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I am measuring database performance and am looking at p95 and p99 latency. My results are as follows.

Database A shows:

95thPercentileLatency(ms)   20
99thPercentileLatency(ms)   28

Database B shows:

95thPercentileLatency(ms)   1
99thPercentileLatency(ms)   3

I understand that the 99th percentile latency indicates that 99% of operations completed in under a given latency, so for database B 3

I am unsure of the significance of 1 system having a 99th and 95th percentile latency that are very close to each other, and another where they are much further apart. What does this mean?

JamesF
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    One of them has the 99th percentile at 3 times the value of the 95th percentile; the other has it at 40% above. The bigger question to me would be "why is the Database A so much slower than Database B", rather than worrying about the difference between 2 ms and 8 ms delay time. Also, is there a problem? If the requirement is that 99th percentile should be under 1 second, then both systems are performing admirably. If the requirement is that the 99th percentile should be under 10 ms, you have problems in A and not in B. – Jonathan Leffler Apr 16 '15 at 23:37

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