Apache Ignite can be configured to persist entries (native or third-party) by enabling the persistence flag, or it may not persist data at all. When native persistence is turned on, then Ignite stores entries in memory and on disk. When native persistence is turned off (either using a third-party persistence store or no persistence), then Ignite uses the off-heap memory to store the entries and allocates new pages in RAM when required. We know that Ignite's durable memory has a maximum limit (20% of RAM or an overridden value); when that limit is reached and Ignite cannot allocate a page, it purges some of the data to prevent OOM errors. This purging technique is known as eviction, and Ignite provides APIs to configure the eviction policy.

Ignite supports eviction from the following:

• Off-heap memory
• On-heap memory

The following sections will explain the off-heap and on-heap eviction policies.