diff --git a/includes/abstracts/abstract-wc-order.php b/includes/abstracts/abstract-wc-order.php
index 0f75607e39b..0da59900fee 100644
--- a/includes/abstracts/abstract-wc-order.php
+++ b/includes/abstracts/abstract-wc-order.php
@@ -51,13 +51,7 @@ abstract class WC_Abstract_Order extends WC_Abstract_Legacy_Order {
 	 * @since 2.7.0
 	 * @var array
 	 */
-	protected $items = array(
-		'line_items'     => null,
-		'coupon_lines'   => null,
-		'shipping_lines' => null,
-		'fee_lines'      => null,
-		'tax_lines'      => null,
-	);
+	protected $items = array();
 
 	/**
 	 * Order items that need deleting are stored here.
@@ -642,6 +636,7 @@ abstract class WC_Abstract_Order extends WC_Abstract_Legacy_Order {
 
 	/**
 	 * Remove all line items (products, coupons, shipping, taxes) from the order.
+	 *
 	 * @param string $type Order item type. Default null.
 	 */
 	public function remove_order_items( $type = null ) {
@@ -649,22 +644,17 @@ abstract class WC_Abstract_Order extends WC_Abstract_Legacy_Order {
 			$this->data_store->delete_items( $this, $type );
 
 			if ( $group = $this->type_to_group( $type ) ) {
-				$this->items[ $group ] = null;
+				unset( $this->items[ $group ] );
 			}
 		} else {
 			$this->data_store->delete_items( $this );
-			$this->items = array(
-				'line_items'     => null,
-				'coupon_lines'   => null,
-				'shipping_lines' => null,
-				'fee_lines'      => null,
-				'tax_lines'      => null,
-			);
+			$this->items = array();
 		}
 	}
 
 	/**
 	 * Convert a type to a types group.
+	 *
 	 * @param string $type
 	 * @return string group
 	 */
@@ -681,6 +671,7 @@ abstract class WC_Abstract_Order extends WC_Abstract_Legacy_Order {
 
 	/**
 	 * Return an array of items/products within this order.
+	 *
 	 * @param string|array $types Types of line items to get (array or string).
 	 * @return Array of WC_Order_item
 	 */
@@ -690,7 +681,7 @@ abstract class WC_Abstract_Order extends WC_Abstract_Legacy_Order {
 
 		foreach ( $types as $type ) {
 			if ( $group = $this->type_to_group( $type ) ) {
-				if ( is_null( $this->items[ $group ] ) ) {
+				if ( ! isset( $this->items[ $group ] ) ) {
 					$this->items[ $group ] = $this->data_store->read_items( $this, $type );
 				}
 				// Don't use array_merge here because keys are numeric
@@ -703,6 +694,7 @@ abstract class WC_Abstract_Order extends WC_Abstract_Legacy_Order {
 
 	/**
 	 * Return an array of fees within this order.
+	 *
 	 * @return array
 	 */
 	public function get_fees() {
@@ -711,6 +703,7 @@ abstract class WC_Abstract_Order extends WC_Abstract_Legacy_Order {
 
 	/**
 	 * Return an array of taxes within this order.
+	 *
 	 * @return array
 	 */
 	public function get_taxes() {
@@ -719,6 +712,7 @@ abstract class WC_Abstract_Order extends WC_Abstract_Legacy_Order {
 
 	/**
 	 * Return an array of shipping costs within this order.
+	 *
 	 * @return array
 	 */
 	public function get_shipping_methods() {
@@ -727,6 +721,7 @@ abstract class WC_Abstract_Order extends WC_Abstract_Legacy_Order {
 
 	/**
 	 * Gets formatted shipping method title.
+	 *
 	 * @return string
 	 */
 	public function get_shipping_method() {
@@ -739,6 +734,7 @@ abstract class WC_Abstract_Order extends WC_Abstract_Legacy_Order {
 
 	/**
 	 * Get coupon codes only.
+	 *
 	 * @return array
 	 */
 	public function get_used_coupons() {
@@ -770,6 +766,7 @@ abstract class WC_Abstract_Order extends WC_Abstract_Legacy_Order {
 
 	/**
 	 * Get an order item object, based on it's type.
+	 *
 	 * @since  2.7.0
 	 * @param  int $item_id
 	 * @return WC_Order_Item
@@ -780,6 +777,7 @@ abstract class WC_Abstract_Order extends WC_Abstract_Legacy_Order {
 
 	/**
 	 * Get key for where a certain item type is stored in _items.
+	 *
 	 * @since  2.7.0
 	 * @param  $item object Order item (product, shipping, fee, coupon, tax)
 	 * @return string
@@ -802,6 +800,7 @@ abstract class WC_Abstract_Order extends WC_Abstract_Legacy_Order {
 
