Amplification

Worked examples, recomputed

Every number the mechanisms quote for this relationship is recomputed from it, so none of them disagrees with it.

• one 200-byte row from a 4 KiB page → ≈ 20×
• 1 MB read for 200 bytes → 5,000×
• a 200-byte change in a 128 MB file → 640,000×
• an 8 KB full-page image for a 100-byte record → ≈ 80×
• 1 MB block for a 100-byte row → ≈ 10,000×
• 4 KB block → ≈ 40×
• 256 KB block for 100 bytes → ≈ 2,600×
• 256 KB for a 40-byte row → ≈ 6,400×
• 16 KB page for a 200-byte row → ≈ 80×
• moving a 1,000-node subtree in a closure table → 6,000 row changes, against 1

Where it appears

Each mechanism states it in its own names. The general symbol each name stands for is shown with it.

• Storage: Physical Organization

  What should sit next to what, given that I must decide at write time and find out at read time?

  $$\text{amplification}=\text{bytes touched}÷\text{bytes needed}$$

  Read it in place →