gc.bufferedRenderer.leadingBufferZone=300;//下拉预加载条数(此值过大的话，将影响首次加截数据至UI可响应操作的时间)
gc.bufferedRenderer.trailingBufferZone=100;//上拉预加载条数
Ext.grid.plugin.BufferedRenderer | Ext JS 6.0.2 (sencha.com)

extjs - Enable/disable buffered rendering at runtime - Stack Overflow

var dd=Ext.ComponentQuery.query("#ExampleTreePanel")[0];
var bufferedRendererPlugin = dd.plugins[0];
bufferedRendererPlugin.setViewSize(100000);

// Set view size to match store content:
this.bufferedRenderer.setViewSize(this.getStore().getCount());
// Refresh view, so that everything is rendered:
this.bufferedRenderer.refreshView(0);
// refreshView does not revert the node container‘s "translate" setting after the viewSize was changed to be equal or greater than the store count, so we have to enforce it manually:
this.getView().getEl().down(this.getView().getNodeContainerSelector()).translate(0,0,0);

GridPanel BufferRender