Tham khảo tài liệu 'oracle 8 database administration volume 1 instruction guide phần 8', công nghệ thông tin, cơ sở dữ liệu phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Types of Segments Coalescing on Demand The view DBA_FREE_SPACE_COALESCED can be used to find out if any tablespace has extents that can be coalesced. Use the following query to get this information SVRMGR SELECT tablespace_name total_extents 2 percent_extents_coalesced 3 FROM dba_free_space_coalesced 4 WHERE percent_extents_coalesced 100 TABLESPACE_NAME TOTAL_EXTE PERCENT_EX RBS 3 33 DATA01 9 22 2 rows selected. Coalescing free space in a tablespace can be performed by executing the command ALTER TABLESPACE tablespace COALESCE OEM 1 Use Oracle Tablespace Manager. 2 Expand Tablespaces node. 3 Select the tablespace. 4 Select Tools Coalesce Free Extents. Oracle8 Database Administration 9-15 Lesson 9 Storage Structure and Relationships Using Block Space Utilization Parameters Database Block Review Minimum unit of I O Consists of one or more O S blocks Set by DB_BLOCK_SIZE Set at database creation 9-11 Copyright Oracle Corporation 1998. All rights reserved. ORACLE 9-16 Oracle8 Database Administration Using Block Space Utilization Parameters Oracle data blocks contain Block header Header contains the data block address table directory row directory and transaction slots that are used when transactions make changes to rows in the block. Block headers grow from the top down. Data space Row data is inserted into the block bottom up. Free space The free space in a block is in the middle allowing both the header and the row data space to grow if necessary. The free space in a block is contiguous initially. However deletions and updates may fragment the free space in the block. The free space in the block is coalesced by the Oracle server when necessary. Oracle8 Database Administration .
