One of the world leaders in Retail had some massive performance issues. We optimised their queries and helped them reach some decent performance, customer satisfaction improving from “Very Frustrated” to “Very Satisfied”. Some of the queries went from 15 hours to 3 seconds.
To get there we collected some traces to get the bottlenecks and the top consuming queries. To optimise those queries, we used different techniques such as updating the statistics more frequently for certain tables, adding the right indexes, creating plan guides, adding query hints (optimise for unknown or old cardinality estimator).