fix: pop entries from each drives in parallel (#9918)

cmd/xl-sets.go

@@ -831,9 +831,17 @@ func (f *FileInfoCh) Push(fi FileInfo) {
 // if the caller wishes to list N entries to call lexicallySortedEntry
 // N times until this boolean is 'false'.
 func lexicallySortedEntry(entryChs []FileInfoCh, entries []FileInfo, entriesValid []bool) (FileInfo, int, bool) {
+	var wg sync.WaitGroup
 	for i := range entryChs {
-		entries[i], entriesValid[i] = entryChs[i].Pop()
+		i := i
+		wg.Add(1)
+		// Pop() entries in parallel for large drive setups.
+		go func() {
+			defer wg.Done()
+			entries[i], entriesValid[i] = entryChs[i].Pop()
+		}()
 	}
+	wg.Wait()
 
 	var isTruncated = false
 	for _, valid := range entriesValid {
@@ -915,9 +923,17 @@ func mergeEntriesCh(entryChs []FileInfoCh, maxKeys int, ndisks int) (entries Fil
 }
 
 func isTruncated(entryChs []FileInfoCh, entries []FileInfo, entriesValid []bool) bool {
+	var wg sync.WaitGroup
 	for i := range entryChs {
-		entries[i], entriesValid[i] = entryChs[i].Pop()
+		i := i
+		wg.Add(1)
+		// Pop() entries in parallel for large drive setups.
+		go func() {
+			defer wg.Done()
+			entries[i], entriesValid[i] = entryChs[i].Pop()
+		}()
 	}
+	wg.Wait()
 
 	var isTruncated = false
 	for _, valid := range entriesValid {