Cache aside

What happens when the hit rate falls

The cache absorbs most reads. Lower the hit rate and the database takes the whole load.

What to watch

The database only ever sees the misses. At an 85 percent hit rate it takes about 30 requests a second out of 200. Drag the hit rate down to 0.3 and it is instantly over its 133 a second ceiling, with no change in load at all.

What it is made of

Component	Count
Cache	1
Client	1
Database	1
Service	1

Under load

Measured by running this design through the simulator at multiples of its own offered rate of 200 requests a second. Twenty seconds of simulated time, one fixed seed, so the same numbers come out every time.

This design holds 800 requests a second with 0% errors. At 1200 it is losing 3% of them.

Offered	Goodput	p99	Errors
200	204	61.9ms	0%
300	302	73.9ms	0%
400	417	80.3ms	0%
500	522	108.6ms	0%
600	633	95.6ms	0%
800	820	143.6ms	0%
1200	1066	313.8ms	3.2%
1600	1520	320.7ms	8.1%

Open this example

Load Cache aside from the Examples menu and drag the traffic slider yourself.