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Below is a simple program that demonstrates how easy it is to use Space4J in a cluster. The main advantage of having a cluster, besides load balance, is the possibility of executing a snapshot without requiring the system to enter read-only mode. In that scenario, only the node executing the snapshot will enter read-only mode while the other nodes in the cluster will continue to operate like nothing was happening.
Space4J use simple sockets to perform the cluster replication, but future implementations may use JGroups or Java NIO.
The complete source code for the PhoneBookCluster application can be downloaded here: PhoneBookCluster.java. Make sure the space4j.jar is in your classpath before compiling and executing.
package org.space4j.examples.phonebook;
import org.space4j.Space4J;
import org.space4j.implementation.MasterSpace4J;
import org.space4j.implementation.SlaveSpace4J;
/**
* This is to show you how simple it is to make a Space4J cluster!
*
* To make a cluster, open up two shells (or DOS) and execute in the first:
*
* java org.space4j.demos.phonebook.PhoneBookCluster master
*
* and in the second:
*
* java org.space4j.demos.PhoneBookCluster slave 127.0.0.1
*
* You can also use two different machines. Just pass the master IP address to the slave instead of 127.0.0.1.
* IMPORTANT: If you use two different machines, you must have the main Space4J dir (space4j_db) mounted, so
* both machines can have access to it.
*/
public class PhoneBookCluster extends PhoneBookIndexing {
public PhoneBookCluster(Space4J space4j) throws Exception {
super(space4j);
}
static Space4J createSpace4J(String master, String master_ip) throws Exception {
Space4J space4j = null;
if (master.equals("-master")) {
space4j = new MasterSpace4J("PhoneBook");
} else if (master.equals("-slave")) {
if (master_ip != null) {
space4j = new SlaveSpace4J("PhoneBook", master_ip);
} else {
space4j = new SlaveSpace4J("PhoneBook", "127.0.0.1");
}
}
return space4j;
}
public static void main(String[] args) throws Exception {
if (args.length < 1 || args.length > 2) {
System.out.println(
"format: java PhoneBookCluster [-master|-slave] ");
return;
}
Space4J space4j = createSpace4J(args[0],
args.length > 1 ? args[1] : null);
PhoneBookCluster book = new PhoneBookCluster(space4j);
run(book);
}
}