 	/**
 	 * Remove item from the order.
+	 *
 	 * @param int $item_id
 	 */
 	public function remove_item( $item_id ) {
@@ -818,6 +817,7 @@ abstract class WC_Abstract_Order extends WC_Abstract_Legacy_Order {
 
 	/**
 	 * Adds an order item to this order. The order item will not persist until save.
+	 *
 	 * @since 2.7.0
 	 * @param WC_Order_Item Order item object (product, shipping, fee, coupon, tax)
 	 */
@@ -827,7 +827,7 @@ abstract class WC_Abstract_Order extends WC_Abstract_Legacy_Order {
 		}
 
 		// Make sure existing items are loaded so we can append this new one.
-		if ( is_null( $this->items[ $items_key ] ) ) {
+		if ( ! isset( $this->items[ $items_key ] ) ) {
 			$this->items[ $items_key ] = $this->get_items( $item->get_type() );
 		}
 
@@ -845,6 +845,7 @@ abstract class WC_Abstract_Order extends WC_Abstract_Legacy_Order {
 	/**
 	 * Add a product line item to the order. This is the only line item type with
 	 * it's own method because it saves looking up order amounts (costs are added up for you).
+	 *
 	 * @param  \WC_Product $product
 	 * @param  int $qty
 	 * @param  array $args
diff --git a/includes/class-wc-order-factory.php b/includes/class-wc-order-factory.php
index 63ec1d6b2a7..1d25200ca7a 100644
--- a/includes/class-wc-order-factory.php
+++ b/includes/class-wc-order-factory.php
@@ -45,7 +45,15 @@ class WC_Order_Factory {
 		}
 
 		try {
-			return new $classname( $order_id );
+			// Try to get from cache, otherwise create a new object,
+			$order = wp_cache_get( 'order-' . $order_id, 'orders' );
+
+			if ( ! is_a( $order, 'WC_Order' ) ) {
+				$order = new $classname( $order_id );
+				wp_cache_set( 'order-' . $order_id, $order, 'orders' );
+			}
+
+			return $order;
 		} catch ( Exception $e ) {
 			return false;
 		}
@@ -97,7 +105,15 @@ class WC_Order_Factory {
 			}
 			if ( $classname ) {
 				try {
-					return new $classname( $id );
+					// Try to get from cache, otherwise create a new object,
+					$item = wp_cache_get( 'order-item-' . $id, 'order-items' );
+
+					if ( ! is_a( $item, 'WC_Order_Item' ) ) {
+						$item = new $classname( $id );
+						wp_cache_set( 'order-item-' . $id, $item, 'order-items' );
+					}
+
+					return $item;
 				} catch ( Exception $e ) {
 					return false;
 				}
diff --git a/includes/class-wc-order-item-product.php b/includes/class-wc-order-item-product.php
index 902dde5366a..e8d971dc8d0 100644
--- a/includes/class-wc-order-item-product.php
+++ b/includes/class-wc-order-item-product.php
@@ -196,8 +196,9 @@ class WC_Order_Item_Product extends WC_Order_Item {
 	 * Set meta data for backordered products.
 	 */
 	public function set_backorder_meta() {
-		if ( $this->get_product()->backorders_require_notification() && $this->get_product()->is_on_backorder( $this->get_quantity() ) ) {
-			$this->add_meta_data( apply_filters( 'woocommerce_backordered_item_meta_name', __( 'Backordered', 'woocommerce' ) ), $this->get_quantity() - max( 0, $this->get_product()->get_stock_quantity() ), true );
+		$product = $this->get_product();
+		if ( $product && $product->backorders_require_notification() && $product->is_on_backorder( $this->get_quantity() ) ) {
+			$this->add_meta_data( apply_filters( 'woocommerce_backordered_item_meta_name', __( 'Backordered', 'woocommerce' ) ), $this->get_quantity() - max( 0, $product->get_stock_quantity() ), true );
 		}
 	}
 
diff --git a/includes/data-stores/abstract-wc-order-data-store-cpt.php b/includes/data-stores/abstract-wc-order-data-store-cpt.php
index d09aed05f37..d8983cf526d 100644
--- a/includes/data-stores/abstract-wc-order-data-store-cpt.php
+++ b/includes/data-stores/abstract-wc-order-data-store-cpt.php
@@ -242,6 +242,7 @@ abstract class Abstract_WC_Order_Data_Store_CPT extends WC_Data_Store_WP impleme
 	protected function clear_caches( &$order ) {
 		clean_post_cache( $order->get_id() );
 		wc_delete_shop_order_transients( $order );
+		wp_cache_delete( 'order-' . $order->get_id(), 'orders' );
 	}
 
