Optimize zlabel usage for stringlabels

Using the ZLabelsToPromLabels hack is no longer free with stringlabels
because the in-memory format of the two types is different. Because of this,
using a stringlabels build in the Receiver can be more CPU intensive than
the normal build.

In order to allow for an efficient usage of stringlabels, this commit removes
`ZLabelsToPromLabels` calls in TSDBStore and ProxyStore. There is now a specialized
implementation of ZLabel conversion functions with a stringlabels build tag in order to
avoid panics, but long term we should get rid of these functions if possible.

Signed-off-by: Filip Petkovski <filip.petkovsky@gmail.com>

cmd/thanos/rule.go

@@ -726,7 +726,7 @@ func runRule(
 		infoOptions = append(
 			infoOptions,
 			info.WithLabelSetFunc(func() []labelpb.ZLabelSet {
-				return tsdbStore.LabelSet()
+				return labelpb.ZLabelSetsFromPromLabels(tsdbStore.LabelSet()...)
 			}),
 			info.WithStoreInfoFunc(func() (*infopb.StoreInfo, error) {
 				if httpProbe.IsReady() {

pkg/receive/multitsdb.go

@@ -5,7 +5,6 @@ package receive
 
 import (
 	"context"
-	"fmt"
 	"os"
 	"path"
 	"path/filepath"
@@ -217,7 +216,7 @@ func (l *localClient) Matches(matchers []*labels.Matcher) bool {
 }
 
 func (l *localClient) LabelSets() []labels.Labels {
-	return labelpb.ZLabelSetsToPromLabelSets(l.store.LabelSet()...)
+	return l.store.LabelSet()
 }
 
 func (l *localClient) TimeRange() (mint int64, maxt int64) {
@@ -233,19 +232,17 @@ func (l *localClient) TSDBInfos() []infopb.TSDBInfo {
 	mint, maxt := l.store.TimeRange()
 	return []infopb.TSDBInfo{
 		{
-			Labels:  labelsets[0],
+			Labels: labelpb.ZLabelSet{
+				Labels: labelpb.ZLabelsFromPromLabels(labelsets[0]),
+			},
 			MinTime: mint,
 			MaxTime: maxt,
 		},
 	}
 }
 
 func (l *localClient) String() string {
-	mint, maxt := l.store.TimeRange()
-	return fmt.Sprintf(
-		"LabelSets: %v MinTime: %d MaxTime: %d",
-		labelpb.PromLabelSetsToString(l.LabelSets()), mint, maxt,
-	)
+	return l.store.String()
 }
 
 func (l *localClient) Addr() (string, bool) {

pkg/receive/receive_test.go

@@ -16,7 +16,6 @@ import (
 
 	"github.com/thanos-io/thanos/pkg/block/metadata"
 	"github.com/thanos-io/thanos/pkg/store"
-	"github.com/thanos-io/thanos/pkg/store/labelpb"
 	"github.com/thanos-io/thanos/pkg/testutil/custom"
 )
 
@@ -835,7 +834,7 @@ func setupSetsOfExpectedAndActualStoreClientLabelSets(
 		testStore := store.TSDBStore{}
 		testStore.SetExtLset(expectedExternalLabelSets[i])
 
-		expectedClientLabelSets := labelpb.ZLabelSetsToPromLabelSets(testStore.LabelSet()...)
+		expectedClientLabelSets := testStore.LabelSet()
 		setOfExpectedClientLabelSets = append(setOfExpectedClientLabelSets, expectedClientLabelSets)
 
 		actualClientLabelSets := actualStoreClients[i].LabelSets()