diff --git a/src/sql/das/ob_das_dml_ctx_define.h b/src/sql/das/ob_das_dml_ctx_define.h
index 702a6fe07a..25849200dd 100644
--- a/src/sql/das/ob_das_dml_ctx_define.h
+++ b/src/sql/das/ob_das_dml_ctx_define.h
@@ -455,7 +455,7 @@ private:
 class ObDASDMLIterator : public common::ObNewRowIterator
 {
 public:
-  static const int64_t DEFAULT_BATCH_SIZE = 256;
+  static const int64_t DEFAULT_BATCH_SIZE = 1;
 public:
   ObDASDMLIterator(const ObDASDMLBaseCtDef *das_ctdef,
                    ObDASWriteBuffer &write_buffer,
diff --git a/src/storage/access/ob_sstable_row_scanner.cpp b/src/storage/access/ob_sstable_row_scanner.cpp
index 67371eb48f..dd96885a2e 100644
--- a/src/storage/access/ob_sstable_row_scanner.cpp
+++ b/src/storage/access/ob_sstable_row_scanner.cpp
@@ -475,7 +475,8 @@ bool ObSSTableRowScanner<ObCOPrefetcher>::can_blockscan() const
 {
   return is_scan(type_) &&
          nullptr != block_row_store_ &&
-         prefetcher_.switch_to_columnar_scan();
+         prefetcher_.switch_to_columnar_scan() &&
+         !sstable_->is_ddl_merge_sstable();
 }
 
 template<>