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30.09.2015
This chapter describes tablespaces, the primary logical database structures of any Oracle database, and the physical datafiles that correspond to each tablespace.
Oracle stores data logically in tablespaces and physically in datafiles associated with the corresponding tablespace.
An Oracle database consists of one or more logical storage units called tablespaces, which collectively store all of the database's data. Each tablespace in an Oracle database consists of one or more files called datafiles, which are physical structures that conform with the operating system in which Oracle is running. A database's data is collectively stored in the datafiles that constitute each tablespace of the database. When you add another datafile to an existing tablespace, you increase the amount of disk space allocated for the corresponding tablespace.
Alternatively, you can create a new tablespace (which contains at least one additional datafile) to increase the size of a database. The size of a tablespace is the size of the datafile(s) that constitute the tablespace; the size of a database is the collective size of the tablespaces that constitute the database.
The third option for enlarging a database is to change a datafile's size or allow datafiles in existing tablespaces to grow dynamically as more space is needed. See the Oracle8i Administrator's Guide for more information about increasing the amount of space in your database. Every Oracle database contains a tablespace named SYSTEM, which Oracle creates automatically when the database is created. A small database might need only the SYSTEM tablespace; however, Oracle Corporation recommends that you create at least one additional tablespace to store user data separate from data dictionary information.
A database administrator (DBA) can create new tablespaces, add datafiles to tablespaces, set and alter default segment storage settings for segments created in a tablespace, make a tablespace read-only or read-write, make a tablespace temporary or permanent, and drop tablespaces. For a tablespace that uses the data dictionary to manage its extents, Oracle updates the appropriate tables in the data dictionary whenever an extent is allocated or freed for reuse. A tablespace that manages its own extents maintains a bitmap in each datafile to keep track of the free or used status of blocks in that datafile. Local management of extents avoids recursive space management operations, which can occur in dictionary-managed tablespaces if consuming or releasing space in an extent results in another operation that consumes or releases space in a rollback segment or data dictionary table.
Local management of extents automatically tracks adjacent free space, eliminating the need to coalesce free extents. The sizes of extents that are managed locally can be determined automatically by the system.
For the SYSTEM tablespace, you can specify EXTENT MANGEMENT LOCAL in the CREATE DATABASE command.
For a permanent tablespace other than SYSTEM, you can specify EXTENT MANGEMENT LOCAL in the CREATE TABLESPACE command. For a temporary tablespace, you can specify EXTENT MANGEMENT LOCAL in the CREATE TEMPORARY TABLESPACE command. A database administrator can bring any tablespace other than the SYSTEM tablespace online (accessible) or offline (not accessible) whenever the database is open. A tablespace is normally online so that the data contained within it is available to database users. When a tablespace goes offline, Oracle does not permit any subsequent SQL statements to reference objects contained in that tablespace. When a tablespace goes offline or comes back online, this is recorded in the data dictionary in the SYSTEM tablespace. You can bring a tablespace online only in the database in which it was created because the necessary data dictionary information is maintained in the SYSTEM tablespace of that database. Transfer of Oracle data between databases can be achieved with tools described in Oracle8i Utilities. Oracle automatically switches a tablespace from online to offline when certain errors are encountered (for example, when the database writer process, DBWn, fails in several attempts to write to a datafile of the tablespace).
If you create multiple tablespaces to separate different types of data, you take specific tablespaces offline for various procedures; other tablespaces remain online and the information in them is still available for use.
If the tablespace containing the indexes is offline, queries can still access table data because queries do not require an index to access the table data. If the tablespace containing the tables is offline, the table data in the database is not accessible because the tables are required to access the data. In summary, if Oracle has enough information in the online tablespaces to execute a statement, it will do so.
The primary purpose of read-only tablespaces is to eliminate the need to perform backup and recovery of large, static portions of a database.
Because you can only bring a tablespace online in the database in which it was created, read-only tablespaces are not meant to satisfy archiving or data publishing requirements. You can use the READ WRITE option of the ALTER TABLESPACE command to make a read-only tablespace read-write again.
See the Oracle8i Administrator's Guide for more information on changing a tablespace to read-only or read-write mode, and see the Oracle8i SQL Reference for information on the ALTER TABLESPACE command. You can drop items, such as tables and indexes, from a read-only tablespace, just as you can drop items from an offline tablespace. You cannot add datafiles to a read-only tablespace, even if you take the tablespace offline. You can manage space for sort operations more efficiently by designating temporary tablespaces exclusively for sorts. All operations that use sorts--including joins, index builds, ordering (ORDER BY), the computation of aggregates (GROUP BY), and the ANALYZE command for collecting optimizer statistics--benefit from temporary tablespaces. Temporary tablespaces provide performance improvements when you have multiple sorts that are too large to fit into memory.
For a dictionary-managed temporary tablespace, use the TEMPORARY option of CREATE TABLESPACE. You can also change a tablespace from PERMANENT to TEMPORARY or vice versa by using the ALTER TABLESPACE command for any temporary tablespace (either locally managed or dictionary-managed). See Oracle8i SQL Reference for more information on the CREATE TABLESPACE, CREATE TEMPORARY TABLESPACE, and ALTER TABLESPACE commands, and see Oracle8i Tuning for information about how to set up temporary tablespaces for sorts and hash joins. The transportable tablespace feature enables you to move a subset of an Oracle database from one Oracle database to another. In the current release, you can transport tablespaces only between Oracle databases that use the same data block size and character set, and that run on compatible platforms from the same hardware vendor. After copying the datafiles and importing the metadata, you can optionally put the tablespaces in read-write mode. See Oracle8i Administrator's Guide for details about how to move or copy tablespaces to another database.
You can transport a data set consisting of one or more tablespaces, as long as the set of schema objects in the data set is self-contained (except for object references--see "REFs"). If the data set includes a partitioned table, it must contain all of the table's partitions. The metadata that you export can include or omit information about triggers, grants, and constraints, depending on which export options you use. You can also transport tablespaces to move or copy data between Oracle databases that have different compatibility or release levels.
