Model
Block nested loop I/O
The chunk size is memory, and the fixed cost being shared is a full pass over S.
- Inputs
- pages of the outer and inner input
- Memory
- pages of the outer held per chunk
How it behaves
One input on the horizontal axis, the others held fixed.
Data table
| Memory M (pages) | Page reads |
|---|---|
| 10 | 1M |
| 10.7 | 941K |
| 11.4 | 881K |
| 12.2 | 821K |
| 13 | 771K |
| 13.9 | 721K |
| 14.9 | 681K |
| 15.9 | 631K |
| 17 | 591K |
| 18.1 | 561K |
| 19.4 | 521K |
| 20.7 | 491K |
| 22.1 | 461K |
| 23.7 | 431K |
| 25.3 | 401K |
| 27 | 381K |
| 28.9 | 351K |
| 30.8 | 331K |
| 32.9 | 311K |
| 35.2 | 291K |
| 37.6 | 271K |
| 40.2 | 251K |
| 42.9 | 241K |
| 45.9 | 221K |
| 49 | 211K |
| 52.4 | 201K |
| 56 | 181K |
| 59.8 | 171K |
| 63.9 | 161K |
| 68.3 | 151K |
| 72.9 | 141K |
| 77.9 | 131K |
| 83.3 | 131K |
| 89 | 121K |
| 95 | 111K |
| 102 | 101K |
| 109 | 101K |
| 116 | 91K |
| 124 | 91K |
| 132 | 81K |
| 141 | 81K |
| 151 | 71K |
| 161 | 71K |
| 173 | 61K |
| 184 | 61K |
| 197 | 61K |
| 210 | 51K |
| 225 | 51K |
| 240 | 51K |
| 257 | 41K |
| 274 | 41K |
| 293 | 41K |
| 313 | 41K |
| 335 | 31K |
| 357 | 31K |
| 382 | 31K |
| 408 | 31K |
| 436 | 31K |
| 466 | 31K |
| 498 | 31K |
| 532 | 21K |
| 568 | 21K |
| 607 | 21K |
| 649 | 21K |
| 693 | 21K |
| 741 | 21K |
| 791 | 21K |
| 845 | 21K |
| 903 | 21K |
| 965 | 21K |
| 1.03K | 11K |
| 1.1K | 11K |
| 1.18K | 11K |
| 1.26K | 11K |
| 1.34K | 11K |
| 1.44K | 11K |
| 1.53K | 11K |
| 1.64K | 11K |
| 1.75K | 11K |
| 1.87K | 11K |
| 2K | 11K |
Worked examples, recomputed
Every number the mechanisms quote for this relationship is recomputed from it, so none of them disagrees with it.
Where it appears
Each mechanism states it in its own names. The general symbol each name stands for is shown with it.
- Query Processing
Why can one question be answered by plans whose costs differ by a factor of ten thousand, and what does each operator force the engine to do?