A test case showing that leveldb compaction don't work so good /w sequencial insert and delete. Related to a mailing list post[1] and a reported bug [2]. [1]: https://groups.google.com/d/msg/leveldb/yL6h1mAOc20/vLU64RylIdMJ [2]: https://code.google.com/p/leveldb/issues/detail?id=77

DBCompactionTest.java

import org.fusesource.leveldbjni.JniDBFactory;
import org.iq80.leveldb.*;

import java.io.File;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.util.Random;

public class DBCompactionTest {

    public static void main(String args[]) throws IOException, DBException {

        Options options = new Options().createIfMissing(true);
        WriteOptions wo = new WriteOptions().sync(false);

        JniDBFactory.factory.destroy(new File("test-data"), options);
        DB db = JniDBFactory.factory.open(new File("test-data"), options);

        Random rand = new Random();
        ByteBuffer key = ByteBuffer.allocate(8);
        byte[] value = new byte[1024];

        // Lets try to generate about 40 MB of live data.
        long liveKeys = (1024*1024*40)/(value.length+key.capacity()+12);
        long totalKeys = liveKeys * 50;

        for( long i=0; i < totalKeys; i++) {

            if( i%((totalKeys/100)*10) == 0 ) {
                long[] approximateSizes = db.getApproximateSizes(new Range[]{new Range(new byte[]{0},new byte[]{1})});
                System.out.println(String.format("%d%% done. Using: %,2f MB", (i / (totalKeys/100)), (approximateSizes[0]/(1024.0*1024))));
                // System.out.println(db.getProperty("leveldb.stats"));
            }

            key.clear();
            rand.nextBytes(value);
            db.put(key.putLong(i).array(), value, wo);
            if( i >= liveKeys ) {
                long deleteKey = i - liveKeys;
                if( deleteKey == 0 ) {
                    long[] approximateSizes = db.getApproximateSizes(new Range[]{new Range(new byte[]{0},new byte[]{1})});
                    System.out.println(String.format("Deletes starting.  %d%% done. Using: %,2f MB", (i / (totalKeys/100)), (approximateSizes[0]/(1024.0*1024))));
                }
                key.clear();
                db.delete(key.putLong(deleteKey).array(), wo);
            }
        }

        System.out.println("Deleting remaining live records...");
        // lets delete the remaining live keys.
        for( long i=totalKeys-liveKeys; i < totalKeys; i++) {
            key.clear();
            db.delete(key.putLong(i).array(), wo);
        }

        System.out.println("Counting records...");

        // Lets verify none of the keys are left.
        int entries =0 ;
        DBIterator iterator = db.iterator();
        iterator.seekToFirst();
        while( iterator.hasNext() ) {
            iterator.next();
            entries++;
        }
        System.out.println("Database contained "+entries+" entries.");
        long[] approximateSizes = db.getApproximateSizes(new Range[]{new Range(new byte[]{0},new byte[]{1})});
        System.out.println(String.format("Using: %,2f MB", (approximateSizes[0]/(1024.0*1024))));

        db.close();
    }

}