Simplify mergedPostings.Seek (#595)
The current implementation leads to very slow behaviour when there's
many lists, this no worse than n log k, where k is the number of posting
lists.
Adjust benchmark to catch this.
Remove flattening of without lists, not needed anymore.
Benchmark versus 0.4.0 (used in Prometheus 2.7):
```
benchmark old ns/op new ns/op delta
BenchmarkHeadPostingForMatchers/n="1"-8 189907976 188863880 -0.55%
BenchmarkHeadPostingForMatchers/n="1",j="foo"-8 113950106 110791414 -2.77%
BenchmarkHeadPostingForMatchers/j="foo",n="1"-8 104965646 102388760 -2.45%
BenchmarkHeadPostingForMatchers/n="1",j!="foo"-8 138743592 104424250 -24.74%
BenchmarkHeadPostingForMatchers/i=~".*"-8 5279594954 5206096267 -1.39%
BenchmarkHeadPostingForMatchers/i=~".+"-8 8004610589 6184527719 -22.74%
BenchmarkHeadPostingForMatchers/i=~""-8 2476042646 1003920432 -59.45%
BenchmarkHeadPostingForMatchers/i!=""-8 7178244655 6059725323 -15.58%
BenchmarkHeadPostingForMatchers/n="1",i=~".*",j="foo"-8 199342649 166642946 -16.40%
BenchmarkHeadPostingForMatchers/n="1",i=~".*",i!="2",j="foo"-8 215774683 167515095 -22.37%
BenchmarkHeadPostingForMatchers/n="1",i!=""-8 2214714769 392943663 -82.26%
BenchmarkHeadPostingForMatchers/n="1",i!="",j="foo"-8 2148727410 322289262 -85.00%
BenchmarkHeadPostingForMatchers/n="1",i=~".+",j="foo"-8 2170658009 338458171 -84.41%
BenchmarkHeadPostingForMatchers/n="1",i=~"1.+",j="foo"-8 235720135 70597905 -70.05%
BenchmarkHeadPostingForMatchers/n="1",i=~".+",i!="2",j="foo"-8 2190570590 343034307 -84.34%
BenchmarkHeadPostingForMatchers/n="1",i=~".+",i!~"2.*",j="foo"-8 2373784439 387297908 -83.68%
benchmark old allocs new allocs delta
BenchmarkHeadPostingForMatchers/n="1"-8 33 33 +0.00%
BenchmarkHeadPostingForMatchers/n="1",j="foo"-8 33 33 +0.00%
BenchmarkHeadPostingForMatchers/j="foo",n="1"-8 33 33 +0.00%
BenchmarkHeadPostingForMatchers/n="1",j!="foo"-8 41 39 -4.88%
BenchmarkHeadPostingForMatchers/i=~".*"-8 56 56 +0.00%
BenchmarkHeadPostingForMatchers/i=~".+"-8 251577 100115 -60.21%
BenchmarkHeadPostingForMatchers/i=~""-8 251123 100077 -60.15%
BenchmarkHeadPostingForMatchers/i!=""-8 251525 100112 -60.20%
BenchmarkHeadPostingForMatchers/n="1",i=~".*",j="foo"-8 42 39 -7.14%
BenchmarkHeadPostingForMatchers/n="1",i=~".*",i!="2",j="foo"-8 52 42 -19.23%
BenchmarkHeadPostingForMatchers/n="1",i!=""-8 251069 100101 -60.13%
BenchmarkHeadPostingForMatchers/n="1",i!="",j="foo"-8 251473 100101 -60.19%
BenchmarkHeadPostingForMatchers/n="1",i=~".+",j="foo"-8 250914 100102 -60.11%
BenchmarkHeadPostingForMatchers/n="1",i=~"1.+",j="foo"-8 30038 11181 -62.78%
BenchmarkHeadPostingForMatchers/n="1",i=~".+",i!="2",j="foo"-8 250813 100105 -60.09%
BenchmarkHeadPostingForMatchers/n="1",i=~".+",i!~"2.*",j="foo"-8 281503 111260 -60.48%
benchmark old bytes new bytes delta
BenchmarkHeadPostingForMatchers/n="1"-8 10887600 10887600 +0.00%
BenchmarkHeadPostingForMatchers/n="1",j="foo"-8 5456416 5456416 +0.00%
BenchmarkHeadPostingForMatchers/j="foo",n="1"-8 5456416 5456416 +0.00%
BenchmarkHeadPostingForMatchers/n="1",j!="foo"-8 5456640 5456544 -0.00%
BenchmarkHeadPostingForMatchers/i=~".*"-8 258254504 258254472 -0.00%
BenchmarkHeadPostingForMatchers/i=~".+"-8 520126192 281554792 -45.87%
BenchmarkHeadPostingForMatchers/i=~""-8 263446640 24908456 -90.55%
BenchmarkHeadPostingForMatchers/i!=""-8 520121144 281553664 -45.87%
BenchmarkHeadPostingForMatchers/n="1",i=~".*",j="foo"-8 7062448 7062272 -0.00%
BenchmarkHeadPostingForMatchers/n="1",i=~".*",i!="2",j="foo"-8 7063473 7062384 -0.02%
BenchmarkHeadPostingForMatchers/n="1",i!=""-8 274325656 35793776 -86.95%
BenchmarkHeadPostingForMatchers/n="1",i!="",j="foo"-8 268926824 30362624 -88.71%
BenchmarkHeadPostingForMatchers/n="1",i=~".+",j="foo"-8 268882992 30363000 -88.71%
BenchmarkHeadPostingForMatchers/n="1",i=~"1.+",j="foo"-8 33193401 4269304 -87.14%
BenchmarkHeadPostingForMatchers/n="1",i=~".+",i!="2",j="foo"-8 268875024 30363096 -88.71%
BenchmarkHeadPostingForMatchers/n="1",i=~".+",i!~"2.*",j="foo"-8 300589656 33099784 -88.99%
```
Signed-off-by: Brian Brazil <brian.brazil@robustperception.io>
89a90fe96c