fix(blooms): Do not fail requests when fetching metas from cache fails (

#12838)

The bloom shipper uses metas to resolve available blocks. Metas are fetched from cache, and if not available from object storage.
If fetching metas from cache fails, e.g. timeout, the request should not fail, but proceed as if no metas were available.

Signed-off-by: Christian Haudum <christian.haudum@gmail.com>

pkg/storage/chunk/cache/mock.go

@@ -13,16 +13,27 @@ type MockCache interface {
 	GetInternal() map[string][]byte
 	KeysRequested() int
 	GetKeys() []string
+	SetErr(error, error)
 }
 
 type mockCache struct {
 	numKeyUpdates int
 	keysRequested int
 	sync.Mutex
-	cache map[string][]byte
+	cache    map[string][]byte
+	storeErr error // optional error that is returned when calling Store()
+	fetchErr error // optional error that is returned when calling Fetch()
+}
+
+func (m *mockCache) SetErr(storeErr, fetchErr error) {
+	m.storeErr, m.fetchErr = storeErr, fetchErr
 }
 
 func (m *mockCache) Store(_ context.Context, keys []string, bufs [][]byte) error {
+	if m.storeErr != nil {
+		return m.storeErr
+	}
+
 	m.Lock()
 	defer m.Unlock()
 	for i := range keys {
@@ -33,6 +44,10 @@ func (m *mockCache) Store(_ context.Context, keys []string, bufs [][]byte) error
 }
 
 func (m *mockCache) Fetch(_ context.Context, keys []string) (found []string, bufs [][]byte, missing []string, err error) {
+	if m.fetchErr != nil {
+		return nil, nil, nil, m.fetchErr
+	}
+
 	m.Lock()
 	defer m.Unlock()
 	for _, key := range keys {

pkg/storage/stores/shipper/bloomshipper/fetcher.go

@@ -129,7 +129,8 @@ func (f *Fetcher) FetchMetas(ctx context.Context, refs []MetaRef) ([]Meta, error
 	}
 	cacheHits, cacheBufs, _, err := f.metasCache.Fetch(ctx, keys)
 	if err != nil {
-		return nil, err
+		level.Error(f.logger).Log("msg", "failed to fetch metas from cache", "err", err)
+		return nil, nil
 	}
 
 	fromCache, missing, err := f.processMetasCacheResponse(ctx, refs, cacheHits, cacheBufs)

pkg/storage/stores/shipper/bloomshipper/fetcher_test.go

@@ -11,6 +11,7 @@ import (
 	"time"
 
 	"github.com/go-kit/log"
+	"github.com/pkg/errors"
 	"github.com/prometheus/common/model"
 	"github.com/stretchr/testify/require"
 
@@ -72,6 +73,7 @@ func TestMetasFetcher(t *testing.T) {
 		start []Meta // initial cache state
 		end   []Meta // final cache state
 		fetch []Meta // metas to fetch
+		err   error  // error that is returned when calling cache.Fetch()
 	}{
 		{
 			name:  "all metas found in cache",
@@ -94,12 +96,22 @@ func TestMetasFetcher(t *testing.T) {
 			end:   makeMetas(t, schemaCfg, now, []v1.FingerprintBounds{{Min: 0x0000, Max: 0xffff}, {Min: 0x10000, Max: 0x1ffff}}),
 			fetch: makeMetas(t, schemaCfg, now, []v1.FingerprintBounds{{Min: 0x0000, Max: 0xffff}, {Min: 0x10000, Max: 0x1ffff}}),
 		},
+		{
+			name:  "error fetching metas yields empty result",
+			err:   errors.New("failed to fetch"),
+			store: makeMetas(t, schemaCfg, now, []v1.FingerprintBounds{{Min: 0x0000, Max: 0xffff}, {Min: 0x10000, Max: 0x1ffff}}),
+			start: makeMetas(t, schemaCfg, now, []v1.FingerprintBounds{{Min: 0x0000, Max: 0xffff}}),
+			end:   makeMetas(t, schemaCfg, now, []v1.FingerprintBounds{{Min: 0x0000, Max: 0xffff}}),
+			fetch: []Meta{},
+		},
 	}
 
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
 			ctx := context.Background()
 			metasCache := cache.NewMockCache()
+			metasCache.SetErr(nil, test.err)
+
 			cfg := bloomStoreConfig{workingDirs: []string{t.TempDir()}, numWorkers: 1}
 
 			oc, err := local.NewFSObjectClient(local.FSConfig{Directory: dir})