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Storage attributes


The Physical Attributes / Storage tab available in object editors lets you specify how a database object should be stored in the database. Storage parameters affect both how long it takes to access data stored in the database and how efficiently space in the database is used.

 

Appendix - Storage attributes

 

Physical attributes

Tablespace

A tablespace is an allocation of space in the database that can contain schema objects. Use the drop-down list to select the tablespace where the object will be stored.

 

Buffer pool

This option allows you to specify a default buffer pool or cache for the object. All blocks for the object are stored in the specified cache. Use the drop-down list to select one of the following values:

KEEP: the buffer pool retains the schema object's data blocks in memory;

RECYCLE: the buffer pool eliminates data blocks from memory as soon as they are no longer needed.

DEFAULT: the buffer pool contains data blocks from schema objects that are not assigned to any buffer pool, as well as schema objects that are explicitly assigned to the DEFAULT pool.

 

Initial number of transactions

Specify the initial number of concurrent transaction entries allocated within each data block allocated to the database object, or select DEFAULT from the drop-down list.

 

CheckBox Cache

Use this option to indicate how Oracle Database should store blocks in the buffer cache.

 

CheckBox Row dependencies

Select this option if you want to enable row-level dependency tracking. This setting is useful primarily to allow for parallel propagation in replication environments.

 

Extents

An extent is a logical unit of database storage space allocation made up of a number of contiguous data blocks. One or more extents in turn make up a segment. When the existing space in a segment is completely used, Oracle allocates a new extent for the segment.

 

Initial extent

Specify the size (in bytes) of the first extent of the object. Oracle allocates space for this extent when you create the schema object, or select DEFAULT from the drop-down list.

 

Next extent

Specify the size (in bytes) of the next extent to be allocated to the object, or select DEFAULT from the drop-down list.

 

Percent increase

Specify the percent by which the third and subsequent extents grow over the preceding extent, or select DEFAULT from the drop-down list (the default value is 50, meaning that each subsequent extent is 50 per cent larger than the preceding extent)

 

Minimum extents

Specify the total number of extents to allocate when the object is created, or select DEFAULT from the drop-down list. This parameter lets you allocate a large amount of space when you create an object, even if the space available is not contiguous.

 

Maximum extents

Specify the total number of extents, including the first, that Oracle can allocate for the object, or select DEFAULT or UNLIMITED from the drop-down list.

 

Space usage

Parameters of this group allow you to control the use of free space for inserts and updates to the rows in all the data blocks of a particular segment.

 

Percent free

This parameter sets the minimum percentage of a data block to be reserved as free space for possible updates to rows that already exist in that block. Specify a value, or select DEFAULT from the drop-down list.

 

Percent used

This parameter sets the minimum percentage of a block that can be used for row data plus overhead before new rows are added to the block. Specify a value, or select DEFAULT from the drop-down list.

 

Free lists

Free lists

Specify the number of free lists that can be contained in each free list group, or select DEFAULT from the drop-down list (the default and minimum value for this parameter is 1, meaning that each free list group contains one free list).

 

Groups

Specify the number of groups of free lists for the database object being created, or select DEFAULT from the drop-down list (the default and minimum value for this parameter is 1).

 

Parallel

Use this group to specify the degree of parallel access to the object.

RadioButton Default

RadioButton No parallel (serial execution)

RadioButton Parallel (parallelized execution)

 

Parallel options

Degree

Specify the degree of parallelism which is the number of parallel threads used in the parallel operation, or select DEFAULT from the drop-down list.

A degree of parallelism equals to the number of CPUs available on all participating Instances.

 

Data storage options

This group is only available for tables which store data.

 

CheckBox Compress data

Use this option to instruct the database whether to compress data segments to reduce disk and memory use (for heap-organized tables).

 

CheckBox Enable row movement

This option allows you to specify whether the database can move a table row. It is possible for a row to move, for example, during table compression or an update operation on partitioned data. Note that when a row is moved, the rowid is changed.

 

Compress for

Use this group to specify the table compression mode:

RadioButton All operations (Oracle Database attempts to compress data during all DML operations on the table)

RadioButton Direct load operation (Oracle Database attempts to compress data during direct-path INSERT operations when it is productive to do so)