EXT3, EXT4, JFS, XFS Weekend Encounters

Sometimes I'm a gluten for punishment when it comes to technology. My self-inflicted punishment this weekend was spending time formatting and copying data using xfs, jfs, and ext4 filesystems under Linux.

It started out several days ago when I got the itch to move from ext3 to a different filesystem to test the performance. I've been through this before, but it had been a while. I was tempted to try ext4 right off the bat, but decided to try xfs. I ran xfs for several days, and I really liked it. However, in an effort to fix my sound card not living up to Fedora's 10 promise of glitch-free audio ( this is another story in and of itself ), I had to hard-reboot my computer and ended up with a 0-length file on an opened file. This is not unusual for an unclean shutdown of xfs, so I wasn't mad, but decided to try jfs. A few reboots later, and a lot of time sitting around waiting to backup/restore a 90+GB root partition, jfs was up an running on the root partition. No problems, but I then came across the ext3 options for "xfs-like and jfs-like" behaviour by adding data=writeback,nobh,commit=30 mount options. So, back to ext3 with those options, and I was impressed. No official benchmarks to post, but it felt good and I was back on an ext filesystem.

After running ext3 for a while, I realized Fedora Rawhide had moved from ext4dev ( the pre-release ) to ext4. Why not, I already had the data backed up, so...reboot, rsync, mkfs.ext4, and a cp and I was back up running ext4 with the "data=writeback,nobh,commit=30" mount options.

While these mount options are a little more risky on hard reboots, it appears the worst that should happen is stale data--not a 0 byte file like xfs was so kind to produce. I can live with old data, but corrupt data is where I draw the line.

So far, the ext4 is blazing fast. It's running over a software raid 0 config. On the first reboot, the raid device forced a fsck. I was very impressed the 150GB partition fsck finished in less than a minute--compared to the several minute fsck the ext3 partition took on it's initial boot.

ext4 is the filesystem of choice for me now.

GNOME is Back for me

I previously posted about KDE 4.1. While I enjoyed it's cool looks, I've found GNOME is currently just more productive for me. So, I find myself running GNOME at work and home. Choice is great, and I'm sure this won't be the last time I try out KDE.

KDE 4.1 Much Improved

I installed KDE 4.1 today on a few of my machines. I'm quite happy with it now, and I will be making the switch from GNOME back to KDE. KDE 4.0 was too buggy to work with. After a few crashes of KDE 4.0 within the first hour of installation, I went right back to GNOME 2.22.

GNOME is fine for the most part, though there were often times I wanted to customize something that I just couldn't do ( dual headed background limitations, running a separate screensaver process per head slamming the cpus, and lack of any customization in the newly, revamped gdm architecture come to mine ). But I digress. For me, KDE 4.1 is stable, looks great, and so far is not lacking any customizations I need. It took a few minutes of figuring out where the team is headed with Desktop folder views. I think they're way cool, and they help one keep a nice, organized desktop.

If you gave up on KDE 4.0 like I did, jump back on! KDE 4.1 shows the dedication of the KDE team to answering issues and pioneering the way for the Linux desktop.

Flex BlazeDS XML Parsing

I've received some great comments on my recent entry Simplified BlazeDS and JMS. A few people had some issues, and I wanted to clarify one thing I discovered early on, fixed, forgot, and then was reminded of as others encountered the same problem -- Flex BlazeDS xml parsing does not remove any spaces or linefeeds from the xml between the xml tags and the value. If, for instance, your xml formatter places line feeds between your xml tags and the containing text values, you will encounter problems.

Also I've set up an email at mmartinsoftware@comcast.net for those who wish to email me or want sample code emailed to them. I'll have to look for some hosting space to make it easier down the road.

OpenLDAP 2.4.9 Multi-Master Replication Stability Improved

I pulled in OpenLDAP 2.4.9 to re-visit some multi-master testing I had done on the previous version. 2.4.9 was a better experience for me than 2.4.8. I re-ran some tests of running two replicated servers on the same machine. I would continuously load in several hundred or thousand user records on one server, then delete them.

