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Storage Structure and Relationships
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Database Storage Hierarchy
Tablespace Data file Logical Segment Physical Extent Oracle block O/S block
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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
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Database Block Contents
Header Free space Data
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Block Space Utilization Parameters
INITRANS MAXTRANS PCTFREE PCTUSED
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Block Space Usage Inserts Inserts 1 2 Inserts Inserts 3 4
PCTFREE= PCTUSED=40 Inserts Inserts 80% 1 2 Inserts 80% Inserts 40% 3 4
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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
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Summary Allocation and deallocation of extents for different types of segments Block space utilization parameters
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