Requirements: 
MODORDERS-488 Investigate transition of Orders search to cross-index subqueries
Overview:
Endpoints calling views:
/orders-storage/receiving-history → receiving_history_view
/orders-storage/orders → orders_view
/orders-storage/po-lines → po_lines_view
/orders-storage/order-lines → order_lines_view
Prepared a POC with migration of this endpoint from searching accross the views to the searching via cross-indexes
Performance improvements:
For the perfomance testing purposes I have prepared data loading script which creates 100 purchase orders and 50.000 PO lines in total. Each poline slightly differs from other only by listUnitPrice, so search requests will be performed quering this field by value.
Results of the search across the views:
Query example /orders-storage/order-lines?query=workflowStatus==Pending and cost.listUnitPrice==21.0
As you can see every search requests takes almost 2 seconds
Results of the search via cross index approach:
Query example differs a bit according to cross index syntax: /orders-storage/order-lines?query=purchaseOrder.workflowStatus==Pending and cost.listUnitPrice==21.0
As you can see every search requests takes less than 200 ms
So switching implementation from views to the cross index search improves perfomance about 10 times.