The stability is improved from 2.4.8. I have yet to have a server core on me--even after abruptly shutting done one or both servers during a batch load or delete.

My only issue now is that when performing a bulk load, if you interrupt the client during the load ( Control-c ldapadd ) the servers get out of sync. The server you directly attach to in order to load the records contains more records than the "replicated" server. Under most circumstances, this would not be a huge issue, but it does show an easy way for a client to get the servers out of sync.

With the 2.4.9 release of OpenLDAP, I would trust the multi-master synchronization enough now for use on production systems.

Simplified BlazeDS and JMS

I've been using Flex for some time now, and finally got around to trying out BlazeDS. What really peaked my interest was it's claim to publish and consume JMS messages from both topics and queues.

The one area in web development that I always struggle with is asynchronous messaging from the server to clients over HTTP. I'm pleased to announce that I got a simple application up and running.

The goal of this post is to share the example and lessons learned in order to save others some of the problems I ran into.

My project had a few main goals:

• Get a simple pub/sub example up and running
  
• Avoid using the "pre-configured" download. I wanted to get a project up and running "from scratch"
  
• Use my existing ActiveMQ broker running in it's own JVM
  
• Use my existing Tomcat install
  
• Use mxml as much as possible and avoid writing Actionscript
  
• Keep it simple to get a working example
  

Before I get into the example code, a few things I ran into:

• The BlazeDS documentation is good, but far from perfect. The messaging examples switch from mxml to actionscript, so it makes it a little difficult to piece things together. Also, it's not clear in the examples what many of the values point to--i.e. is that the JMS Topic name or the destination name???? I also found a few syntax problems in the examples which caused some "cut and paste" problems for me.
  
• A key piece I discovered after nothing was working at all, was the use of the "-services" flag to the mxmlc compiler. You have to compile your mxml file with the services file you plan to call.
  
• Don't rely on client side faults. Prior to finding out about the "-services" flag, I would call the send method in the client, but nothing happened--the faultHandler was never called on the client, and nothing appeared in the server logs. Once I compiled with the "-services" flag, things began to click.
  
• Make sure the JNDI names are correct. BlazeDS looks up the JMS ConnectionFactory and Topics via JNDI calls to Tomcat's JNDI. Make sure you specify the full JNDI name of the resource. i.e java:comp/env/jms/messageTopic
  

The example contains 5 main files:

1. A standard web.xml file with a BlazeDS servlet to handle the remote calls
   
2. A Tomcat context.xml file to add the JNDI values for the required JMS resources
   
3. A BlazeDS services-context.xml file to set up the services and channels
   
4. A BlazeDS messaging-config.xml that stores the messaging service(s).
   
5. A test.mxml file which is compiled into the Flex application.
   

The image to the right shows the file locations in the final WAR layout.

web.xml
The web.xml file is pretty basic. The main 2 things to point out are the HttpFlexSession listener and the MessageBrokerServlet. The servlet loads up you services, so it is passed the location of the services-config.xml file inside the WAR file.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN" "http://java.sun.com/dtd/web-app_2_3.dtd">
<web-app>
<display-name>BlazeDS</display-name>
<description>BlazeDS Application</description>

<!-- Http Flex Session attribute and binding listener support -->
<listener>
<listener-class>flex.messaging.HttpFlexSession</listener-class>
</listener>

<!-- MessageBroker Servlet -->
<servlet>
<servlet-name>MessageBrokerServlet</servlet-name>
<display-name>MessageBrokerServlet</display-name>
<servlet-class>flex.messaging.MessageBrokerServlet</servlet-class>
<init-param>
<param-name>services.configuration.file</param-name>
<param-value>/WEB-INF/flex/services-config.xml</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>MessageBrokerServlet</servlet-name>
<url-pattern>/messagebroker/*</url-pattern>
</servlet-mapping>
<welcome-file-list>
<welcome-file>index.html</welcome-file>
<welcome-file>index.htm</welcome-file>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>

context.xml
The context.xml file is for Tomcat. You can read more about it in the Tomcat documentation. The key take away is the "name" attribute is the JNDI name that has to match the jndi name used in the messaging-config.xml file.

