Cache Hit Rate Backend Load Calculator

Method, formula and assumptions

Origin request rate = total request rate x miss fraction. Mean response is the hit/miss weighted mean. Capacity use divides origin requests by entered measured origin capacity.

Input definitions and supported units

• Incoming requests per second: Measured or assumed numerical value, from 0 to 100000000; zero is supported where the stated method permits it.
• Cache hit rate (%): Measured or assumed numerical value, from 0 to 100; zero is supported where the stated method permits it.
• Mean cache-hit time (ms): Measured or assumed numerical value, from 0 to 1000000; zero is supported where the stated method permits it.
• Mean cache-miss time (ms): Measured or assumed numerical value, from 0 to 1000000; zero is supported where the stated method permits it.
• Measured origin capacity (requests/s): Measured or assumed numerical value, from 0.001 to 100000000; must be positive.

Worked example with answer

1,000 requests/s at 90% hits leaves 100 origin requests/s. Hit time 2 ms and miss time 100 ms yield 11.8 ms mean, 50% use of a 200 requests/s origin and 100 requests/s margin.

How to use the results

The mean is not a percentile. Negative capacity margin indicates excess average demand before considering bursts or cache warm-up.

Results retain full precision internally and display up to four decimal places. Very small nonzero results use scientific notation rather than appearing as zero. Check the labels before comparing values across units.

Limitations and references

Assumes misses each create one origin request and no coalescing. Stampedes, stale refresh, cache lookups on miss and different object sizes require more detailed measurements.

The method is a self-contained arithmetic, geometric or explicitly stated mathematical model. There are no imported tariffs, empirical presets or equipment specifications; measured values and allowances must come from your own process.

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