Archive for October, 2008

Branching and Merging

October 22nd, 2008 bleiente Comments off

Everybody is talking about subversion (svn), branches, and merging these days, so I collected some resources from the net.

  • There is the online version of the book Version Control with Subversion which covers the basics and advanced stuff as well as all svn commands in detail.
  • The German site accompanies the print edition and also hosts a discussion forum.
  • If you’re looking for further links to clients, articles, etc. try the Javapedia.

And here are some interesting recent blog entries which focus on the art of branching and merging:

We’ll have a discussion round on this topic soon, so let’s see what we will come up with…

parallelization + array = ParallelArray

October 17th, 2008 AVC Comments off

The idea is that a ParallelArray represents a collection of structurally similar data items, and you use the methods on ParallelArray to create a description of how you want to slice and dice the data. You then use the description to actually execute the array operations, which uses the fork-join framework under the hood, in parallel…This idea coming in JDK 7 :)

In fact, here are some operations supported by ParallelArray:

  • Filtering: selecting a subset of the elements
  • Mapping: convert selected elements to another form
  • Replacement: create a new ParallelArray derived from the original
  • Aggregation: combine all values into a single value
  • Application: perform an action for each selected element

- avc

Categories: 16ms, Coding, Common, Java, Technology Tags:

Too lazy to architecturize your projects?

October 17th, 2008 derlanders 2 comments

Here is the solution:


Intelligent Route Balancing & Consistent Hashing Algorithm…

October 10th, 2008 AVC Comments off

I have run into consistent hashing a couple of times. So what is consistent hashing and why should you care?

The need for consistent hashing arose from limitations experienced while running collections of caching machines. The common way, if you have a collection of n cache machines, is to put the object o in cache machine number hash(o) mod n.This shude works until you remove or add a cache machine. The reason then n changes and every object is hashed to a new location

The conclusion of that is , it would be usefull if a cache machine was added, it took its fair share of objects from all the other cache machines or when a cache machine was removed the objects were shared between the remaining machines.

Thats was what consistent hashing does – consistently maps objects to the same cache machine, as far as is possible, at least.

Architecture with consistent hashing and route balancing in a Grid (yes it a data-grid):


This  diagram illustrates the difference between using route balancing in data grid or without route balancing . The left side shows execution flow without route balancing. In this case the data is then delivered to caller (master) node that call the back nodes ,wich can be a Cache Node. This case can be faster than DB access, but results into unnecessary network traffic.

The right side you can see the routing and balancing. The whole computation logic together with data access logic is brought to data server for local execution. Assuming that serialization of computation logic is much lighter than serializing data, the network traffic in this case is minimal. Also, your computation may access data from both, Node 2 and Node 3.This case is without unnecessary network traffic and quit fast than DB access.

That’s is the idea behind the Intelligent Route Balancing  Consistent Hashing Algorithm :)

-avc (Arkadiusz Victor Czarnik)

Categories: 16ms Tags:

Use MemCacheStore in Tomcat…

October 10th, 2008 AVC Comments off


memcache-client is a Java interface to memcached; memcached is a distributed caching system. Originally, memcached was developed for, which was one of the earliest popular blogging communities. It is reported that the newly developed memcached was able to decrease LiveJournal’s database load to nearly nothing using only existing hardware. For a site that at the time handled over 20 million page views a day and had over a million different users, that’s very significant. A number of other popular sites use memcached, including Slashdot and Wikipedia. This section describes how to setup  MemCache with Sessionstore module from Tomcat 5.x(it works in jboss also). A simple class that implements Store interface and use a memcacheclient to store sessions.