See Oracle8i Migration for details about how to move or copy tablespaces between Oracle releases or compatibility levels. A data mart contains a subset of corporate data that is of value to a specific business unit, department, or set of users. Oracle creates a datafile for a tablespace by allocating the specified amount of disk space plus the overhead required for the file header. For information on the amount of space required for the file header of datafiles on your operating system, see your Oracle operating system specific documentation.
The first tablespace in any database is always the SYSTEM tablespace, so Oracle automatically allocates the first datafiles of any database for the SYSTEM tablespace during database creation.
When a datafile is first created, the allocated disk space is formatted but does not contain any user data; however, Oracle reserves the space to hold the data for future segments of the associated tablespace--it is used exclusively by Oracle. The data associated with schema objects in a tablespace is physically stored in one or more of the datafiles that constitute the tablespace.
You can alter the size of a datafile after its creation or you can specify that a datafile should dynamically grow as schema objects in the tablespace grow. You can take tablespaces offline (make unavailable) or bring them online (make available) at any time, except for the SYSTEM tablespace.
You can take individual datafiles offline; however, this is normally done only during some database recovery procedures. See "Space Management in Tablespaces" for more information about locally managed tablespaces. At this point, you have designed your data mart and determined the data that will be loaded into the tables in the data mart. You will perform several of these operations using Oracle Enterprise Manager, a graphical administration tool that is part of Oracle Data Mart Suite. The data in a relational database like Oracle8 is stored physically on disk as operating system files, but the physical storage is organized internally into different logical structures. You expect your users to issue queries frequently to access the data stored in the data mart. If only one user is allowed to access and modify data, that user can change data without concern for other users modifying the same data. Oracle8 provides a mechanism to allow concurrency or simultaneous access by multiple users while still maintaining integrity of data. Database security involves allowing or not allowing users to perform actions on the database and objects within it. Such privileges are granted to users at the discretion of the other users who own the objects or by the database administrator. Some Oracle processes execute constantly in the background to ensure smooth running of the Oracle8 database.
All Oracle processes communicate information to each other by filling in structures that sit in an area of shared memory called shared global area (SGA). The term instance refers to background processes and the shared memory structures of the Oracle8 database server.
Computer networking has become more and more prevalent in current computing environments, and software must be able to take advantage of the distributed processing capabilities this provides. Client: The client is a database application, such as SQL*Plus or Oracle Discoverer, that interacts with the user through the keyboard, display devices, and pointing devices such as a mouse.
Server: The server runs the Oracle8 software and handles all functions required for data access. Redo logs: Oracle8 provides a mechanism to record all changes made to data so that work is never lost, even if the system fails.
Control files: Oracle8 records information, such as the name of the database and the size and location of the datafiles and redo logs, in the control file.
You have taken a quick look at the building blocks of the Oracle8 instance--disk files, processes, memory structures.
Oracle8 stores data in operating system files, referred to as datafiles, but imposes a logical structure on top of the physical storage. This logical structure is imposed by Oracle8 for important reasons from the point of view of a database administrator. Allocating control disk space--Each tablespace corresponds to a particular set of operating system files.
Adding more space to a database--As data is added to the database, you need to allocate more disk space to the database.
By changing the size of a datafile or allowing a datafile in an existing tablespace to grow dynamically in response to the need for added space. Limiting resource usage--Tablespaces let you specify quotas, the maximum amount of space that each user can take up. Controlling availability of logical groups of data--You can choose to make all data in a tablespace unavailable by issuing a command to take a tablespace offline, or make it available again by making the tablespace online. Removing data that is no longer needed--If you decide that you no longer need the objects in a particular tablespace, you can drop the tablespace to get rid of these objects and reclaim the disk storage used by the tablespace. A segment is a set of extents that have been allocated for a specific type of data structure. When an object needs to expand because more data is being added to it, Oracle8 adds as much space as in one extent. At this point, you probably have a good grasp of the concept of a table in a relational system. If you add data to the table or delete some of the existing data, Oracle8 makes sure that these changes are reflected in the index.
Fully indexing a large table with a traditional B-tree index can be prohibitively expensive in terms of space because the index can be several times larger than the data in the table. The advantages of using bitmap indexes are greatest for low cardinality columns: that is, columns in which the number of distinct values is small compared to the number of rows in the table. In general, you use B-tree indexes when you know that your typical query refers to the indexed column and retrieves a few rows.
Let's say that your users need to see a few columns of a specific table (EMP) that contains nationwide information for all employees in your company, and they need only to see rows that refer to the employees who are managers. Statements like INSERT or DELETE simply return a message saying whether or not the operation completed successfully. Sometimes, some of the previous steps are simplified if Oracle8 finds that an identical statement was issued previously and some information about this statement already exists. An execution plan is merely a list of steps that Oracle8 must perform to execute a DML statement. Obviously, you want data to be retrieved and processed as quickly and efficiently as possible.
One of the most important choices that the optimizer makes when it formulates the execution plan is how to retrieve data from the database, or what the access paths should be for a given statement. Index scans: An index scan retrieves data from an index based on the value of one or more columns of the index. Sort-merge join: Before the tables are joined, Oracle8 usually retrieves the data for each table by a full table scan on the tables. Nested-loop join: First, the optimizer chooses one of the tables as the outer or driving table, and therefore designates the other table as the inner table. Hash join: First, Oracle8 performs a full table scan on each of the tables and splits it into as many partitions as possible based on the available memory. Rule-based: When using the rule-based approach, the optimizer looks at the different access paths available and uses a preconfigured set of rules to rank these access paths according to the speed of execution of each path.
Cost-based: The optimizer considers available access paths and factors in information based on statistics for the tables or indexes accessed by the SQL statement to determine which path is the most efficient. Oracle Corporation recommends that you use the cost-based optimization approach for most Oracle8 applications, including all data mart applications. The statistics that are required for the cost-based approach must be compiled for each table or index that you are likely to access in a SQL statement. If you do not have enough time to analyze the entire table, you can estimate the statistics using a 20% sample size.
Parallel processing divides a large task into many smaller tasks, and executes the smaller tasks concurrently. The parallel query feature can dramatically improve performance for data-intensive operations, such as the typical queries you run against your data mart. Remember that the server process does all of the work when you issue a query to access your data. The following figures illustrate how parallel processing can help a table scan complete much faster. Decision-support applications often require that large amounts of data be summarized (rolled up) into smaller tables for use with ad hoc queries.
Because the summary table is derived from data from other tables, you do not need to use redo logging, which logs the information required to recover the database or reconstruct changes to the database in the event of a system failure. When creating a table in parallel, each of the query server processes uses the value in the storage clause that specifies the size of the initial extent of the table. As "How SQL Statements Are Processed" discussed, the optimizer determines the best execution plan for a SQL statement as part of the processing of the statement. The query coordinator process examines the operations in the execution plan to determine whether the individual operations can be made parallel. For queries involving more than one table, the query coordinator uses the greatest number specified for any table in the query. For PCTAS, the degree of parallelism is determined by what is specified in the table definition.
If you do not specify the degree of parallelism in any way, Oracle8 determines the number of disks on which the table is stored and the number of CPUs in the system and selects the smaller of these two values as the default degree of parallelism. Because data marts maintain rolling windows of historical data, you must purge old data and load new data as part of ongoing maintenance. The fastest way to load data into an Oracle8 database is by using the direct path load option of the SQL*Loader utility. To create the index in parallel, Oracle8 randomly samples the table and finds a set of index keys that equally divides the index into the same number of pieces as the degree of parallelism. When creating an index in parallel, each query server process uses an amount of space equal to the initial extent value specified in the index creation statement. You know by now that the star schema is the way that data is represented in many data warehousing applications. In this example, there would be corresponding dimension tables for Time, Product, Supplier, and stores. Oracle8 Enterprise Edition provides improved performance for star queries, using the star transformation algorithm and bitmap indexes. Partitioning enables better management of very large tables and indexes by dividing them into smaller parts. Each partition description includes a clause defining supplemental, partition-level information about the algorithm used to map rows to partitions.
For maximum availability of data, store each partition in a separate tablespace and each tablespace on one or more separate storage devices. In a decision-support system (DSS), queries on very large tables present special performance problems. For example, a query that requests data generated in the month of October 1997 can scan just the rows stored in the October 1997 partition, rather than rows generated over many years of activity. In this part of the Global Computing case study, you learn how to manage storage and schema objects. Oracle Backup Manager: Lets you back up tablespaces, administer redo logs, and create backup scripts guided by a backup wizard. In the dialog box that appears, specify that you wish to continue without connecting to the repository. Click the plus sign (+) to the left of a folder icon to expand and display the contents of a folder. As "Tablespaces, Datafiles, and Data Blocks" discussed, you can add space to the database by creating new tablespaces, adding space to existing tablespaces, or extending the datafiles associated with an existing tablespace.
First, invoke the Storage Manager and connect to it as indicated in "Logging In to Oracle Enterprise Manager Components". Typically, you create a new tablespace rather than adding space to existing tablespaces if you want to allocate a designated area for a set of objects.
To list all tablespaces, expand the Tablespaces object folder in the Storage Manager window. Let's make a quick digression to explain the other option shown, the Reuse Existing Datafile option. To specify that you want the tablespace to be extensible on demand, beyond the initial size specified, select the Auto Extend tab. From the Create Tablespace dialog box, select the Extents tab and select the Override Default Values check box to override default values. Because Chapter 5 uses the schema marty for the exercises and because that schema's tablespace, USERDATA, is too small, you need to increase the size of the USERDATA tablespace.
Two tasks remain that relate directly to the SALES fact table and for which you use Oracle Enterprise Manager.
Note that startup and shutdown are the primary operations you will perform connected as user internal. Before you shut down the database, you should create a stored configuration, particularly if you are connecting to a remote database. A stored configuration lets you create multiple configurations without the need to track initialization parameters. If you do not create a stored configuration for a remote database, you will not be able to start up the database remotely unless you copy the database initialization file from the remote system to the local system. Normal: After all user sessions connected to the database complete processing, Oracle8 ensures that all changed data is written to disk and shuts down the instance. Immediate: Oracle8 terminates user sessions and ensures that all changed data is written to disk before shutting down the instance. Abort: Oracle8 terminates all user sessions and shuts down the instance without any additional processing to write changed data to disk. The Status tab of Instance Manager shows the status of the database, including whether or not it is started. This chapter describes tablespaces, the primary logical storage structures of any Oracle database, and the physical datafiles that correspond to each tablespace.


If you are using Trusted Oracle, see the Trusted Oracle7 Server Administrator's Guide for more information about tablespaces and datafiles in that environment. A database administrator can create new tablespaces, add and remove datafiles from tablespaces, set and alter default segment storage settings for segments created in a tablespace, make a tablespace read-only or writeable, make a tablespace temporary or permanent, and drop tablespaces. Every Oracle database contains a tablespace named SYSTEM that Oracle creates automatically when the database is created. A small database might need only the SYSTEM tablespace; however, it is recommended that you create at least one additional tablespace to store user data separate from data dictionary information.
Alternatively, a database administrator can create a new tablespace (defined by an additional datafile) to increase the size of a database. The size of a tablespace is the size of the datafile(s) that constitute the tablespace, and the size of a database is the collective size of the tablespaces that constitute the database. The third option is to change a datafile's size or allow datafiles in existing tablespaces to grow dynamically as more space is needed.
For more information about increasing the amount of space in your database, see the Oracle7 Server Administrator's Guide.
A database administrator can bring any tablespace (except the SYSTEM tablespace) in an Oracle database online (accessible) or offline (not accessible) whenever the database is open. Note: The SYSTEM tablespace must always be online because the data dictionary must always be available to Oracle.
