About Database Storage Structures
Figure 1  shows the relationship between these physical structures and the logical storage structures. One Oracle datafile corresponds to one physical. Let's examine the relationship of logical to physical objects. The arrow points Segments are the next logical storage structure after tablespaces. Segments are . Chapter 6. Storage Structure and Relationships Terms you'll need to understand: Table segment and table partition segment Index segment and index partition.
Allocating an extent to a particular case, the blocks are instantly apportioned to the free run down. In any case, if the extent is not permitted to a particular case, then the block itself will assigned just when the high water mark moves. The high water mark imprint the limit in the middle of utilized and vacant space as a part of a segment.
Segments Description In Oracle Storage Structures, Segment are the collections of extents that consists of over all information about a consistent stockpiling design inside the table slot. Oracle Database oversees segment space consequently or physically. Client segments Description A database stores the single data segments for single client object.
The segment are of various types. Illustrations of client segments consists: LOB or LOB partition Index or index partition Table, table partition, or table cluster Every object partition and non-allotments object are saved in individual segment.
For instance, there are five partitions consisting in index, then the index data contain five segments. Creating client segment Description As the matter of course, the database utilizes conceded update only to database metadata in segment creation while constitute indexes and tables. The Release 2 of oracle database 11g While inserting the prime row into a table by the user, then the segments for the table or partition is created by the database, its indexes and its LOB columns.
Conceded segment enables creating you to abstain from utilizing database assets superfluously. And large portion of these objects might never be utilized. Expel segments between the vacant partition or tables that presently contain unfilled portion assign. And table creation will be as follows.
Oracle 9i Fundamentals I Exam Cram™ 2 (Exam 1Z0-031) by April Wells
Conceptual figure While creating a primary key with a table ,automatically construct an index for this key by the oracle database. Again except that creation is impaired for conceded segment. The data is stored in one segment for lop table, while the segment is different for the implicitly created index and also, it stores the club data in individual segment, because CLOB index is associated.
Hence, creation of four different segments will be done by using create table. Conceptual Table space Description A logical stockpiling container for segments is called tablespace.
The are database objects are segments, like index and tables,and the storage space that it consumes. At the physical stage, information in one or more data files will be stored in the table space. Examples By viewing the below example, the concepts of table spaces can be understood easily. Conceptual Permanent table space Description A persistent schema objects are permanent table space groups. The table space containing segments for objects are stored in the information files. A default permanent table space is assigned to each client in the database.
Hence, at least one table space for application data and to store user will be created by oracle. Allots an amount to a database clients. Control disk space designation for database information. The crow's foot notation represents a one-to-many relationship. Oracle ASM disks can be added or dropped from a disk group while the database is running.
When you add a disk to a disk group, you either assign a disk name or the disk is given an Oracle ASM disk name automatically.
The data structures in a disk group are self-contained and consume some disk space in a disk group. The content of files that are stored in a disk group are evenly distributed, or striped, to eliminate hot spots and to provide uniform performance across the disks. The database can store data files, control files, online redo log files, and other types of files as Oracle ASM files.
Oracle ASM files can coexist with other storage management options, such as third-party file systems. This capability simplifies the integration of Oracle ASM into pre-existing environments. You might change the status of a tablespace to Offline before performing maintenance or recovery on the data files associated with that tablespace.
Autoextend Tablespace You can set a tablespace to automatically extend itself by a specified amount when it reaches its size limit. If you do not enable autoextend, then you are alerted when the tablespace reaches its critical or warning threshold size. The critical and warning threshold parameters have default values that you can change at any time. These parameters also cause alerts to be generated for autoextending tablespaces that are approaching their specified size limit.
You can respond to size alerts by manually increasing the tablespace size. You do so by increasing the size of one or more of the tablespace data files or by adding another data file to the tablespace. Although it is common to refer to tablespaces as autoextending, automatic extension is a data file property, not a tablespace property. That is, when you create the data files that comprise a tablespace, you indicate whether these data files automatically extend.
A tablespace that has autoextending data files is considered to be an autoextending tablespace.
Managing Database Storage Structures
You can specify a maximum size for an autoextending data file. Encrypted Tablespaces Encrypted tablespaces primarily protect your data from unauthorized access by means other than through the database. For example, when encrypted tablespaces are written to backup media for travel from one Oracle database to another or for travel to an off-site facility for storage, they remain encrypted.
Also, encrypted tablespaces protect data from users who try to circumvent the security features of the database and access database files directly through the operating system file system. You can encrypt any permanent tablespace to protect sensitive data. When you encrypt a tablespace, all tablespace blocks are encrypted.