Ubuntu - Install Oracle JDK

Yes, there are also PPA, and etc...  But I wanted to write it down once for me...

Install the JDK

• Download the 32bit or 64bit Linux "compressed binary file" - it has a ".tar.gz" file extension i.e. "[java-version]-i586.tar.gz" for 32bit and "[java-version]-x64.tar.gz" for 64bit
• Uncompress it
  tar -xvf jdk-7u17-i586.tar.gz (32bit)
  tar -xvf jdk-7u17-linux-x64.tar.gz (64bit)

JDK 7 package is extracted into ./jdk1.7.0_17 directory. N.B. check carefully this folder name since Oracle seem to change this occasionally.

• Now move the JDK 7 directory to /usr/lib

sudo mkdir -p /usr/lib/jvm
sudo mv ./jdk.1.7.0_17 /usr/lib/jvm/oracle_jdk7

• Run

sudo update-alternatives --install "/usr/bin/java" "java" "/usr/lib/jvm/oracle_jdk7/bin/java" 1
sudo update-alternatives --install "/usr/bin/javac" "javac" "/usr/lib/jvm/oracle_jdk7/bin/javac" 1
sudo update-alternatives --install "/usr/bin/javaws" "javaws" "/usr/lib/jvm/oracle_jdk7/bin/javaws" 1

• Correct the permissions of the executables:

sudo chmod a+x /usr/bin/java 
sudo chmod a+x /usr/bin/javac 
sudo chmod a+x /usr/bin/javaws

N.B. remember - Java JDK has many more executables that you can similarly install as above.java, javac, javaws are probably the most frequently required.

This answer lists the other executables available.

• Run

sudo update-alternatives --config java

You will see output similar one below - choose the number matching oracle_jdk7 - for example 3 in this list:

$sudo update-alternatives --config java
There are 3 choices for the alternative java (providing /usr/bin/java).

Selection Path Priority Status
————————————————————
* 0 /usr/lib/jvm/java-6-openjdk/jre/bin/java 1061 auto mode
1 /usr/lib/jvm/java-6-openjdk/jre/bin/java 1061 manual mode
2 /usr/lib/jvm/java-6-sun/jre/bin/java 63 manual mode
3 /usr/lib/jvm/oracle_jdk7/jre/bin/java 3 manual mode

Press enter to keep the current choice[*], or type selection number: 3
update-alternatives: using /usr/lib/jvm/oracle_jdk7/jre/bin/java to provide /usr/bin/java (java) in manual mode.

Check the version of you new JDK 7 installation:

java -version

java version “1.7.0”
Java(TM) SE Runtime Environment (build 1.7.0_17-b02)
Java HotSpot(TM) Client VM (build 23.7-b01, mixed mode) 

Repeat the above for:

sudo update-alternatives --config javac
sudo update-alternatives --config javaws

Enable mozilla firefox plugin:

32 bit:
ln -s /usr/lib/jvm/oracle_jdk7/jre/lib/i386/libnpjp2.so ~/.mozilla/plugins/

64 bit:
ln -s /usr/lib/jvm/oracle_jdk7/jre/lib/amd64/libnpjp2.so ~/.mozilla/plugins/

N.B. you can link the plugin (libnpjp2.so) to /usr/lib/firefox/plugins/ for a system wide installation

Software and scalability: It is all a numbers game.

A fascinating talk by Martin Thompson on making scalable software:

It's all a numbers game -- the dirty little secret of scalable systems by Martin Thompson

My highlights from the talk...

At a high level:

• Be simple
• Share Nothing Architecture
• Profile the code once a week.
• Separate reads from writes
• Know the platform
• Use cache oblivious algorithms

From a pattern perspective:

• Use the "Single Writer Principle": Any item of data, or resource, is only mutated by a single writer/thread.  It is OK if multiple threads, or other execution contexts, read the same data. CPUs can broadcast read only copies of data to other cores via the cache coherency sub-system. This has a cost but it scales very well.
• Disruptor vs queues: See the LMAX project on GitHub (http://lmax-exchange.github.io/disruptor/). Associated technical paper http://disruptor.googlecode.com/files/Disruptor-1.0.pdf.
• The "Curse of Logging": Most common Java Logging libraries take way too many CPU cycles from the application (Log4j, JUL, Logback, etc.). 
• Command Query Responsibility Segregation (CQRS):  Split the conceptual model into separate models for update and display.  This refers to as Command and Query respectively following the vocabulary of CommandQuerySeparation. 

Read Martin's blog.