Store Gateway: Dedup ExpandPostings requests using singleflight

CHANGELOG.md

@@ -21,6 +21,7 @@ We use *breaking :warning:* to mark changes that are not backward compatible (re
 ### Added
 - [#7105](https://github.com/thanos-io/thanos/pull/7105) Rule: add flag `--query.enable-x-functions` to allow usage of extended promql functions (xrate, xincrease, xdelta) in loaded rules
 - [#6867](https://github.com/thanos-io/thanos/pull/6867) Query UI: Tenant input box added to the Query UI, in order to be able to specify which tenant the query should use.
+- [#7171](https://github.com/thanos-io/thanos/pull/7171) Store Gateway: Dedup `ExpandPostings` requests using singleFlight.
 
 ### Changed
 

pkg/store/bucket.go

@@ -24,6 +24,7 @@ import (
 	"github.com/go-kit/log"
 	"github.com/go-kit/log/level"
 	"github.com/gogo/protobuf/types"
+	"github.com/golang/groupcache/singleflight"
 	"github.com/oklog/ulid"
 	"github.com/pkg/errors"
 	"github.com/prometheus/client_golang/prometheus"
@@ -1096,11 +1097,15 @@ func (b *blockSeriesClient) ExpandPostings(
 	matchers sortedMatchers,
 	seriesLimiter SeriesLimiter,
 ) error {
-	ps, err := b.indexr.ExpandedPostings(b.ctx, matchers, b.bytesLimiter, b.lazyExpandedPostingEnabled, b.lazyExpandedPostingSizeBytes, b.tenant)
+	matchersKey := storecache.LabelMatchersToString(matchers)
+	res, err := b.indexr.block.g.Do(matchersKey, func() (interface{}, error) {
+		return b.indexr.ExpandedPostings(b.ctx, matchers, b.bytesLimiter, b.lazyExpandedPostingEnabled, b.lazyExpandedPostingSizeBytes, b.tenant)
+	})
 	if err != nil {
 		return errors.Wrap(err, "expanded matching posting")
 	}
 
+	ps := res.(*lazyExpandedPostings)
 	if ps == nil || len(ps.postings) == 0 {
 		b.lazyPostings = emptyLazyPostings
 		return nil
@@ -2245,6 +2250,8 @@ type bucketBlock struct {
 
 	partitioner Partitioner
 
+	g singleflight.Group
+
 	// Block's labels used by block-level matchers to filter blocks to query. These are used to select blocks using
 	// request hints' BlockMatchers.
 	relabelLabels labels.Labels