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 package examples;
 
 import org.mapdb.Store;
 
This example shows how-to create off-heap cache, where entries expire when maximal store size is reached. It also shows howto get basic statistics about store size.
public class CacheOffHeap {
    public static void main(String[] args) {
        final double cacheSizeInGB = 1.0;
        // Create cache backed by off-heap store
        // In this case store will use ByteBuffers backed by byte[].
        HTreeMap cache = DBMaker.newCache(cacheSizeInGB);
        // Other alternative is to use Direct ByteBuffers.
        // In this case the memory is not released if cache is not correctly closed.
        //  cache = DBMaker.newCacheDirect(cacheSizeInGB);
        //generates random key and values
        Random r = new Random();
        //used to print store statistics
        Store store = Store.forEngine(cache.getEngine());
        // insert some stuff in cycle
        for(long counter=1; counter<1e8; counter++){
            long key = r.nextLong();
            byte[] value = new byte[1000];
            r.nextBytes(value);
            cache.put(key,value);
            if(counter%1e5==0){
                ..printf("Map size: %,d, counter %,d, store size: %,d, store free size: %,d\n",
                        cache.sizeLong(), counterstore.getCurrSize(),  store.getFreeSize());
            }
        }
        // and release memory. Only necessary with `DBMaker.newCacheDirect()`
        cache.close();
    }
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