6 storage and file structures

Offline If the tablespace has a status of Offline, then no users can access it. When the undo tablespace is auto-extensible, Oracle automatically increases the size of the tablespace when more space is needed. Although it is common to refer to tablespaces as autoextending, automatic extension is a data file property, not a tablespace property.

This topic is discussed in Chapter 9, "Performing Backup and Recovery". You can respond to size alerts by manually increasing the tablespace size. Space usage within the tablespace is such that records can be overwritten. For configuring Flashback Query and Flashback Table, set a value equal to how far back in time you need to go.

Shrinking Database Objects Over time, it is common for segment space to become fragmented or for a segment to acquire a lot of free space as the result of update and delete operations. This exercise will also familiarize you with the various attributes that you can set, and possibly later modify, for a tablespace.

The Required Tablespace Size by Undo Retention Length graph shows the relationship between retention period and undo tablespace size, highlighting key data points, such as the Auto-tuned and Best Possible Retention.

To undo any uncommitted changes made to the database in the event that a rollback operation is necessary. The Configuration section also shows if auto-extending the tablespace is enabled, which is the default. A rollback operation can be the result of a user specifically issuing a rollback statement to undo the changes of a misguided or unintentional transaction, or it can be part of a recovery operation.

Segment Advisor can also be launched from the Advisor Central page. Again, you should not need to create additional undo tablespaces.

The Undo Advisor helps you analyze various scenarios to determine an appropriate undo tablespace size for different values of maximum undo retention. Undo data is stored in a logical database structure called an undo tablespace. You would probably not create a tablespace as offline, but rather you would change its status to offline when, for example, you wanted to perform some maintenance on its underlying files.

You can encrypt any permanent tablespace to protect sensitive data.

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To build a flashback recovery strategy, you can set the minimum undo retention, which determines the lowest value for automatic undo tuning. By default, the undo tablespace is set to auto-extend when you use DBCA to configure your database. A database instance can have only one active undo tablespace.

Undo Tablespace Size and Retention Time In order for changes to be rolled back or undone, Oracle makes a copy of the original data before modifying it. When you install the database, Oracle automatically enables auto-tuning of the undo retention period.

You can specify a maximum size for an autoextending data file. This brings you back to the Edit Tablespace page. Using the Segment Advisor The Segment Advisor performs growth trend analysis on individual objects to determine if there will be any additional space left in the object in 7 days.

Extending the Undo Tablespace When auto-extend tablespace is enabled, the system automatically extends the undo tablespace if it is under space pressure. Select Shrink Options at the bottom of the page.

This situation might cause long-running queries to fail with an error and an alert. The Undo Retention Settings section describes your minimum undo retention period. Collectively these pockets can combine to form large amounts of wasted space. Managing Undo for Your Database This section discusses undo management which involves storing the changes of database transactions long enough to accommodate rollback, read consistency, and flashback features.

The Recommendations section of the Undo Management page gives you recommendations on undo tablespace size based on your system activity. Encrypted Tablespaces Encrypted tablespaces primarily protect your data from unauthorized access by means other than through the database.

You cannot add a datafile to a bigfile tablespace. You need to either set your tablespace to auto-extend or manually extend it. If you are interested in using flashback features such as Flashback Query or Flashback Table, you can use the Undo Advisor to advise on how to configure your tablespace and undo retention.

The Thresholds page appears. The preconfigured database already has a temporary tablespace. You can respond to size alerts by manually increasing the tablespace size. You might need to alter this value to build a recovery strategy using Flashback Query. However, when the auto-extend tablespace feature is disabled, you might need to manually extend the undo tablespace.

Select a datafile to extend and click Edit. Later as your database activity and transaction rate increase, understanding how to manage undo will become more useful to you.6 Managing Database Storage Structures.

Database storage structures

This chapter discusses using Oracle Enterprise Manager Database Control (Database Control) to view and manage the storage structures of your database.

This chapter contains the following sections: If the Storage Type is File System, then in the File Name field, enter a file name.

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6. Storage and File Structures Goals Understand the basic concepts underlying di erent storage media, bu er management, les structures, and organization of records in les.

Contents Overview of Physical Storage Media Magnetic Disks, Tertiary Storage Bu er Management Storage Access File Organization. Chapter 6: Managing Database Storage Structures Back to Lesson List Purpose.

Database storage structures

In this chapter you will learn how to use Enterprise Manager to explore the structure of your database. In addition, you will learn how to make a number of changes to your database storage structure.

Enter a file name in the File Name field on the Add Datafiles. 6 Managing Database Storage Structures. This chapter discusses using Enterprise Manager to explore and manage the storage structures of your database. This chapter contains the following topics: A control file tracks the physical components of the database.

It is. Database System Concepts - 6th Edition ©Silberschatz, Korth and Sudarshan Chapter Storage and File Structure Overview of Physical Storage Media Magnetic Disks RAID Tertiary Storage Storage Access File Organization Organization of Records in Files Data-Dictionary Storage. 6 Chapter 10 Storage and File Structure bits.

Note that we don’t need to access the bitmaps at all unless the usage crosses a boundary, so .

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