diff --git a/lib/logstorage/pipe_sort.go b/lib/logstorage/pipe_sort.go
index 2e7d42d29..a0e3366f2 100644
--- a/lib/logstorage/pipe_sort.go
+++ b/lib/logstorage/pipe_sort.go
@@ -399,6 +399,10 @@ func (psp *pipeSortProcessor) flush() error {
 			sh = append(sh, shard)
 		}
 	}
+	if len(sh) == 0 {
+		return nil
+	}
+
 	heap.Init(&sh)
 
 	wctx := &pipeSortWriteContext{
@@ -413,6 +417,13 @@ func (psp *pipeSortProcessor) flush() error {
 		if shard.rowRefNext >= uint(len(shard.rowRefs)) {
 			_ = heap.Pop(&sh)
 			shardNext = nil
+
+			select {
+			case <-psp.stopCh:
+				return nil
+			default:
+			}
+
 			continue
 		}
 
@@ -473,7 +484,7 @@ func (wctx *pipeSortWriteContext) writeRow(shard *pipeSortProcessorShard, rowIdx
 		// send the current block to bbBase and construct new columns
 		wctx.flush()
 
-		rcs = rcs[:0]
+		rcs = wctx.rcs[:0]
 		for _, bf := range byFields {
 			rcs = append(rcs, resultColumn{
 				name: bf.name,