Use a heap for Next for merges, and
pre-compute if there's many postings on the
unset path.
Add posting lookup benchmarks
Signed-off-by: Brian Brazil <brian.brazil@robustperception.io>
With 1M series:
Before:
BenchmarkHeadPostingForMatchers-8 1 3501996117 ns/op 61311520 B/op 78 allocs/op
After:
BenchmarkHeadPostingForMatchers-8 1 1403072952 ns/op 69261568 B/op 72 allocs/op
This works out as 3X faster, as the above time includes other things.
Signed-off-by: Brian Brazil <brian.brazil@robustperception.io>
Some benchmarks for HEAD and allocate the correct slice size in LabelValues , we already know what it'll be
This is ~15% time improvement, and ~25% allocation improvement:
```
benchmark old ns/op new ns/op delta
BenchmarkHeadPostingForMatchers-4 74452 63514 -14.69%
benchmark old allocs new allocs delta
BenchmarkHeadPostingForMatchers-4 20 13 -35.00%
benchmark old bytes new bytes delta
BenchmarkHeadPostingForMatchers-4 5425 3137 -42.18%
```
Signed-off-by: Thomas Jackson <jacksontj.89@gmail.com>