<?xml version="1.0" encoding="UTF-8"?>
<Context path="/BlazeTest">
<Resource name="jms/flex/TopicConnectionFactory"
        type="org.apache.activemq.ActiveMQConnectionFactory"
        description="JMS Connection Factory"
        factory="org.apache.activemq.jndi.JNDIReferenceFactory"
        brokerURL="tcp://localhost:61616"
        brokerName="myBroker"/>
<Resource name="jms/messageTopic"
        type="org.apache.activemq.command.ActiveMQTopic"
        description="a simple topic"
        factory="org.apache.activemq.jndi.JNDIReferenceFactory"
        physicalName="messageTopic"/>
</Context>

services-config.xml
The services-config.xml file is used by BlazeDS. It is first used when you go to compile the mxml file. When you deploy the war file to Tomcat, this file is also loaded up by the MessageBrokerServlet.

During compilation, you pass it in like this using the relative path to it from your mxml file.

~/java_libraries/flex3/bin/mxmlc -services=WEB-INF/flex/services-config.xml test.mxml

My current file turns on logging which can help during resolve messaging problems like jndi resources not being found. This file loads in the messaging-config.xml file which is described below.

The channels determine how the client will talk to the server. The endpoint has to match the servlet-mapping url-pattern contained in the web.xml. Since the servlet is grabbing /messagebroker/* and my application is deployed under BlazeTest, the endpoint becomes:

http://localhost:8080/BlazeTest/messagebroker/amf

The "amf" on the end of the URL can be called anything--it's what distinguishes one channel url from another channel url. Here, I am only using one channel.

<?xml version="1.0" encoding="UTF-8"?>
<services-config>
<services>
<service-include file-path="messaging-config.xml" />
</services>
<security/>
<channels>
<channel-definition id="my-amf" class="mx.messaging.channels.AMFChannel">
<endpoint url="http://localhost:8080/BlazeTest/messagebroker/amf" class="flex.messaging.endpoints.AMFEndpoint"/>
</channel-definition>
</channels>
<logging>
<target class="flex.messaging.log.ConsoleTarget" level="Debug">
<properties>
 <prefix>[BlazeDS] </prefix>
 <includeDate>false</includeDate>
 <includeTime>false</includeTime>
 <includeLevel>false</includeLevel>
 <includeCategory>false</includeCategory>
</properties>
<filters>
 <pattern>Endpoint.*</pattern>
 <pattern>Service.*</pattern>
 <pattern>Configuration</pattern>
</filters>
</target>
</logging>
</services-config>

messaging-config.xml
This file stores the JMS services and tells BlazeDS where to get the JMS ConnectionFactory and Topics from the JNDI lookup. The part here that caused be a little problem was making sure the connection-factory and destination-jndi-name values had the correct JNDI name Tomcat expected. Also, note the destination id value. When you set up the consumer or producer in the mxml file, you don't tell it what Topic or Queue to connect to, you tell it what destination to connect to. This makes sense, since the mx:Producer and mx:Consumer attribute is called "destination", but it did throw me for a little loop.

<?xml version="1.0" encoding="UTF-8"?>
<service id="message-service" class="flex.messaging.services.MessageService">
<adapters>
<adapter-definition id="actionscript" class="flex.messaging.services.messaging.adapters.ActionScriptAdapter" default="true" />
<adapter-definition id="jms" class="flex.messaging.services.messaging.adapters.JMSAdapter"/>
</adapters>
<default-channels>
<channel ref="my-amf"/>
</default-channels>
<destination id="message-destination">
<properties>
<jms>
  <destination-type>Topic</destination-type>
  <message-type>javax.jms.TextMessage</message-type>
  <connection-factory>java:comp/env/jms/flex/TopicConnectionFactory</connection-factory>
  <destination-jndi-name>java:comp/env/jms/messageTopic</destination-jndi-name>
  <delivery-mode>NON_PERSISTENT</delivery-mode>
  <message-priority>DEFAULT_PRIORITY</message-priority>
  <acknowledge-mode>AUTO_ACKNOWLEDGE</acknowledge-mode>
  <initial-context-environment>
    <property>
      <name>Context.INITIAL_CONTEXT_FACTORY</name>
      <value>org.apache.activemq.jndi.ActiveMQInitialContextFactory</value>
    </property>
    <property>
      <name>Context.PROVIDER_URL</name>
      <value>tcp://localhost:61616</value>
    </property>
  </initial-context-environment>
</jms>
</properties>
<channels>
<channel ref="my-amf"/>
</channels>
<adapter ref="jms"/>
</destination>
</service>

