Recently, at one of the customer meetings, I was asked whether GridGain comes with its own database. Naturally my reaction was – why? GridGain easily integrates pretty much with any persistent store you wish, including any RDBMS, NoSql, or HDFS stores. However, then I thought, why not? We already have cache swap space (disk overflow) storage based on Google LevelDB key-value database implementation, so why not have the same for data store.

Here is how easy it was to add LevelDB based data store implementation for GridGain cache – literally took me 20 minutes to do, including unit tests. The store is based on GridGain swap space, but since swap space is based on LevelDB, you essentially get LevelDB local store for your cached data.

public class GridCacheSwapSpaceStore<K, V>
    extends GridCacheStoreAdapter<K, V> {
    private ClassLoader dfltLdr = getClass().getClassLoader();

    @GridInstanceResource
    private Grid g; // Auto-injected grid instance

    @Override
    public V load(String cacheName, GridCacheTx tx, K key)
        throws GridException {
        return g.readFromSwap(spaceName(cacheName), key,
            classLoader(key));
    }

    @Override
    public void put(String cacheName, GridCacheTx tx, K key, V val)
        throws GridException {
        g.writeToSwap(spaceName(cacheName), key, val,
             classLoader(val, key));
    }

    @Override
    public void remove(String cacheName, GridCacheTx tx, K key)
        throws GridException {
        g.removeFromSwap(spaceName(cacheName), key, null,
            classLoader(key));
    }

    private String spaceName(String cacheName) {
        return cacheName == null ?
            "gg-st-default" : "gg-st-" + cacheName;
    }

    private ClassLoader classLoader(Object... objs) {
        ClassLoader ldr = null;

        for (Object o : objs) {
            if (o != null) {
                ldr = U.detectClassLoader(o.getClass());

                if (ldr != dfltLdr)
                    break;
            }
        }

        return ldr;
    }
}

Quite easily done in my view. Plenty of more examples of different GridGain cache store implementations can be found on GitHub here.