ingester: reduce activity tracker memory allocation

[ortuman]

Signed-off-by: Miguel Ángel Ortuño ortuman@gmail.com

What this PR does

Added custom stringer for *client.QueryRequest to minimize memory allocation on ingester activity tracker record generator.

old:

BenchmarkRequestActivity-8   	 1284216	       927.5 ns/op	     984 B/op	      21 allocs/op
BenchmarkRequestActivity-8   	 1291141	       928.1 ns/op	     984 B/op	      21 allocs/op
BenchmarkRequestActivity-8   	 1289739	       928.9 ns/op	     984 B/op	      21 allocs/op
BenchmarkRequestActivity-8   	 1287590	       927.4 ns/op	     984 B/op	      21 allocs/op
BenchmarkRequestActivity-8   	 1287128	       934.3 ns/op	     984 B/op	      21 allocs/op
BenchmarkRequestActivity-8   	 1294728	       931.9 ns/op	     984 B/op	      21 allocs/op
BenchmarkRequestActivity-8   	 1291026	       928.1 ns/op	     984 B/op	      21 allocs/op
BenchmarkRequestActivity-8   	 1289536	       931.1 ns/op	     984 B/op	      21 allocs/op
BenchmarkRequestActivity-8   	 1289566	       933.2 ns/op	     984 B/op	      21 allocs/op
BenchmarkRequestActivity-8   	 1289500	       929.1 ns/op	     984 B/op	      21 allocs/op

new:

BenchmarkRequestActivity-8   	 3293625	       355.1 ns/op	     224 B/op	       1 allocs/op
BenchmarkRequestActivity-8   	 3372951	       356.3 ns/op	     224 B/op	       1 allocs/op
BenchmarkRequestActivity-8   	 3375446	       355.1 ns/op	     224 B/op	       1 allocs/op
BenchmarkRequestActivity-8   	 3357924	       356.0 ns/op	     224 B/op	       1 allocs/op
BenchmarkRequestActivity-8   	 3372872	       355.6 ns/op	     224 B/op	       1 allocs/op
BenchmarkRequestActivity-8   	 3371698	       355.7 ns/op	     224 B/op	       1 allocs/op
BenchmarkRequestActivity-8   	 3369746	       355.9 ns/op	     224 B/op	       1 allocs/op
BenchmarkRequestActivity-8   	 3374049	       355.5 ns/op	     224 B/op	       1 allocs/op
BenchmarkRequestActivity-8   	 3373887	       356.5 ns/op	     224 B/op	       1 allocs/op
BenchmarkRequestActivity-8   	 3376087	       355.4 ns/op	     224 B/op	       1 allocs/op

comparison:

name               old time/op    new time/op    delta
RequestActivity-8     930ns ± 0%     356ns ± 0%  -61.75%  (p=0.000 n=10+10)

name               old alloc/op   new alloc/op   delta
RequestActivity-8      984B ± 0%      224B ± 0%  -77.24%  (p=0.000 n=10+10)

name               old allocs/op  new allocs/op  delta
RequestActivity-8      21.0 ± 0%       1.0 ± 0%  -95.24%  (p=0.000 n=10+10)

Which issue(s) this PR fixes or relates to

Fixes #3192

Checklist

• Tests updated
• Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

[pstibrany]

Looking at the benchmark, and original issue #3192, I am not sure we're spending time well by optimizing this. It's a lot of extra code (although easy to follow) for tiny benefit in my opinion.