test.mxml
The test.mxml is the final file. It's the GUI code. The file gets compiled into a swf file as I showed up above. My version uses mx:Producer and mx:Consumer mxml tags, though you can also instantiate these using Actionscript if you'd like. I prefer to write as little script as possible. The main key in this file was that I had to subscribe the consumer to it's destination before it would consume messages. Everything else is pretty simple, and you can see how easy it is to get a client sending and receiving messages to the server-side JMS broker over HTTP. This is why I like Flex!

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx='http://www.adobe.com/2006/mxml' xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance'
backgroundGradientColors="[0xcfe4ff, 0xffffff]" paddingTop="5" paddingLeft="5"
paddingRight="5" paddingBottom="0" applicationComplete="logon()">
<mx:Script>
<![CDATA[
        import mx.rpc.events.FaultEvent;
        import mx.messaging.*;
        import mx.messaging.messages.*;
        import mx.messaging.events.*;
         import mx.controls.Alert;

        private function messageHandler(event:MessageEvent):void {
          receiveTextArea.text = event.message.body  + "\n" + receiveTextArea.text;
        }
        private function acknowledgeHandler(event:MessageAckEvent):void{
        }
        private function faultHandler(event:MessageFaultEvent):void {
          Alert.show('Fault!', 'Alert Box', mx.controls.Alert.OK);
        }


        private function logon():void {
            consumer.subscribe();
         }

        private function sendMessage():void {
            var message:AsyncMessage = new AsyncMessage();
            message.body = sendTextArea.text;
            producer.send(message);
            sendTextArea.text="";
        }


    ]]>
</mx:Script>
<mx:Producer id="producer" destination="message-destination" acknowledge="acknowledgeHandler(event);" fault=" faultHandler(event)"/>
<mx:Consumer id="consumer" destination="message-destination" message="messageHandler(event)" acknowledge="acknowledgeHandler(event);" fault=" faultHandler(event)"/>
<mx:HBox>
<mx:TextInput id="sendTextArea"/>
<mx:Button label="Send" click="sendMessage();"/>
</mx:HBox>
<mx:TextArea id="receiveTextArea" width="50%" height="200"/>
</mx:Application>

The client app looks something like this:




In Conclusion, BlazeDS is an extremely simple way to use JMS with remote Flex clients over HTTP connections. The back-end configuation is somewhat complex, but mostly boilerplate and not too bad once you piece it together.

I haven't "stress" tested the messaging yet, or done very complex messaging to be able to say how robust and scalable it is, but so far, It does live up to it's claims. Best of all, I can now do asynchronous messaging to remote clients without writing code.

Java Self-Signed Certificates and Firefox 3 beta 5

A few weeks ago, I started having problems with Firefox 3 beta 5 and my self-signed certificates being used by some Tomcat servers. Though I could add the certificate as an exception, Firefox 3 beta 5 would not let me get in. I was using Java's keytool with the -genkeypair option to create the certificate.

I recently discovered a solution. keytool by default uses the DSA algorithm when generating the self-signed cert. Earlier versions of Firefox accepted these keys without problem. With Firefox 3 beta 5, using DSA doesn't work, but using RSA does. Passing "-keyalg RSA" when generating the self-signed certificate creates a cert the Firefox 3 beta 5 fully accepts.

I'm not sure if this is by Firefox design or not, but at least it's working for me.