Cost Models (cont)
Since time cost is affected by many factors
- speed of i/o devices (fast/slow disk, SSD)
- load on machine
we do not consider time cost in our analyses.
For comparing methods, page cost is better
- identifies workload imposed by method
- BUT is clearly affected by buffering
Estimating costs with multiple concurrent ops and buffering is difficult!!
Addtional assumption: every page request leads to some i/o
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