 	/**
diff --git a/includes/data-stores/abstract-wc-order-item-type-data-store.php b/includes/data-stores/abstract-wc-order-item-type-data-store.php
index 1db17c22477..a9fc5536a34 100644
--- a/includes/data-stores/abstract-wc-order-item-type-data-store.php
+++ b/includes/data-stores/abstract-wc-order-item-type-data-store.php
@@ -45,6 +45,7 @@ abstract class Abstract_WC_Order_Item_Type_Data_Store extends WC_Data_Store_WP i
 		$this->save_item_data( $item );
 		$item->save_meta_data();
 		$item->apply_changes();
+		$this->clear_cache( $item );
 
 		do_action( 'woocommerce_new_order_item', $item->get_id(), $item, $item->get_order_id() );
 	}
@@ -67,6 +68,7 @@ abstract class Abstract_WC_Order_Item_Type_Data_Store extends WC_Data_Store_WP i
 		$this->save_item_data( $item );
 		$item->save_meta_data();
 		$item->apply_changes();
+		$this->clear_cache( $item );
 
 		do_action( 'woocommerce_update_order_item', $item->get_id(), $item, $item->get_order_id() );
 	}
@@ -126,6 +128,6 @@ abstract class Abstract_WC_Order_Item_Type_Data_Store extends WC_Data_Store_WP i
 	 * Clear meta cachce.
 	 */
 	public function clear_cache( &$item ) {
-		WC_Cache_Helper::incr_cache_prefix( 'orders' );
+		wp_cache_delete( 'order-item-' . $item->get_id(), 'order-items' );
 	}
 }
diff --git a/includes/data-stores/class-wc-order-item-coupon-data-store.php b/includes/data-stores/class-wc-order-item-coupon-data-store.php
index b4ee16a62a7..202e699eb5b 100644
--- a/includes/data-stores/class-wc-order-item-coupon-data-store.php
+++ b/includes/data-stores/class-wc-order-item-coupon-data-store.php
@@ -51,6 +51,5 @@ class WC_Order_Item_Coupon_Data_Store extends Abstract_WC_Order_Item_Type_Data_S
 		foreach ( $save_values as $key => $value ) {
 			update_metadata( 'order_item', $id, $key, $value );
 		}
-		$this->clear_cache( $item );
 	}
 }
diff --git a/includes/data-stores/class-wc-order-item-fee-data-store.php b/includes/data-stores/class-wc-order-item-fee-data-store.php
index 76a7d0ab00b..bb638631f3c 100644
--- a/includes/data-stores/class-wc-order-item-fee-data-store.php
+++ b/includes/data-stores/class-wc-order-item-fee-data-store.php
@@ -55,6 +55,5 @@ class WC_Order_Item_Fee_Data_Store extends Abstract_WC_Order_Item_Type_Data_Stor
 		foreach ( $save_values as $key => $value ) {
 			update_metadata( 'order_item', $id, $key, $value );
 		}
-		$this->clear_cache( $item );
 	}
 }
diff --git a/includes/data-stores/class-wc-order-item-product-store.php b/includes/data-stores/class-wc-order-item-product-store.php
index 4050fc005b7..748db13bf3c 100644
--- a/includes/data-stores/class-wc-order-item-product-store.php
+++ b/includes/data-stores/class-wc-order-item-product-store.php
@@ -62,7 +62,6 @@ class WC_Order_Item_Product_Data_Store extends Abstract_WC_Order_Item_Type_Data_
 		foreach ( $save_values as $key => $value ) {
 			update_metadata( 'order_item', $id, $key, $value );
 		}
-		$this->clear_cache( $item );
 	}
 
 	/**
diff --git a/includes/data-stores/class-wc-order-item-shipping-data-store.php b/includes/data-stores/class-wc-order-item-shipping-data-store.php
index 7588aaf1a3a..af52d77b14c 100644
--- a/includes/data-stores/class-wc-order-item-shipping-data-store.php
+++ b/includes/data-stores/class-wc-order-item-shipping-data-store.php
@@ -53,6 +53,5 @@ class WC_Order_Item_Shipping_Data_Store extends Abstract_WC_Order_Item_Type_Data
 		foreach ( $save_values as $key => $value ) {
 			update_metadata( 'order_item', $id, $key, $value );
 		}
-		$this->clear_cache( $item );
 	}
 }
diff --git a/includes/data-stores/class-wc-order-item-tax-data-store.php b/includes/data-stores/class-wc-order-item-tax-data-store.php
index d620cc2f4c0..96df2129e55 100644
--- a/includes/data-stores/class-wc-order-item-tax-data-store.php
+++ b/includes/data-stores/class-wc-order-item-tax-data-store.php
@@ -56,6 +56,5 @@ class WC_Order_Item_Tax_Data_Store extends Abstract_WC_Order_Item_Type_Data_Stor
 		foreach ( $save_values as $key => $value ) {
 			update_metadata( 'order_item', $id, $key, $value );
 		}
-		$this->clear_cache( $item );
 	}
 }