If you ever looked at Apache® Ignite^tm, you have probably noticed that it is a fairly rich platform with lots of components. However, despite the extensive feature set, Ignite community aims to make the platform easy to use and understand. Here is how the Ignite community defines their project:

Apache Ignite is an in-memory computing platform that is durable, strongly consistent, and highly available with powerful SQL, key-value, and processing APIs.

So, in summary, Ignite looks like a distributed data storage that can work both in-memory and on-disk, and provides SQL, key-value, and processing APIs to the data. Sounds simple enough. However, to get a complete picture, perhaps it is better to define Ignite by answering several "Is Ignite a...?" questions:

Is Ignite a persistent or pure in-memory storage?

Both. Native persistence in Ignite can be turned on and off. This allows Ignite to store datasets bigger than can fit in the available memory. Essentially, the smaller operational data sets can be stored in-memory only, and larger datasets that do not fit in-memory can be stored on-n disk, using memory as a caching layer for better performance.

Is Ignite an in-memory database (IMDB)?

Yes. Even though Ignite durable memory works well in-memory and on-disk, the disk persistence can be disabled and Ignite can act as a pure distributed in-memory database with support for SQL and distributed joins.

Is Ignite an in-memory data grid (IMDG)?

Yes. Ignite is a full-featured data grid that can be used either in either pure in-memory mode or with Ignite native persistence. It can also automatically integrate with any third-party databases, including any RDBMS or NoSQL stores.

Is Ignite a distributed database?

Yes. Data in Ignite is either partitioned or replicated across a cluster of multiple nodes. This provides scalability and adds resiliency to the system. Ignite automatically controls how data is partitioned; however, users can plug in their own distribution (affinity) functions and collocate various pieces of data together for efficiency.

Is Ignite an SQL database?

Not fully. Although Ignite aims to behave like any other relational SQL database, there are differences in how Ignite handles constraints and indexes. Ignite supports primary and secondary indexes; however, the uniqueness can only be enforced for the primary indexes. Ignite also does not support foreign key constraints.

Essentially, Ignite purposely does not support any constraints that would entail a cluster broadcast message for each update and significantly hurt performance and scalability of the system.

Is Ignite a transactional database?

Not fully. ACID transactions are supported, but only at the key-value API level. Ignite also supports cross-partition transactions, which means that transactions can span keys residing in different partitions on different servers. At the SQL level, Ignite supports atomic, but not yet transactional consistency. Ignite community plans to implement SQL transactions in version 2.4.

Is Ignite a key-value store?

Yes. Ignite provides a feature-rich key-value API that is JCache (JSR-107) compliant and supports Java, C++, and.NET.

You can find out more about Ignite by visiting the freshly redesigned Ignite website.