In a traditional RDBMS, you have atomic transactions, which is true for Datastore as well. Datastore does support atomic transactions and the ACID properties, mostly due to the need to keep all of the internal indices consistent. Both traditional RDBMS and Datastore make heavy use of indices for fast lookup. But in Datastore, every query makes use of indices, which is far beyond what traditional RDBMS do. Consequently, the query execution time in Datastore is basically independent of the size of the underlying dataset, which is certainly not the case with traditional RDBMSs.
Traditional RDBMS use relational data, that is, rows and columns, but without many hierarchical relationships within those entity relations. Datastore on the other hand is document-oriented, which implies it is optimized for hierarchically structured data such as XML or...
