|General Region Data Management / Eviction|
Eviction settings cause Pivotal GemFire to work to keep a region's resource use under a specified level by removing least recently used (LRU) entries to make way for new entries.
You configure for eviction based on entry count, percentage of available heap, and absolute memory usage. You also configure what to do when you need to evict: destroy entries or overflow them to disk. See Persistence and Overflow.
When GemFire determines that adding or updating an entry would take the region over the specified level, it overflows or removes enough older entries to make room. For entry count eviction, this means a one-to-one trade of an older entry for the newer one. For the memory settings, the number of older entries that need to be removed to make space depends entirely on the relative sizes of the older and newer entries.
Because of this, eviction in partitioned regions may leave older entries for the region in other buckets in the local data store as well as in other stores in the distributed system. It may also leave entries in a primary copy that it evicts from a secondary copy or vice-versa.