Question

I’m looking for an in-memory cache with the following behaviour.

• On the first access or after initialization it read’s all data to be cached at once. E.g. all rows of a table.
• After one hour the complete cache is cleared and all data is read again at once.
• The cache could be cleared on demand.

I know how to implement such a cache, but does anybody know an existing library, which provides a cache like this.

This is my idea about the interface. There are elements for the cache

Element element = new Element(Object key, Object objectToCache);

A loader provides all elements

Collection<Element> elements = myLoader.getElements();

In the end there is the cache

public Cache {
  public Cache(CacheLoader loader, int timeToReload) {
    ...
  }

  public Object getValueForKey(Object key {
    ...
  }

  ...
}

---

A solution would be to have a cache with a single entry, which is a HashMap of the real entries. With this solution I can use existing caches like Ehcache or Guava Caches.

But nevertheless I’m looking for existing code, before I start writing a own library.

Answer 1

Do you look for some kind of distributed cache and want spread the initial load over many instances, right?

Hazlecast persistent datastore API is always worth a look.

Hazlecast Doc

Initialization on startup As of 1.9.3 MapLoader has the new MapLoader.loadAllKeys API. It is used for pre-populating the in-memory map when the map is first touched/used. If MapLoader.loadAllKeys returns NULL then nothing will be loaded. Your MapLoader.loadAllKeys implementation can return all or some of the keys. You may select and return only the hot keys, for instance. Also note that this is the fastest way of pre-populating the map as Hazelcast will optimize the loading process by having each node loading owned portion of the entries.

In combination with the hazelcast.initial.min.cluster.size configuration property you can distribute your initial load.