remove tilde from name values when indexing tags

[replay]

I'll wait for this PR to get merged before this can be merged: raintank/schema@80d1297

This is related to grafana/grafana#15261
And it is the implementation of graphite-project/graphite-web#2458

[woodsaj]

Why all the complexity in this function. Cant you just use strings.ReplaceAll(name, "~", "")?

[replay]

I definitely can, but since this is a function that may get called very often (potentially millions of times in one query) I wanted to keep it as efficient as possible. let me benchmark which version is more efficient

[replay]

Actually, the definition of what is valid has just changed, so this function will get updated anyway
graphite-project/carbon#858 (comment)

[replay]

I pushed a new version. I benchmarked it and compared it with an alternative version which is simpler by relying on strings:

func SanitizeNameAsTagValue(name string) (string, error) {
	if len(name) == 0 {
		return name, fmt.Errorf("Invalid name of length 0")
	}

	if name[0] != '~' {
		return name, nil
	}

	name = strings.TrimLeft(name, "~")

	if len(name) == 0 {
		return "", fmt.Errorf("Invalid name, requiring other characters than ~")
	}

	return name, nil
}

The first one is with the latest commit that I pushed (raintank/schema@f065be1) and the second is with the above simplified version:

replay@vbox:~/go/src/github.com/raintank/schema$ go test -run=none -bench=BenchmarkNameSanitized
goos: linux
goarch: amd64
pkg: github.com/raintank/schema
BenchmarkNameSanitizedAsTagValueWithValidValue-3        300000000                5.02 ns/op
BenchmarkNameSanitizedAsTagValueWithInvalidValue-3      200000000                6.10 ns/op
PASS
ok      github.com/raintank/schema      3.867s
replay@vbox:~/go/src/github.com/raintank/schema$ go test -run=none -bench=BenchmarkNameSanitized
goos: linux
goarch: amd64
pkg: github.com/raintank/schema
BenchmarkNameSanitizedAsTagValueWithValidValue-3        300000000                5.09 ns/op
BenchmarkNameSanitizedAsTagValueWithInvalidValue-3      20000000                84.8 ns/op
PASS
ok      github.com/raintank/schema      3.810s

[replay]

Actually, I don't think it makes sense for this method to have the potential to return errors, if the returned value is "" then the caller should just have to deal with it, i'll change that

[replay]

I changed it again so the method does not return errors and compared the latest version (raintank/schema@1adcebf) with a simpler version relying on strings. it's quite a difference:

replay@vbox:~/go/src/github.com/raintank/schema$ go test -run=none -bench=BenchmarkNameSanitized
goos: linux
goarch: amd64
pkg: github.com/raintank/schema
BenchmarkNameSanitizedAsTagValueWithValidValue-3        300000000                4.41 ns/op
BenchmarkNameSanitizedAsTagValueWithInvalidValue-3      300000000                5.74 ns/op
PASS
ok      github.com/raintank/schema      4.095s
replay@vbox:~/go/src/github.com/raintank/schema$ go test -run=none -bench=BenchmarkNameSanitized
goos: linux
goarch: amd64
pkg: github.com/raintank/schema
BenchmarkNameSanitizedAsTagValueWithValidValue-3        20000000                70.4 ns/op
BenchmarkNameSanitizedAsTagValueWithInvalidValue-3      20000000                82.0 ns/op
PASS
ok      github.com/raintank/schema      3.220s

[replay]

This should be ready to review now

[Dieterbe]

minor nits, lgtm