Storage Structure and Relationships

Database Storage Hierarchy Tablespace Data file Logical Segment Physical Extent Oracle block O/S block

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

Database Block Contents Header Free space Data

Block Space Utilization Parameters INITRANS MAXTRANS PCTFREE PCTUSED

Block Space Usage Inserts Inserts 1 2 Inserts Inserts 3 4 PCTFREE=20 PCTUSED=40 Inserts Inserts 80% 1 2 Inserts 80% Inserts 40% 3 4

Organizing Tablespaces Based on Fragmentation Propensity SYSTEM TOOLS DATAn INDEXn RBSn TEMPn Usage Data dictionary Applications Data segments Index segments Rollback segments Temporary segments Fragmentation Zero Very low Low High Very high* * Relevant only if tablespace PERMANENT

Summary Allocation and deallocation of extents for different types of segments Block space utilization parameters