store: validate --block-sync-concurrency parameter

CHANGELOG.md

@@ -13,6 +13,7 @@ We use *breaking :warning:* to mark changes that are not backward compatible (re
 ### Fixed
 
 - [#4663](https://github.com/thanos-io/thanos/pull/4663) Fetcher: Fix discovered data races
+- [#4753](https://github.com/thanos-io/thanos/pull/4753) Store: valide block sync concurrency parameter
 
 ### Added
 

cmd/thanos/store.go

@@ -113,7 +113,7 @@ func (sc *storeConfig) registerFlag(cmd extkingpin.FlagClause) {
 	cmd.Flag("sync-block-duration", "Repeat interval for syncing the blocks between local and remote view.").
 		Default("3m").DurationVar(&sc.syncInterval)
 
-	cmd.Flag("block-sync-concurrency", "Number of goroutines to use when constructing index-cache.json blocks from object storage.").
+	cmd.Flag("block-sync-concurrency", "Number of goroutines to use when constructing index-cache.json blocks from object storage. Must be equal or greater than 1.").
 		Default("20").IntVar(&sc.blockSyncConcurrency)
 
 	cmd.Flag("block-meta-fetch-concurrency", "Number of goroutines to use when fetching block metadata from object storage.").

pkg/store/bucket.go

@@ -92,6 +92,12 @@ const (
 	// Labels for metrics.
 	labelEncode = "encode"
 	labelDecode = "decode"
+
+	minBlockSyncConcurrency = 1
+)
+
+var (
+	errBlockSyncConcurrencyNotValid = errors.New("the block sync concurrency must be equal or greater than 1.")
 )
 
 type bucketStoreMetrics struct {
@@ -298,6 +304,13 @@ type BucketStore struct {
 	enableSeriesResponseHints bool
 }
 
+func (b *BucketStore) validate() error {
+	if b.blockSyncConcurrency < minBlockSyncConcurrency {
+		return errBlockSyncConcurrencyNotValid
+	}
+	return nil
+}
+
 type noopCache struct{}
 
 func (noopCache) StorePostings(context.Context, ulid.ULID, labels.Label, []byte) {}
@@ -407,6 +420,10 @@ func NewBucketStore(
 	s.indexReaderPool = indexheader.NewReaderPool(s.logger, lazyIndexReaderEnabled, lazyIndexReaderIdleTimeout, indexReaderPoolMetrics)
 	s.metrics = newBucketStoreMetrics(s.reg) // TODO(metalmatze): Might be possible via Option too
 
+	if err := s.validate(); err != nil {
+		return nil, errors.Wrap(err, "validate config")
+	}
+
 	if err := os.MkdirAll(dir, 0750); err != nil {
 		return nil, errors.Wrap(err, "create dir")
 	}

pkg/store/bucket_test.go

@@ -556,6 +556,32 @@ func TestGapBasedPartitioner_Partition(t *testing.T) {
 	}
 }
 
+func TestBucketStoreConfig_validate(t *testing.T) {
+	tests := map[string]struct {
+		config   *BucketStore
+		expected error
+	}{
+		"should pass on valid config": {
+			config: &BucketStore{
+				blockSyncConcurrency: 1,
+			},
+			expected: nil,
+		},
+		"should fail on blockSyncConcurrency < 1": {
+			config: &BucketStore{
+				blockSyncConcurrency: 0,
+			},
+			expected: errBlockSyncConcurrencyNotValid,
+		},
+	}
+
+	for testName, testData := range tests {
+		t.Run(testName, func(t *testing.T) {
+			testutil.Equals(t, testData.expected, testData.config.validate())
+		})
+	}
+}
+
 func TestBucketStore_Info(t *testing.T) {
 	defer testutil.TolerantVerifyLeak(t)