In versions Adaptive Server earlier than 15.0, the segment-based, round-robin partitioning scheme supported parallel queries. However, if the partition skew exceeded a specific ratio, the optimizer considered the partitioning too unbalanced to provide effective parallel query support and process the query in serial fashion. One way to prevent this when using parallel queries is to monitor partition skews and rebalance them by dropping and re-creating the clustered index.
With semantic partitioning in Adaptive Server 15.0, data skew is no longer a consideration. Rather than evaluating the depth of the partition for parallel query optimization, the Adaptive Server optimizer considers the type of partition, the query search arguments, and so on. Because of the nature of unknown data distribution for semantic partitions, you may have data skew, but because a hash, list, or range partition signals where the data resides, the skew is unimportant.
