Add tracing index cache (#6954)

* add tracing index cache

Signed-off-by: Ben Ye <benye@amazon.com>

* changelog

Signed-off-by: Ben Ye <benye@amazon.com>

---------

Signed-off-by: Ben Ye <benye@amazon.com>

CHANGELOG.md

@@ -19,6 +19,7 @@ We use *breaking :warning:* to mark changes that are not backward compatible (re
 - [#6891](https://github.com/thanos-io/thanos/pull/6891) Objstore: Bump `objstore` which adds support for Azure Workload Identity.
 - [#6453](https://github.com/thanos-io/thanos/pull/6453) Sidecar: Added `--reloader.method` to support configuration reloads via SIHUP signal.
 - [#6925](https://github.com/thanos-io/thanos/pull/6925) Store Gateway: Support float native histogram.
+- [#6954](https://github.com/thanos-io/thanos/pull/6954) Index Cache: Support tracing for fetch APIs.
 
 ### Changed
 

pkg/store/cache/factory.go

@@ -78,6 +78,7 @@ func NewIndexCache(logger log.Logger, confContentYaml []byte, reg prometheus.Reg
 		return nil, errors.Wrap(err, fmt.Sprintf("create %s index cache", cacheConfig.Type))
 	}
 
+	cache = NewTracingIndexCache(string(cacheConfig.Type), cache)
 	if len(cacheConfig.EnabledItems) > 0 {
 		if err = ValidateEnabledItems(cacheConfig.EnabledItems); err != nil {
 			return nil, err

pkg/store/cache/tracing_index_cache.go

@@ -0,0 +1,92 @@
+// Copyright (c) The Thanos Authors.
+// Licensed under the Apache License 2.0.
+
+package storecache
+
+import (
+	"context"
+
+	"github.com/oklog/ulid"
+	"github.com/prometheus/prometheus/model/labels"
+	"github.com/prometheus/prometheus/storage"
+
+	"github.com/thanos-io/thanos/pkg/tracing"
+)
+
+type TracingIndexCache struct {
+	name  string
+	cache IndexCache
+}
+
+// NewTracingIndexCache creates an index cache wrapper with traces instrumentation.
+func NewTracingIndexCache(name string, cache IndexCache) *TracingIndexCache {
+	return &TracingIndexCache{name: name, cache: cache}
+}
+
+// StorePostings stores postings for a single series.
+func (c *TracingIndexCache) StorePostings(blockID ulid.ULID, l labels.Label, v []byte, tenant string) {
+	c.cache.StorePostings(blockID, l, v, tenant)
+}
+
+// FetchMultiPostings fetches multiple postings - each identified by a label -
+// and returns a map containing cache hits, along with a list of missing keys.
+func (c *TracingIndexCache) FetchMultiPostings(ctx context.Context, blockID ulid.ULID, keys []labels.Label, tenant string) (hits map[labels.Label][]byte, misses []labels.Label) {
+	span, newCtx := tracing.StartSpan(ctx, "fetch_multi_postings", tracing.Tags{
+		"name":      c.name,
+		"block.id":  blockID.String(),
+		"requested": len(keys),
+	})
+	defer span.Finish()
+	hits, misses = c.cache.FetchMultiPostings(newCtx, blockID, keys, tenant)
+	span.SetTag("hits", len(hits))
+	dataBytes := 0
+	for _, v := range hits {
+		dataBytes += len(v)
+	}
+	span.SetTag("bytes", dataBytes)
+	return hits, misses
+}
+
+// StoreExpandedPostings stores expanded postings for a set of label matchers.
+func (c *TracingIndexCache) StoreExpandedPostings(blockID ulid.ULID, matchers []*labels.Matcher, v []byte, tenant string) {
+	c.cache.StoreExpandedPostings(blockID, matchers, v, tenant)
+}
+
+// FetchExpandedPostings fetches expanded postings and returns cached data and a boolean value representing whether it is a cache hit or not.
+func (c *TracingIndexCache) FetchExpandedPostings(ctx context.Context, blockID ulid.ULID, matchers []*labels.Matcher, tenant string) (data []byte, exists bool) {
+	span, newCtx := tracing.StartSpan(ctx, "fetch_expanded_postings", tracing.Tags{
+		"name":     c.name,
+		"block.id": blockID.String(),
+	})
+	defer span.Finish()
+	data, exists = c.cache.FetchExpandedPostings(newCtx, blockID, matchers, tenant)
+	if exists {
+		span.SetTag("bytes", len(data))
+	}
+	return data, exists
+}
+
+// StoreSeries stores a single series. Skip intrumenting this method
+// excessive spans as a single request can store millions of serieses.
+func (c *TracingIndexCache) StoreSeries(blockID ulid.ULID, id storage.SeriesRef, v []byte, tenant string) {
+	c.cache.StoreSeries(blockID, id, v, tenant)
+}
+
+// FetchMultiSeries fetches multiple series - each identified by ID - from the cache
+// and returns a map containing cache hits, along with a list of missing IDs.
+func (c *TracingIndexCache) FetchMultiSeries(ctx context.Context, blockID ulid.ULID, ids []storage.SeriesRef, tenant string) (hits map[storage.SeriesRef][]byte, misses []storage.SeriesRef) {
+	span, newCtx := tracing.StartSpan(ctx, "fetch_multi_series", tracing.Tags{
+		"name":      c.name,
+		"block.id":  blockID.String(),
+		"requested": len(ids),
+	})
+	defer span.Finish()
+	hits, misses = c.cache.FetchMultiSeries(newCtx, blockID, ids, tenant)
+	span.SetTag("hits", len(hits))
+	dataBytes := 0
+	for _, v := range hits {
+		dataBytes += len(v)
+	}
+	span.SetTag("bytes", dataBytes)
+	return hits, misses
+}