I would say that Spark is a good product for interactive analytics, while Ignite is better for real-time analytics and high performance transactional processing. Ignite achieves this by providing efficient and scalable in-memory key-value storage, as well as rich capabilities for indexing, querying the data and running computations.
Another common use for Ignite is distributed caching, which is often used to improve performance of applications that interact with relational databases or any other data sources.
probably OLAP and OLTP are more correct terms here. The former implies running comparatively rare, large and mostly read-only queries, while in the latter there is high throughput of smaller queries. Ignite was initially designed for OLTP, but currently addresses OLAP as well.
https://stackoverflow.com/questions/36036910/apache-spark-vs-apache-ignite