALSO FORMAT Chapter 14 command text text text DESCRIPTION EXAMPLE SQL*PLUS command continuation - continues a command on the. .. Oracle9i: The Complete Reference / Loney, Koch / 222521-1 / Chapter 41 Blind Folio 41:831 Chapter 41: The Hitchhiker’s Guide to XML in Oracle where content_model specifies what children an element can or must have and the order they are in The simplest content model is #PCDATA, which says that the element can contain only parsed character data For example: In this example, the CustomerList... variable can be used The one exception is in assigning the value NULL to a host variable, which is not supported directly, but requires the use of an indicator variable EXAMPLE int BookCount; select COUNT(*) into :BookCount from BOOKSHELF; := (Set Equal To) SEE ALSO FORMAT DECLARE, FETCH, SELECT INTO, Chapter 27 variable := expression DESCRIPTION The PL/SQL variable is set equal to the expression,... file @@ is similar to @, but differs in that @@, when used in a command file, will search for a start file in the same directory as the command file that called it (rather than in the directory you are in when you execute the command file) {} (Curly Braces) SEE ALSO CONTAINS, Chapter 24, Chapter 34 FORMAT For text searches, {} indicate that the enclosed text should be considered part of the search string . tablespace back to disk. When the blocks are read back into memory and then changed, they will be copied to the log buffer the first time that a change is made to them. As long as they stay in the buffer cache,. (OEM) To perform any level backup using the OEM tool, connect to the OEM Server Manager console, select the appropriate database and right-click to bring up the database options. From the database. prompted for the time to execute the backup, and the databases to back up. To perform an immediate backup, you can choose the Customize option from the initial Strategy screen. Where to Go from