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6579dc3e40
The first sort in groupByFingerprint already ensures that all resulting sample lists contain only one fingerprint. We also already assume that all samples passed into AppendSamples (and thus groupByFingerprint) are chronologically sorted within each fingerprint. The extra chronological sort is thus superfluous. Furthermore, this second sort didn't only sort chronologically, but also compared all metric fingerprints again (although we already know that we're only sorting within samples for the same fingerprint). This caused a huge memory and runtime overhead. In a heavily loaded real Prometheus, this brought down disk flush times from ~9 minutes to ~1 minute. OLD: BenchmarkLevelDBAppendRepeatingValues 5 331391808 ns/op 44542953 B/op 597788 allocs/op BenchmarkLevelDBAppendsRepeatingValues 5 329893512 ns/op 46968288 B/op 3104373 allocs/op NEW: BenchmarkLevelDBAppendRepeatingValues 5 299298635 ns/op 43329497 B/op 567616 allocs/op BenchmarkLevelDBAppendsRepeatingValues 20 92204601 ns/op 1779454 B/op 70975 allocs/op Change-Id: Ie2d8db3569b0102a18010f9e106e391fda7f7883