When a tablespace goes offline, Oracle does not permit any subsequent SQL statements to reference objects contained in the tablespace. When a tablespace goes offline or comes back online, it is recorded in the data dictionary in the SYSTEM tablespace. Oracle automatically changes a tablespace from online to offline when certain errors are encountered (for example, when the database writer process, DBWR, fails in several attempts to write to a datafile of the tablespace). By using multiple tablespaces to separate different types of data, the database administrator can also take specific tablespaces offline for certain procedures, while other tablespaces remain online and the information in them is still available for use. In summary, if Oracle determines that it has enough information in the online tablespaces to execute a statement, it will do so. Note: Because you can only bring a tablespace online in the database in which it was created, read-only tablespaces are not meant to satisfy archiving or data publishing requirements. You cannot add datafiles to a tablespace that is read-only, even if you take the tablespace offline. Space management for sort operations is performed more efficiently using temporary tablespaces designated exclusively for sorts.
For more information on the CREATE TABLESPACE and ALTER TABLESPACE Commands, see Chapter 4 of Oracle7 Server SQL Reference.
When a datafile is created for a tablespace, Oracle creates the file by allocating the specified amount of disk space plus the overhead required for the file header. Additional Information: For information on the amount of space required for the file header of datafiles on your operating system, see your Oracle operating system specific documentation.
Since the first tablespace in any database is always the SYSTEM tablespace, Oracle automatically allocates the first datafiles of any database for the SYSTEM tablespace during database creation. After a datafile is initially created, the allocated disk space does not contain any data; however, Oracle reserves the space to hold only the data for future segments of the associated tablespace -- it cannot store any other program's data.
The data in the segments of objects (data segments, index segments, rollback segments, and so on) in a tablespace are physically stored in one or more of the datafiles that constitute the tablespace. You can alter the size of a datafile after its creation or you can specify that a datafile should dynamically grow as objects in the tablespace grow.
For more information about resizing datafiles, see the Oracle7 Server Administrator's Guide. You can take tablespaces offline (make unavailable) or bring them online (make available) at any time. For a permanent tablespace, you can specify EXTENT MANAGEMENT LOCAL in the CREATE TABLESPACE statement. For a temporary tablespace, you can specify EXTENT MANAGEMENT LOCAL in the CREATE TEMPORARY TABLESPACE statement.
Currently the functionality to create a SYSTEM tablespace as locally managed is not supported. Oracle automatically switches a tablespace from online to offline when certain errors are encountered.
You can use the READ WRITE clause of the ALTER TABLESPACE statement to make a read-only tablespace read-write again.
All operations that use sorts--including joins, index builds, ordering (ORDER BY), the computation of aggregates (GROUP BY), and the ANALYZE statement for collecting optimizer statistics--benefit from temporary tablespaces. For a dictionary-managed temporary tablespace, use the TEMPORARY clause of CREATE TABLESPACE. You can also change a tablespace from PERMANENT to TEMPORARY or vice versa by using the ALTER TABLESPACE statement for any temporary tablespace (either locally managed or dictionary-managed). You can transport a data set consisting of one or more tablespaces, as long as the set of schema objects in the data set is self-contained. CREATE TABLESPACE 'tablespace name' DATAFILE 'path - check the path of listed tablespaces' SIZE ? Once you creates all tablespaces same as like in source server then create user in new server.
Since the article provides a link to an Enterprise Edition and explains it's installation I believe it's critical to understand that this version is not free to use like for example Express Editions often are.
After launching the Oracle Installer, the Configure Security Updates screen is your first stop. The Installation Option screen lets you chose whether you want to Create and configure a database (sample database), Intall database software only, or Upgrade an existing database. The System Class screen lets you chose whether you want to install a Desktop class (ideal for develoers to play around in) or a Server class. The Oracle Home User Selection screen lets you chose whether you want to Use Existing Windows User (that’s fine if you created one previously), Create New Windows User (what I’ll do next), or Use Windows Built-in Account.
The Oracle Home User Selection screen lets you Create New Windows User, and that’s what I’ve done with the oracle user (it could be whatever you like). The Database Configuration Assistant screen tells you that you’ve been successful to this point.
The second Database Configuration Assistant screen lets you configure passwords for the database accounts. The Install Product screen reappears while most of the database cloning operation has finished. You can back up and restore an Oracle database by using the Repository Tools utility, known as repotools, that is included with the IBM Rational Software Architect Design Manager. See the Rational Application Developer Information Center.Check the IBM Rational Collaborative Design Management information center, where you can search for repotools, and explore the featured help topics.
The first time you sign in to developerWorks, a profile is created for you, so you need to choose a display name. Keep up with the best and latest technical info to help you tackle your development challenges.
Offline Normal: A tablespace can be taken offline normally if no error conditions exist for any of the datafiles of the tablespace. Offline Temporary: A tablespace can be taken offline temporarily, even if there are error conditions for one or more files of the tablespace. Offline Immediate: A tablespace can be taken offline immediately, without the database taking a checkpoint on any of the datafiles. If you absolutely have to take a tablespace offline then you should use the NORMAL clause (default) if possible. In case you are creating a temporary and undo tablespace then this step is not necessary as it involves compression of tablespace which can only be done in permanent tablespace unlike undo or temporary tablespace. You accomplish this by altering existing files or by adding files with dynamic extension properties. Tablespaces are divided into logical units of storage called segments, which are further divided into extents (see Chapter 4, "Data Blocks, Extents, and Segments"). If the database will contain many of these program units, the database administrator needs to allow for the space they use in the SYSTEM tablespace. This gives you more flexibility in various database administration operations and reduces contention among dictionary objects and schema objects for the same datafiles.
If the SYSTEM tablespace is locally managed, other tablespaces in the database can be dictionary-managed but you must create all rollback segments in locally-managed tablespaces. The SYSTEM tablespace is always online when the database is open because the data dictionary must always be available to Oracle. Active transactions with completed statements that refer to data in that tablespace are not affected at the transaction level.
If a tablespace was offline when you shut down a database, the tablespace remains offline when the database is subsequently mounted and reopened. Oracle never updates the files of a read-only tablespace, and therefore the files can reside on read-only media, such as CD ROMs or WORM drives. You can change the tablespace to read-only with the READ ONLY option of the ALTER TABLESPACE command, making all of the tablespace's associated datafiles read-only as well. READ ONLY command places the tablespace in a transitional read-only mode and waits for existing transactions to complete (commit or roll back).
