Handle not found metas gracefully

There is a time window between between listing metas and fetching them
from object storage which could lead to a race condition that the meta
is not found in object storage, because it was deleted and superseded by
a newer meta.

This can happen when querying recent bloom data, that is still subject
to updates.

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

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

@@ -12,6 +12,7 @@ import (
 	"time"
 
 	"github.com/go-kit/log"
+	"github.com/go-kit/log/level"
 	"github.com/grafana/dskit/concurrency"
 	"github.com/pkg/errors"
 	"github.com/prometheus/common/model"
@@ -385,31 +386,33 @@ func (b *BloomClient) Stop() {
 
 func (b *BloomClient) GetMetas(ctx context.Context, refs []MetaRef) ([]Meta, error) {
 	results := make([]Meta, len(refs))
-	err := concurrency.ForEachJob(ctx, len(refs), b.concurrency, func(ctx context.Context, idx int) error {
+	_ = concurrency.ForEachJob(ctx, len(refs), b.concurrency, func(ctx context.Context, idx int) error {
 		meta, err := b.GetMeta(ctx, refs[idx])
 		if err != nil {
-			return err
+			level.Error(b.logger).Log("msg", "failed to get meta", "err", err)
 		}
 		results[idx] = meta
 		return nil
 	})
-	return results, err
+	return results, nil
 }
 
+// GetMeta fetches the meta file for given MetaRef from object storage and
+// decodes the JSON data into a Meta.
+// If the meta file is not found in storage or decoding fails, the empty Meta
+// is returned along with the error.
 func (b *BloomClient) GetMeta(ctx context.Context, ref MetaRef) (Meta, error) {
-	meta := Meta{
-		MetaRef: ref,
-	}
+	meta := Meta{MetaRef: ref}
 	key := b.KeyResolver.Meta(ref).Addr()
 	reader, _, err := b.client.GetObject(ctx, key)
 	if err != nil {
-		return Meta{}, fmt.Errorf("failed to get meta file%s: %w", key, err)
+		return meta, fmt.Errorf("failed to fetch meta file %s: %w", key, err)
 	}
 	defer reader.Close()
 
 	err = json.NewDecoder(reader).Decode(&meta)
 	if err != nil {
-		return Meta{}, fmt.Errorf("failed to decode meta file %s: %w", key, err)
+		return meta, fmt.Errorf("failed to decode meta file %s: %w", key, err)
 	}
 	return meta, nil
 }

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

@@ -107,11 +107,20 @@ func TestBloomClient_GetMetas(t *testing.T) {
 		require.Equal(t, metas, []Meta{m1, m2})
 	})
 
-	t.Run("does not exist", func(t *testing.T) {
-		metas, err := c.GetMetas(ctx, []MetaRef{{}})
-		require.Error(t, err)
-		require.True(t, c.client.IsObjectNotFoundErr(err))
-		require.Equal(t, metas, []Meta{{}})
+	t.Run("does not exist - yields empty meta", func(t *testing.T) {
+		ref := MetaRef{
+			Ref: Ref{
+				TenantID:       "tenant",
+				TableName:      "table",
+				Bounds:         v1.FingerprintBounds{},
+				StartTimestamp: 1000,
+				EndTimestamp:   2000,
+				Checksum:       1234,
+			},
+		}
+		metas, err := c.GetMetas(ctx, []MetaRef{ref})
+		require.NoError(t, err)
+		require.Equal(t, metas, []Meta{{MetaRef: ref}})
 	})
 }