[dataangel]

It could be noise in a benchmark that does IO, or has determinism problems.

[rfoo]

Here is the benchmark output from the post:

  news_app/ranges_and_joins/cached
     time:   [28.583 ms 29.001 ms 29.526 ms]
     thrpt:  [277.45 Kelem/s 282.48 Kelem/s 286.61 Kelem/s]

  news_app/ranges_and_joins/cached
     time:   [33.271 ms 33.836 ms 34.418 ms]
     thrpt:  [238.01 Kelem/s 242.11 Kelem/s 246.22 Kelem/s]

Given that 33.836/(1000/(242.11*1000)) ~= 8192, my understanding is the time reported here is how long it takes to do 8192 queries. Also it reports three metrics (should be min, median and max). All these means the benchmark harness did run the test for a lot of times and the 5 ms different is not random at all.