Also, should you need to recover your database, you do not need to recover any read-only tablespaces, because they could not have been modified. When you add a datafile, Oracle must update the file header, and this write operation is not allowed in a read-only tablespace. Doing so effectively eliminates serialization of space management operations involved in the allocation and deallocation of sort space. One sort segment exists for every instance that performs a sort operation in a given tablespace. The sort segment of a given temporary tablespace is created at the time of the first sort operation. See "Space Management in Tablespaces" for information about locally managed and dictionary-managed tablespaces. You can clone a tablespace from one tablespace and plug it into another database, copying the tablespace between databases, or you can unplug a tablespace from one Oracle database and plug it into another Oracle database, moving the tablespace between databases. When you transport tablespaces you can also move index data, so that you do not have to rebuild the indexes after importing or loading the table data. If you transport a data set that contains a pointer to a BFILE, you must also move the BFILE and set the directory correctly in the target database. To transport a subset of a partitioned table, you can exchange the partitions into tables before transporting them. Typically, data flows from one or more online transaction processing (OLTP) databases into the data warehouse on a monthly, weekly, or daily basis. For example, a content provider might acquire statistical data from hospitals and provide it to insurance companies, or a telephone company might give large customers their billing data on CDs.
When a datafile is created, the operating system in which Oracle is running is responsible for clearing old information and authorizations from a file before allocating it to Oracle. As the data grows in a tablespace, Oracle uses the free space in the associated datafiles to allocate extents for the segment. Note that a schema object does not correspond to a specific datafile; rather, a datafile is a repository for the data of any schema object within a specific tablespace. This functionality enables you to have fewer datafiles per tablespace and can simplify administration of datafiles.
All of the datafiles making up a tablespace are taken offline or brought online as a unit when you take the tablespace offline or bring it online, respectively.
You can also perform all of these operations by issuing SQL commands in a utility called Server Manager. You store the data for the data mart in an Oracle8 database, which lets multiple users access the data quickly and efficiently and protects the data against system failure. Oracle8 provides a way to create these structures and manage them as data is added, changed, or deleted.
Oracle8 maintains a record of all changes so that these changes can be recovered even if the computer crashes while changes are still in memory and have not been written to permanent storage.
However, in real life, many users running multiple applications at the same time can update the same data. Primarily, Oracle8 uses locks on data to prevent destructive interaction between users accessing the same data. Through the use of privileges, Oracle8 provides a way to regulate all access by users to all objects.
Think of the SGA as the message board in your kitchen where you leave messages for other people in your house.
Distributed processing means that a set of related jobs is divided among several computers, instead of using one computer to run them all. The client concentrates on requesting and presenting data, which is retrieved from the database by the server. You can think of the control file as the place where Oracle8 stores some important bookkeeping information about the database.
By specifying which tablespace an object should be created in, you can group related objects in one set of datafiles. However, you also want to control the operating system files from which this space is allocated.
You can back up and recover tablespaces and make tablespaces read-only so that you can query objects in them but cannot modify data. You can think of tablespaces as pools of available space organized into smaller units called data blocks.
For example, data for each table is stored in its own data segment, while data for each index is stored in its own index segment. When the existing extents of a segment are full, Oracle8 allocates another extent for that segment.
Within a tablespace, a segment can span datafiles (have extents with data from more than one file).
In the example of the table joe_table in tablespace JOE_DATA, the table initially contains 1000 rows of data contained in one extent of size 1 MB. You create an index on a table to speed up the execution of SQL statements that refer to that table.
Bitmap indexing benefits data warehousing applications, which have large amounts of data and ad hoc queries but a low level of concurrent transactions.
If the values in a column are repeated more than a hundred times, the column is a candidate for a bitmap index. The bottommost level of the index holds the actual data values and pointers to the corresponding rows, much like the index in a book has a page number associated with each index entry. Instead of requiring your users to create a query repeating these criteria every time they need to access this information, you might create a view. This section describes how you can make SQL queries execute in the fastest possible time, but first it explains how the Oracle8 database server processes a SQL statement. A SQL statement can be a query that simply selects data from the database according to a set of criteria, or a statement that changes existing data, adds data to the database, or deletes data from the database. Each step retrieves data from the database or prepares it for the user issuing the statement. The process of choosing the most efficient way to execute a SQL statement is called optimization.
For example, when you use a tool like SQL*Plus to connect to the database, the process that is associated with the tool is the front-end (client) process.
For any row in any table accessed by a SQL statement, there may be many access paths by which that row can be located and retrieved.
To perform a full table scan, Oracle8 reads all rows in the table, examining each row to determine whether it satisfies the statement's conditions or WHERE clauses. To perform an index scan, Oracle8 searches the index for the indexed column values that are mentioned in the SQL statement. A join is characterized by multiple tables being listed in the FROM clause of the SQL statement.
Next, for each row in the outer table, Oracle8 finds all rows in the inner table that satisfy the join condition. Then, Oracle8 builds an internal structure called a hash table from one of the partitions and uses the corresponding partition in the other table to probe the hash table. These statistics are stored in the data dictionary tables and quantify the data distribution and storage characteristics of tables and indexes. If the table is small enough, Oracle8 can sort it in memory, but more often, the table is too big to be sorted entirely in memory.
Note, however, that estimating the computation may not give you the optimal query performance.
Systems with multiple CPUs, such as SMP systems, gain the largest performance benefit from the parallel query feature because query processing can be effectively split up among the many CPUs.
The server process retrieves the data from the database and sends the results to the client process for display.
The query coordinator breaks down the execution of the full table scan into parallel pieces. Therefore, a table created with a degree of parallelism of 12 and an initial extent of 1 MB consumes at least 12 MB of storage during table creation because each process starts with an extent of 1 MB.
After the execution plan is determined, the query coordinator process determines the parallel execution method; that is, which operations can be performed in parallel.
All of the listed factors determine only how many query servers the query coordinator requests, not necessarily how many are finally used in processing the query. If no degree of parallelism is specified, the degree of parallelism is derived from the parallelism of the subquery. Direct path load eliminates much of the Oracle8 database overhead by writing directly to the database files. This means that it can become difficult to finish administrative operations like loading data and re-creating indexes in finite batch windows unless index creation can be speeded up in proportion to the growth in data volume. A first set of query processes scans the table, extracts the index key and row location information, and sends this to a process in a second set of server processes based on key.
Therefore, you should make sure that an adequate amount of space is available in the tablespace that holds the index. The star schema has one or more very large fact tables containing the primary information in the data warehouse, and a number of much smaller dimension tables, each of which contains information about the entries for a particular attribute in the fact table. For example, a star schema in a retail environment could have a simple fact table containing the measure Sales that records the amount of total sales for each sales transaction, and the keys Time, Product, Supplier, and stores. The PRODUCT dimension, for example, would typically contain information about each product that appears in the fact table. In a star query, each of the dimension tables is joined to the fact table using a primary key to foreign key join called the star join. The star transformation is a cost-based query transformation that can process star queries with large or many dimension tables, unconstrained dimension tables, and dimension tables that have a snowflake schema design. Partitioned tables and indexes can improve availability, ease administration, and enhance query performance in your data mart. You choose to partition your fact table based on the time period, with one partition for each four-week period. An ad hoc query that requires a table scan may take a long time, because it must inspect every row in the table.
An ad hoc query that only requires rows that correspond to a single partition (or range of partitions) can be executed using a partition scan rather than a table scan. You use the database named DMDB, which contains one file each for the tablespaces System, Userdata, Rollback, and Temp.
These exercises assume that you chose the standard installation and therefore automatically have an Enterprise Manager repository in the DMDB instance. The display on the right side of the window is determined by the objects selected from the tree list on the left side of the window.
In this exercise, you create a new tablespace called YVES_DATA and associate it with a datafile. When you drop a tablespace, the Oracle8 database server does not automatically delete the corresponding datafiles. The values specified in the next step have been chosen with a data mart application in mind. However, you may need to know how to manually start up and shut down the database instance. The Instance Manager stores the configuration in the Windows NT Registry on the local machine.
Instead, Oracle8 will postpone making changes permanent until the database is next opened up. The list box displays the name of the configuration that you created in the previous section. For example, suppose you create a table in a specific tablespace using the CREATE TABLE command with the TABLESPACE option. This allows you more flexibility in various database administration operations and can reduce contention among dictionary objects and schema objects for the same datafiles. You can add another datafile to one of its existing tablespaces, thereby increasing the amount of disk space allocated for the corresponding tablespace. Active transactions with completed statements that refer to data in a tablespace that has been taken offline are not affected at the transaction level.


The READ ONLY option of the ALTER TABLESPACE command allows you to change the tablespace to read-only, making all of its associated datafiles read-only as well. When you add a datafile, Oracle must update the file header, and this write operation is not allowed. This scheme effectively eliminates serialization of space management operations involved in the allocation and deallocation of sort space. When a datafile is created, the operating system is responsible for clearing old information and authorizations from a file before allocating it to Oracle. As a segment (such as the data segment for a table) is created and grows in a tablespace, Oracle uses the free space in the associated datafiles to allocate extents for the segment.
Note that a schema object does not correspond to a specific datafile; rather, a datafile is a repository for the data of any object within a specific tablespace.
This functionality allows you to have fewer datafiles per tablespace and can simplify administration of datafiles. Therefore, all datafiles making up a tablespace are taken offline or brought online as a unit when you take the tablespace offline or bring it online, respectively. The size of a database is the collective size of the tablespaces that constitute the database.
Tablespaces are divided into logical units of storage called segments, which are further divided into extents. For example, Oracle switches a tablespace from online to offline when the database writer process, DBWn, fails in several attempts to write to a datafile of the tablespace.
You can change the tablespace to read-only with the READ ONLY clause of the ALTER TABLESPACE statement, making all of the tablespace's associated datafiles read-only as well. READ ONLY statement places the tablespace in a transitional read-only mode and waits for existing transactions to complete (commit or roll back).
A temporary tablespace is not the same as a tablespace that a user designates for temporary segments, which can be any tablespace available to the user.
The new data can become a partition of the historical data by exchanging tables with partitions. You may provide your email (attached to your Oracle Support Contract) and Oracle Support password, or uncheck the box and you can simply install a Desktop test environment.
Check the appropriate radio button and then click the Next button to proceed with the install. Read it over, save a copy for later, and when everything is right then click the Next button to install.
Don’t walk away too quickly because you’re most likely going to have to allow access for the installation to complete successfully. Although, this is where several errors can occur when you failed to correctly configure Windows 7 before installation.
The article presents a scenario in which a user backs up the Oracle database, uninstalls and then reinstalls Design Manager, restores, configures, and deploys Design Manager on WebSphere Application Server, and then restores the database. He has run both system and functional verification test levels, as well as all aspects IBM Rational modeling tools, including Rational Rose, Rational Rose RealTime, and Rational Software Architect. Your display name must be unique in the developerWorks community and should not be your email address for privacy reasons. In this situation graphic user tools always comes handy where they do all the dirty work and we do not have to remember anything. When you specify OFFLINE TEMPORARY, the database takes offline the datafiles that are not already offline, check pointing them as it does so. When you specify OFFLINE IMMEDIATE, then the media recovery for the tablespace is required before the tablespace can be brought online. This ensures that in case of an incomplete recovery while resetting the redo log sequence using an ALTER DATABASE OPEN RESETLOGS statement, the tablespace does not require recovery to be online. Here you can see the CREATE TABLESPACE statement with all the settings done by you using SQL Developer gui. Another database might have three tablespaces, each consisting of two datafiles (for a total of six datafiles).
When an extent is allocated or freed for reuse, Oracle changes the bitmap values to show the new status of the blocks. Oracle saves rollback data corresponding to those completed statements in a deferred rollback segment (in the SYSTEM tablespace).
This transitional state does not allow any further write operations to the tablespace except for the rollback of existing transactions that previously modified blocks in the tablespace.
