Refreshing data warehouses can be a challenge. Truncating and reloading tables is time-consuming and wastes I/O, but common incremental refresh techniques have their problems, too. Using date-time stamps to capture row changes, for example, can turn into a major software project and puts additional processing on source systems. Log-based replication is another possibility, but it can be tricky to set up and monitor. And while third-party tools eliminate the need for custom code, they also cost money.