fix store: handle invalid cache block dir (thanos-io#1505)

* fix store: handle invalid cache block dir

Signed-off-by: Martin Chodur <m.chodur@seznam.cz>

* CR: simplify empty store cache block validation logic

Signed-off-by: Martin Chodur <m.chodur@seznam.cz>

CHANGELOG.md

@@ -11,6 +11,10 @@ We use *breaking* word for marking changes that are not backward compatible (rel
 
 ## Unreleased
 
+### Fixed
+
+-[1505](https://github.com/thanos-io/thanos/pull/1505) Thanos store now removes invalid local cache blocks.
+
 ## v0.7.0 - 2019.09.02
 
 Accepted into CNCF:

pkg/store/bucket.go

@@ -1188,8 +1188,8 @@ func (b *bucketBlock) indexCacheFilename() string {
 }
 
 func loadMeta(ctx context.Context, logger log.Logger, bucket objstore.BucketReader, dir string, id ulid.ULID) (error, *metadata.Meta) {
-	// If we haven't seen the block before download the meta.json file.
-	if _, err := os.Stat(dir); os.IsNotExist(err) {
+	// If we haven't seen the block before or it is missing the meta.json, download it.
+	if _, err := os.Stat(path.Join(dir, block.MetaFilename)); os.IsNotExist(err) {
 		if err := os.MkdirAll(dir, 0777); err != nil {
 			return errors.Wrap(err, "create dir"), nil
 		}