However, read-only tablespaces may need attention during instance or media recovery, depending upon whether and when they have ever been read-write. The sort segment expands by allocating extents until the segment size is equal to or greater than the total storage demands of all of the active sorts running on that instance. The transport of these files can be done using any facility for copying flat files, such as the operating system copying facility, ftp, or publishing on CDs. The data is usually processed in a staging database before being added to the data warehouse. Content providers can transport tablespaces to publish structured data on CD or other media, enabling customers to integrate the published data into their Oracle databases. Oracle allocates space for the data associated with a schema object in one or more datafiles of a tablespace. Oracle8 also provides a way to back up data on disk to a safe location and restore data from these backups if the disk fails. Therefore, some mechanism needs to ensure that many users can access data at the same time and yet see a consistent view of the data.
Thus, if one user wants to change a piece of data, the data is automatically locked until the change is completed and made permanent (committed). A privilege is explicit permission to access a certain object or execute a certain type of SQL statement. This reduces the processing load on any single computer, improving the performance of the system as a whole. The client usually runs on a workstation or personal computer, which can be optimized for its job. When you create an object in a tablespace, Oracle8 allocates space from this pool to the object in chunks called extents, which consist of contiguous data blocks. Because extents are allocated as needed, the extents of a segment may or may not be contiguous on disk.
Even columns with a lower number of repetitions (and thus higher cardinality), can be candidates if they tend to be involved in complex conditions in the WHERE clauses of queries. The rest of the blocks at the upper levels provide a road map to the right block at the bottommost level. However, there is a tricky issue here--return to the analogy of a book index to understand it. This process takes input from the user, sends the SQL statement for processing, and displays the results of the SQL statement to the user. If the statement references only columns of the index, Oracle8 can read the indexed column values directly from the index, rather than from the table.
Oracle8 pairs the rows from these tables based upon the condition specified in the WHERE clause and returns the resulting rows.
It merges the two sorted sources so that each pair of rows (one from each source) that contains matching values for the columns used in the join condition is combined and returned as the join result.
Finally, Oracle8 combines the data in each pair of rows that satisfy the join condition and returns the resulting rows. For each pair of partitions (one from each table), Oracle8 uses the smaller one to build a hash table and the larger one to probe the hash table. This approach does not take into account the size of the table or index, or other issues, like how the data is distributed. You can set the init.ora parameter optimizer_mode to choose, which causes the optimizer to choose between the rule-based and cost-based approach depending on whether or not the statistics needed for the cost-based approach are present. As part of the analyze command, you can specify whether you want Oracle8 to estimate the statistics based on randomly sampling some of the data in the table or index or to compute the statistics exactly. In that case, Oracle8 sorts part of the data in memory and allocates temporary space to act as a workspace to hold the data that is not being currently processed in memory.
The parallel query feature allows the operations listed to be performed by multiple processes. Often, such rollup operations must occur regularly (perhaps nightly or weekly) and should happen when the system is relatively inactive. If you use the unrecoverable option to disable recoverability during parallel table creation, you should back up the tablespace containing the table after the table is created to avoid loss of the table due to media failure.
When making these decisions, the query coordinator uses information specified in the table definition, the hints that are provided in a query, the initialization parameters, and, if at least one of the operations is involved in processing, a full table scan.
You can speed up direct path loads even further by specifying that redo should not be logged. Parallel creation of indexes speeds up index creation by using multiple processes simultaneously to create an index. The SALES table would be very large because a retail chain could easily have millions of sales transactions per day. It can also efficiently process queries that contain criteria that eliminate a great number of the rows in the fact table. First, Oracle8 retrieves exactly the necessary rows from the fact table by using bitmap indexes. A partitioned table is a table that is divided (partitioned) into several smaller parts, based on a range of key values that you specify.
When you load data into the data mart, you load data (and indexes) into only one partition, rather than the entire table.
In the exercises in this section, you learn how to accomplish some common database management tasks. Subsequently, when you start up the database and select the stored configuration, the Instance Manager reads the configuration information from the registry. A more complicated database might have three tablespaces, each comprised of two datafiles (for a total of six datafiles). Oracle allocates the space for this table's data segment in one or more of the datafiles that constitute the specified tablespace. For more information about these objects and the space that they require, see Chapter 14, "Procedures and Packages", and Chapter 15, "Database Triggers". Oracle saves rollback data corresponding to statements that affect data in the offline tablespace in a deferred rollback segment (in the SYSTEM tablespace).
Thus, tablespaces cannot be transferred from database to database (transfer of Oracle data can be achieved with tools described in Oracle7 Server Utilities).
The file cannot be written to unless its associated tablespace is returned to the read-write state. All operations that use sorts, including joins, index builds, ordering (ORDER BY), the computation of aggregates (GROUP BY), and the ANALYZE command to collect optimizer statistics, benefit from temporary tablespaces. The sort segment grows by allocating extents until the segment size is equal to or greater than the total storage demands of all of the active sorts running on that instance. Oracle allocates the extents of a single segment in one or more datafiles of a tablespace; therefore, an object can "span" one or more datafiles. You can take individual datafiles offline; however, this is normally done only during certain database recovery procedures.
Because dictionary tables and rollback segments are part of the database, the space that they occupy is subject to the same space management operations as all other data. Oracle saves rollback data corresponding to those completed statements in a deferred rollback segment in the SYSTEM tablespace.
If the file is large, this process might take a significant amount of time.he first tablespace in any database is always the SYSTEM tablespace, so Oracle automatically allocates the first datafiles of any database for the SYSTEM tablespace during database creation.
Check the Rational training and certification catalog, which includes many types of courses on a wide range of topics.
When you specify OFFLINE NORMAL, the database creates a checkpoint for all datafiles of the tablespace as it takes them offline.
If no files are offline, but you use the temporary clause then media recovery is not required to bring the tablespace back online. You cannot take a tablespace offline immediately if the database is running in NOARCHIVELOG mode. TEMPORARY must be specified only if it is impossible to take the tablespace offline normally. These changes do not generate rollback information because they do not update tables in the data dictionary (except for special cases such as tablespace quota information). When the tablespace is brought back online, Oracle applies the rollback data to the tablespace, if needed.
