Administration guide > Plan the WebSphere eXtreme Scale environment > Cache topology
Local in-memory cache
Local in-memory cache scenario
In the simplest case, eXtreme Scale can be used as a local (non-distributed) in-memory data grid cache. The local case can especially benefit high-concurrency applications where multiple threads need to access and modify transient data. The data kept in a local WXS grid can be indexed and retrieved using WXS's query support.
The ability to query the data when working with large in memory data sets versus the limited data structure support provided with the JVM, which is ready to use as is.
The local in-memory cache topology for WXS provides consistent, transactional access to temporary data within a single JVM.
Advantages
- Simple setup
An ObjectGrid can be created programmatically or declaratively with the ObjectGrid deployment descriptor XML file or with other frameworks such as Spring.
- Fast
Each BackingMap can be independently tuned for optimal memory utilization and concurrency.
- Ideal for single-JVM topologies with small dataset or for caching frequently accessed data.
- Transactional
BackingMap updates can be grouped into a single unit of work and can be integrated as a last participant in 2-phase transactions such as Java Transaction Architecture (JTA) transactions.
Disadvantages
- Not fault tolerant.
- The data is not replicated. In-memory caches are best for read-only reference data.
- Not scalable. The amount of memory required by the database might overwhelm the JVM.
- Problems occur when adding JVMs:
- Data cannot be partitioned
- Must manually replicate state between JVMs or each cache instance could have different versions of the same data.
- Invalidation is expensive.
- Each cache must be warmed up independently. The warm-up is the period of loading a set of data so that the cache gets populated with valid data.
- Data cannot be partitioned
When to use
The local, in-memory cache deployment topology should only be used when the amount of data to be cached is small (can fit into a single JVM) and is relatively stable. Stale data must be tolerated with this approach. Using evictors to keep most frequently or recently used data in the cache can help keep the cache size low and increase relevance of the data.
Parent topic:
Cache topology: In-memory and distributed caching
Related concepts
Peer-replicated local cache
Distributed cache
Embedded cache
Multi-master data grid replication topologies