concurrently load bucket metadata (minio#9749)

cmd/bucket-metadata-sys.go

@@ -30,6 +30,7 @@ import (
 	"github.com/minio/minio/pkg/bucket/policy"
 	"github.com/minio/minio/pkg/event"
 	"github.com/minio/minio/pkg/madmin"
+	"github.com/minio/minio/pkg/sync/errgroup"
 )
 
 // BucketMetadataSys captures all bucket metadata for a given cluster.
@@ -291,21 +292,44 @@ func (sys *BucketMetadataSys) Init(ctx context.Context, buckets []BucketInfo, ob
 	return sys.load(ctx, buckets, objAPI)
 }
 
-// Loads bucket metadata for all buckets into BucketMetadataSys.
-func (sys *BucketMetadataSys) load(ctx context.Context, buckets []BucketInfo, objAPI ObjectLayer) error {
-	sys.Lock()
-	defer sys.Unlock()
-
-	for _, bucket := range buckets {
-		meta, err := loadBucketMetadata(ctx, objAPI, bucket.Name)
+// concurrently load bucket metadata to speed up loading bucket metadata.
+func (sys *BucketMetadataSys) concurrentLoad(ctx context.Context, buckets []BucketInfo, objAPI ObjectLayer) error {
+	g := errgroup.WithNErrs(len(buckets))
+	for index := range buckets {
+		index := index
+		g.Go(func() error {
+			meta, err := loadBucketMetadata(ctx, objAPI, buckets[index].Name)
+			if err != nil {
+				return err
+			}
+			sys.Lock()
+			sys.metadataMap[buckets[index].Name] = meta
+			sys.Unlock()
+			return nil
+		}, index)
+	}
+	for _, err := range g.Wait() {
 		if err != nil {
 			return err
 		}
-		sys.metadataMap[bucket.Name] = meta
 	}
 	return nil
 }
 
+// Loads bucket metadata for all buckets into BucketMetadataSys.
+func (sys *BucketMetadataSys) load(ctx context.Context, buckets []BucketInfo, objAPI ObjectLayer) error {
+	count := 100 // load 100 bucket metadata at a time.
+	for {
+		if len(buckets) < count {
+			return sys.concurrentLoad(ctx, buckets, objAPI)
+		}
+		if err := sys.concurrentLoad(ctx, buckets[:count], objAPI); err != nil {
+			return err
+		}
+		buckets = buckets[count:]
+	}
+}
+
 // NewBucketMetadataSys - creates new policy system.
 func NewBucketMetadataSys() *BucketMetadataSys {
 	return &BucketMetadataSys{