8-Storage Structure

Segments tracking in segment free and used space is

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Unformatted text preview: CTUSED, FREELISTS are managed automatically – Ease of use • It is a method of managing free space inside database segments • Tracking in-segment free and used space is done using bitmaps as opposed to free lists • This method provides Automatic Segment-Space Management Storage Structure Tathagata Bhattacharjee • Run-time adjustments to variations in concurrent access are improved • Restrictions: Can not be used for tablespaces which will contain LOBs Storage Structure Tathagata Bhattacharjee • Bitmap segments contain a bitmap that describes the status of each block in the segment with respect to its available space • The map is contained in a separate set of blocks referred to as bitmapped blocks (BMBs) • When inserting a new row, the server searches the map for a block with sufficient space • As the amount of space available in a block changes, its new state is reflected in the bitmap Storage Structure Tathagata Bhattacharjee SQL> CREATE TABLESPACE data02 DATAFILE ‘d:\oracle\oradata\mydb\data02.dbf’ SIZE 5M EXTENT MANAGEMENT LOCAL UNIFORM SIZE 64K SEGMENT SPACE MANAGEMENT AUTO; • Automatic segment-space management can be enabled at the tablespace level only, for locally managed tablespaces • After a tablespace is created, the specifications apply to all segments created in the tablespace Configuring Automatic SegmentSpace Management Storage Structure Tathagata Bhattacharjee • Only method available in previous Oracle versions – PCTFREE PCTUSED FREELIST • Allows you to configure data blocks manually using parameters such as: Manual Data Block Management 1. Rows are inserted into blocks until the free space in the block is equal to or less than 20%. The block is no longer available for inserts when rows occupy 80% or more of the available data space in the block 2. The remaining 20% can be used when the size of a row increases. E.g. a column that was originally NULL is updated to an a value. Thus block utilization may be in access Tathagata Bhattacharjeea of 80% as Storage Structure result of updates • The following steps explain how...
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