Unit of work is based on the setting of the BulkCommitCount property.
If BulkCommitCount is set to 0, the entire transfer is treated as a unit of work. The access service performs a commit after the last row of data is inserted into the target table, even if value errors occurred for individual rows of the transfer.
If BulkCommitCount is set to a non zero value, each block of BulkCommitCount rows is treated as a unit of work. The access service issues a commit after each block of BulkCommitCount rows.
If BulkCommitCount is set to 50, each block of 50 rows is treated as a unit of work, and a commit is issued after each 50 rows.