Hier is a simple MemCacheStore class that implemts all functionality:

import com.danga.MemCached.MemCachedClient;
import com.danga.MemCached.SockIOPool;

 * Implementation of a Tomcat Session {@link Store} that's backed by
 * memcached.
 * @author avc
public class MemCacheStore extends StoreBase implements Store {

	 * The descriptive information about this implementation.
	protected static String info = "MemCacheStore/1.0";

	 * The thread safe and thread local memcacheclient instance.
	private static final ThreadLocal<MemCachedClient> memclient = new ThreadLocal<MemCachedClient>();

	 * The server list for memcache connections.
	private List<String> servers = new ArrayList<String>();

	 * all keys for current request session.
	private List<String> keys = Collections
			.synchronizedList(new ArrayList<String>());

	 * Return the info for this Store.
	public String getInfo() {
		return (info);

	 * Clear all sessions from the cache.
	public void clear() throws IOException {

	 * Return local keyList size.
	public int getSize() throws IOException {
		return getKeyList().size();

	 * Return all keys
	public String[] keys() throws IOException {
		return getKeyList().toArray(new String[] {});

	 * Load the Session from the cache with given sessionId.
	public Session load(String sessionId) throws ClassNotFoundException,
			IOException {

		try {

			byte[] bytes = (byte[]) getMemcacheClient().get(sessionId);
			if (bytes == null)
				return null;
			ObjectInputStream ois = bytesToObjectStream(bytes);

			StandardSession session = (StandardSession) manager
			if (session.isValid() && !keys.contains(sessionId)) {
			return session;

		} catch (Exception e) {
			return (null);

	 * transform a vaild Session from objectinputstream.
	 * Check which classLoader is responsible for the current instance.
	 * @param bytes
	 * @return ObjectInputStream with the Session object.
	 * @throws IOException
	private ObjectInputStream bytesToObjectStream(byte[] bytes)
			throws IOException {
		ByteArrayInputStream bais = new ByteArrayInputStream(bytes);
		ObjectInputStream ois = null;
		Loader loader = null;
		ClassLoader classLoader = null;
		Container container = manager.getContainer();
		if (container != null)
			loader = container.getLoader();
		if (loader != null)
			classLoader = loader.getClassLoader();
		if (classLoader != null)
			ois = new CustomObjectInputStream(bais, classLoader);
			ois = new ObjectInputStream(bais);
		return ois;

	 * remove the session with given sessionId
	public void remove(String sessionId) throws IOException {
		List<String> keyList = getKeyList();

	 * Store a objectstream from the session into the cache.
	public void save(Session session) throws IOException {
		ByteArrayOutputStream baos = new ByteArrayOutputStream();
		ObjectOutputStream oos = new ObjectOutputStream(baos);
		StandardSession standard = (StandardSession) session;
		getMemcacheClient().add(session.getId(), baos.toByteArray());
		Object ob = getMemcacheClient().get(session.getId());
		List<String> keyList = getKeyList();

	 * @return
	private List<String> getKeyList() {
		return keys;

	 * Simple instanc of the Memcache client and SockIOPool.
	 * @return memchacheclient
	private MemCachedClient getMemcacheClient() {
		if (memclient == null) {

			Integer[] weights = { 1 };
			// grab an instance of our connection pool
			SockIOPool pool = SockIOPool.getInstance();
			if (!pool.isInitialized()) {
				String[] serverlist = servers.toArray(new String[] {});
				// set the servers and the weights

				// set some basic pool settings
				// 5 initial, 5 min, and 250 max conns
				// and set the max idle time for a conn
				// to 6 hours
				pool.setMaxIdle(1000 * 60 * 60 * 6);

				// set the sleep for the maint thread
				// it will wake up every x seconds and
				// maintain the pool size

				// set some TCP settings
				// disable nagle
				// set the read timeout to 3 secs
				// and don't set a connect timeout

				// initialize the connection pool

			// lets set some compression on for the client
			// compress anything larger than 64k

			memclient.get().setCompressThreshold(64 * 1024);
		return memclient.get();

	public List<String> getServers() {
		return servers;

	public void setServers(String serverList) {
		StringTokenizer st = new StringTokenizer(serverList, ", ");
		while (st.hasMoreTokens()) {


The configuration for the context:

<Context path="/web" docBase="./deploy/web-0.0.1.war">
	<Manager className="org.apache.catalina.session.PersistentManager"
		<Store className="com.avc.hq.MemcachedStore"
			servers="" />


Thats all. The quite simple way :)

-avc (arkadiusz victor czarnik)

Categories: 16ms Tags:

The best Java Exception ever

October 10th, 2008 makii Comments off

A lot of thanks to Code To Joy for the best Java Exception I ever saw: JavaDoc of CME

Categories: Coding, Java, funny Tags:

Computer Spezialisten findet man in …

October 10th, 2008 makii 1 comment

Computer Spezialisten

Categories: funny, german Tags:

Klick dich nicht weg!

October 10th, 2008 makii Comments off

Ein schönes und wahres Bild was mir Manuel gerade zukommen hat lassen (via

Klick dich nicht weg!

Categories: Technology, german, office Tags:

Database book

October 9th, 2008 makii Comments off

bleiente pointed out this very nice book about databases. I’m sure it describes every issue you ever had with a database in a comprehensible way.

Categories: Technology, funny, office Tags:

in 5 min to Tomcat Cluster…

October 9th, 2008 AVC Comments off


This section describes how to setup a Tomcat 5.5 cluster with in-memory session replication and configure the cluster to use JK as the load balancing module.
Steps to Setup a Tomcat Cluster and Configure it for Load Balancing

1. Configure Tomcat application servers for load balancing
Edit TOMCAT_HOME/conf/server.xml. Locate the <Engine> element and add a jvmRoute attribute to it:

<Engine name="Catalina" defaultHost="localhost" jvmRoute="NODE_NAME">
... ...

The NODE_NAME must match the name that you will define in the JK configuration (for example “node1″ or “node2″).
2. Edit EP5_DEPLOY_DIR/WEB-INF/web.xml
Set the application as distributable in the web.xml descriptor. e.g.:

<?xml version="1.0"?>
<!-- ... -->

3. Configure session replication
Add the following lines to TOMCAT_HOME/conf/server.xml and (replacing SERVER_IP_ADDRESS with the IP address of your server).

<Host ......>
<Cluster className="org.apache.catalina.cluster.tcp.SimpleTcpCluster"
mcastDropTime="3000" />
tcpThreadCount="6" />
waitForAck="true" />
<Valve className="org.apache.catalina.cluster.tcp.ReplicationValve"
filter=".*\.gif;.*\.js;.*\.jpg;.*\.png;.*\.htm;.*\.html;.*\.css;.*\.txt;" />
<Deployer className="org.apache.catalina.cluster.deploy.FarmWarDeployer"
watchEnabled="false" />
<ClusterListener className="org.apache.catalina.cluster.session.ClusterSessionListener" />

Steps to Setup a Tomcat Cluster and Configure it for Load Balancing with database persisence of sessions

1. Configure Tomcat application servers for load balancing
Edit TOMCAT_HOME/conf/server.xml. Locate the <Engine> element and add a jvmRoute attribute:

<Engine name="Catalina" defaultHost="localhost" jvmRoute="{NODE_NAME}">
... ...

The NODE_NAME must match the name that you will define in the JK configuration (for example “epnode1″ or “epnode2″).
2. Create a table to store sessions
Choose a database server and create a table to store sessions.
For example, with MySQL the table can be created with the following SQL.

create database tomcat;
create table tomcat$sessions
id varchar(100) not null primary key,
app varchar(255),
valid char(1) not null,
maxinactive int not null,
lastaccess bigint,
data mediumblob

3. Configure Tomcat to store sessions in the session table
Configure the Tomcat context to store sessions into the session table.
For example, the connection to a MySQL table can be configured as follows.

<Manager className="org.apache.catalina.session.PersistentManager"
<Store className="org.apache.catalina.session.JDBCStore"
debug="99" />

gretz avc(arkadiusz v. czarnik)

Categories: 16ms Tags: