A company uses Azure Synapse Analytics dedicated SQL pool. They need to load data from Azure Data Lake Storage Gen2 (ADLS Gen2) incrementally. Which PolyBase external table configuration supports incremental loading without reprocessing historical data?
Partitioned external tables allow PolyBase to eliminate partitions, loading only new data.
Why this answer
Partitioning an external table by a date column with a partition location pattern allows PolyBase to perform partition elimination during queries. This means only the partitions containing new or modified data are read from ADLS Gen2, enabling incremental loading without scanning historical data.
Exam trap
The trap here is that candidates confuse indexing or distribution strategies (which apply to internal tables) with external table capabilities, overlooking that only partition elimination on external tables enables incremental file-level filtering in PolyBase.
How to eliminate wrong answers
Option A is wrong because a clustered index on an external table is not supported; external tables in Azure Synapse are read-only and cannot have indexes. Option C is wrong because a clustered columnstore index applies to internal tables in the dedicated SQL pool, not to external tables, and does not control which files are read from ADLS Gen2. Option D is wrong because round-robin distribution distributes data evenly across distributions but does not enable partition elimination or incremental loading; it is a distribution method for internal tables, not a mechanism for selective file reading.