What is the best approach to check for uneven data allocation across distributions?

The best approach to check for uneven data allocation across distributions is to use DBCC PDW_SHOWSPACEUSED. This command provides valuable insights into the distribution of data across different distributions within a table in a distributed database environment, specifically SQL Data Warehouse (now Azure Synapse Analytics).

When executed, DBCC PDW_SHOWSPACEUSED returns detailed information about each distribution, including the number of rows, space used, and other metrics. By examining the number of rows in each distribution, you can quickly identify any imbalances in data allocation. If one distribution has significantly more rows than others, it indicates uneven data distribution, which may lead to performance issues during query execution as certain distributions may work harder than others.

This method is efficient and directly targeted at assessing data distribution, making it the most effective choice for analyzing how data is spread across partitions in a distributed system. It provides a clear, actionable insight that can help in further optimizing data loading and query performance strategies.