iOLAP is an incremental OLAP query engine that provides a smooth trade-off between query accuracy and latency, and fulfills a full spectrum of user requirements from approximate but timely query execution to a more traditional accurate query execution. iOLAP enables interactive incremental query processing using a novel mini-batch execution model---given an OLAP query, iOLAP first randomly partitions the input dataset into smaller sets (mini-batches) and then incrementally processes through these mini-batches by executing a delta update query on each mini-batch, where each subsequent delta update query computes an update based on the output of the previous one.