Hence, in transition the tablespace behaves like a read-only tablespace for all user commands except ROLLBACK. The section "Understanding Oracle8 Database Server: The Building Blocks" examines some of the mechanisms that enable fast processing of queries.
Such backup mechanisms do not require you to shut off access to users--the database can be up and running while you go about the business of protecting your data. A consistent view of data in a multiuser environment means that every user sees the changes that user makes as well as changes made by other users--no changes are lost or overwritten. Any user attempting to change the same data must wait until the first user releases the lock. Oracle8 provides a read-consistency mechanism to make sure that you see data as it existed before the change began.
For example, when you try to access the Oracle8 database to perform a query, the work is done by a server process that is created to execute the actions you specify.
You specify the amount of memory to allocate to the SGA in the database parameter file, init.ora. These files are used in a cyclical way--for example, if your database has two redo logs and the first is filled, Oracle8 starts writing information into the second redo log.
To minimize the chances of this, Oracle8 lets you specify that you want to maintain multiple copies of the control file in more than one physical location. In this example, you have two users, JOE and BOB, who tend to run resource-intensive queries at the same time. Oracle8 looks at the extent already allocated to joe_table and checks if there is room left to insert the 1000 new rows.
Indexes in databases are based on a similar idea--if a column of a table has indexes, you can look up the index to find the rows of the table that have a particular data value for that column. If you plan to look at every single topic in a book, you might not want to look in the index for the topic and then look up the page. You create tables and other internal database structures using another type of SQL statement called data definition language (DDL). The process that handles the query (or any other statement that you issue), retrieves the data that is requested, and returns it to the front-end process to display to the user is called the back-end (server) process. If the statement accesses other columns in addition to the indexed columns, Oracle8 uses the address of the row, called a rowid, to find the rows in the table.
The cost-based approach also considers hints or optimization suggestions placed in the SQL statement. If statistics are available for at least one of the tables accessed by the SQL statement, the optimizer uses the cost-based approach. Thus, to compute the statistics for a table, Oracle8 could need enough disk space to scan and sort the entire table. Thus, if the distribution or location of data changes, the Oracle8 database server automatically adapts to optimize the parallelization of each SQL statement.
When Oracle8 employs parallel query processing, one process, known as the query coordinator, divides the execution of a statement among several query servers and coordinates the results from all of the servers to send the results back to the user. The number of query servers assigned to a single operation is the degree of parallelism for the query.
The parallel query feature allows you to parallelize the operation of creating a table as a subquery from another table or set of tables.
By dividing the work necessary to create an index among multiple query server processes, Oracle8 can create the index more quickly than if a single server process created the index sequentially.
After all index pieces are built, the query coordinator process concatenates all pieces to build the final index.
The problem is particularly important for historical tables, for which many queries concentrate access on rows that were generated recently. The files of a read-only tablespace can independently be taken online or offline using the DATAFILE option of the ALTER DATABASE command. One sort segment exists in every instance that performs a sort operation in a given tablespace. Unless table "striping" is used, the database administrator and end-users cannot control which datafile stores an object. Hence, in transition the tablespace behaves like a read-only tablespace for all user statements except ROLLBACK. After making a choice about what you want to do with updates, click the Next button to proceed with the install.
He recently joined the Design Manager Performance Test Team, where he conducts performance tests of both the web client and the IBM Rational Software Architect Design Manager extension. Enter a database nameFor the database credentials (Screen should read Step 5 of 12 in title bar), select Use the Same Administrative Password for All Accounts, and provide the same password as the original database.(See Figure 6. Ita€™s recommended that connection which you are adding in DBA panel must be with privileged user such as sys. However, if one or more files of the tablespace are offline because of write errors, and you take it offline temporarily, then the tablespace requires recovery before you can bring it back online. In this case, only those files that are taken offline due to errors are need to be recovered before the tablespace can be brought online. You can take the files of a read-only tablespace online or offline independently using the DATAFILE option of the ALTER DATABASE command. Unless table "striping" is used (where data is spread across more than one disk), the database administrator and end users cannot control which datafile stores a schema object. When this fills up, Oracle8 switches over to the first redo log and starts reusing the log. You need a way of separating their data so both are not accessing the same set of disks and running the risk of overloading them. Keep in mind that indexes are independent of the data in a table; they are just a fast way to get to the table data. In addition, you perform most operations to manage the database using other types of SQL statements.
Thus, most of the steps in the processing of a SQL statement are carried out by the server process. With two tellers, the task can be effectively split so that the customers form two lines and are served twice as fast. If you run parallel direct path load, keep in mind that each of the loader processes will allocate an extent of the size specified by the storage parameter next extent and appropriately size the tablespace in which the table is being created. To further increase the performance, you can specify that no redo entries be logged during index creation. This allows for better optimization of more complex star queries, such as those with multiple fact tables. See Chapter 3, "Data Blocks, Extents, and Segments", for more information about extents and segments and how they relate to tablespaces.
You can take the files of a read-only tablespace online or offline independently using the DATAFILE clause of the ALTER DATABASE statement. Unless table striping is used (where data is spread across more than one disk), the database administrator and end users cannot control which datafile stores a schema object. Using IBM Rational Performance Tester, his team creates and runs scripts for benchmark testing of releases.
Also IMMEDIATE can only be specified after both the normal and the temporary settings have been tried. You can create or drop an index at any time without affecting the table to which the index refers or any other indexes on the table. Similarly, if you are retrieving most of the rows in a table, it might not make sense to look up the index to find the table rows.
It's quick and easy.Share your knowledge and help others who use Rational software by writing a developerWorks article. By contrast, if the bank manager needs to review all loan requests, parallel processing will not necessarily speed up the flow of loans. No matter how many tellers are available to process loans, all requests must form a single queue for bank manager approval.
Setting the table space to the user nameUnder the Modify System Privileges tab, move all of the available system privileges to the selected system privileges, and then click OK. Log out of the WebSphere Application Server, and then stop and restart the server.You should now be able to log in to the projects that you had before.



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