Parallelism Type > EXECUTION PARALLELISM (Manual - Shards) — Defines the number of shards/partitions that the data source will use in the parsing or execution phase.
For CSV files, execution parallelism splits the source files by rows (e.g. the first row in each file would be the first shard, the second row would be the second shard, etc).
For other file formats (S3, Azure, etc), it splits it based on the files themselves (e.g. the first file in each minute would go to the first shard, the second file to the second shard, etc).
If the number of execution parallelism shards is the same as the number of shards from ingestion, then each ingestion shard is matched to an execution parallelism shard.