Caused by: org.lmdbjava.Env$ReadersFullException: Environment maxreaders reached (-30790)
at org.lmdbjava.ResultCodeMapper.checkRc(ResultCodeMapper.java:98)
at org.lmdbjava.Txn.<init>(Txn.java:67)
at org.lmdbjava.Env.txn(Env.java:361)
at org.lmdbjava.Env.txnRead(Env.java:370)
at uk.co.example.LmDbStore.getLatestDemoQCBBlock(LmDbStore.java:564)

 Dbi<ByteBuffer> demoenv = create()
            .setMapSize(20971520l)
            .setMaxDbs(5)
            .open(new File(csEnvironmentStr+"/csdbdemo"));
	demoQcbStore = demoenv.openDbi("demoQcbStoreLocn", MDB_CREATE);

final ByteBuffer key = allocateDirect(40);
    ByteBuffer val = null;
	try {
		val = toByteArray(qcb);
	} catch (IOException e) {
		logger.error("", e);			
	}

    try (Txn<ByteBuffer> txn = demoenv.txnWrite()) {    	
        key.put(id.getBytes(UTF_8)).flip();
        demoQcbStore.put(txn, key, val);
        // An explicit commit is required, otherwise Txn.close() rolls it back.
        txn.commit();
    }
...
// toByteArray and toObject are taken from: http://tinyurl.com/69h8l7x with mods for ByteBuffer
public static ByteBuffer toByteArray(Object obj) throws IOException {
    byte[] bytes = null;
    ByteArrayOutputStream bos = null;
    ObjectOutputStream oos = null;
    try {
        bos = new ByteArrayOutputStream();
        oos = new ObjectOutputStream(bos);
        oos.writeObject(obj);
        oos.flush();
        bytes = bos.toByteArray();
    } finally {
        if (oos != null) {
            oos.close();
        }
        if (bos != null) {
            bos.close();
        }
    }
    final ByteBuffer value = allocateDirect(bytes.length);
    value.put(bytes).flip();
    return  value;
}

 public QCBBlock getLatestDemoQCBBlock(String id) {
    final ByteBuffer key = allocateDirect(40);
    key.put(id.getBytes(UTF_8)).flip();
    QCBBlock block = null;
    try (Txn<ByteBuffer> txn = demoenv.txnRead()) {