[enhancement](load) Increase batch size of node channel to improve import performance (#13912)

be/src/vec/sink/vtablet_sink.cpp

@@ -68,6 +68,12 @@ Status VNodeChannel::init(RuntimeState* state) {
     _cur_add_block_request.set_eos(false);
 
     _name = fmt::format("VNodeChannel[{}-{}]", _index_channel->_index_id, _node_id);
+    // The node channel will send _batch_size rows of data each rpc. When the
+    // number of tablets is large, the number of data rows received by each
+    // tablet is small, TabletsChannel need to traverse each tablet for import.
+    // so the import performance is poor. Therefore, we set _batch_size to
+    // a relatively large value to improve the import performance.
+    _batch_size = std::max(_batch_size, 8192);
 
     return Status::OK();
 }