intermediate~2h
Physical Storage: Blocks, Extents & Segments
How a table's rows actually end up laid out on disk — the block, extent, and segment hierarchy that underlies every I/O decision an optimizer ever makes.
Learning objectives
- Describe the block → extent → segment storage hierarchy and what each level actually represents
- Explain how rows are packed into a data block and why block size is a tuning lever
- Explain why a table's physical layout on disk directly affects how many blocks a query must touch
- Reason about row chaining, migration, and PCTFREE and how they create avoidable I/O
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Physical Storage: Blocks, Extents & Segments