Parallelism and Concurrency, Revisited

Existential Type

To my delight, I still get compliments on and criticisms of my post from three years ago (can it possibly be that long?) on parallelism and concurrency.  In that post I offered a “top down” argument to the effect that these are different abstractions with different goals: parallelism is about exploiting computational resources to maximize efficiency, concurrency is about non-deterministic composition of components in a system.  Parallelism never introduces bugs (the semantics is identical to the sequential execution), but concurrency could be said to be the mother lode of all bugs (the semantics of a component changes drastically, without careful provision, when composed concurrently with other components).  The two concepts just aren’t comparable, yet somehow the confusion between them persists.  (Not everyone agrees with me on this distinction, but neither have I seen a comparable analysis that shows them to be the same concept.  Most complaints seem to be about my use of the words…

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Code , Debug & Test Apache Pig Scripts using Eclipse on Windows

Abhijit Suresh Shingate


While developing a software, knowing how to debug the code is the most important part. It helps to solve any bugs in the code easily as well as helps us understand the internals of dependent framework code. It definitely applies to Apache Pig scripting. In this blog i will explain how to Code , Debug & Test Apache Pig Scripts using Eclipse on Windows.


  1. Install Eclipse Juno or above
  2. Install m2eclipse plugin
  3. Install JDK 1.6 or above
  4. Install Cygwin 1.7.5 or above
  5. <CYGWIN_HOME>/bin folder is added into PATH environment variable. CYGWIN_HOME is the installation directory of cygwin.


Before you start with following steps, make sure all prerequisites are met.

1. Start Eclipse

2. From Eclipse File menu, create a new project.

01 Createnewproject3. From New Project wizard, select Maven project and click on Next button.

02 createmavenproject

4. On New Maven Project screen, click on next button

03 createmavenproject2

5. Select “maven-archtype-quicktype”…

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Openstack Distributed Setup

Pravinchavan's Blog

This is guide for openstack distributed setup.

We are going to setup Controller machine, Dom0 with Xen hypervisor and Compute machine.

Here I am assuming my

Controller Machine IP as,

Compute machine IP as and

Hypervisor IP as

Please update the IPs as per your environment while following this document.

A) Setup Openstack Controller

Use : Ubuntu 12.04 server for controller setup.

Its good to use physical machine for Controller setup.

Use the Ubuntu Cloud Archive for Havana

  • Install the Ubuntu Cloud Archive for Havana
# apt-get install python-software-properties

# add-apt-repository cloud-archive:havana

  • Update the package database, upgrade your system, and reboot
# apt-get update && apt-get dist-upgrade

# reboot

Basic Operating System Configuration

  • MySQL DB Setup

Install mysql packages on controller

# apt-get install python-mysqldb mysql-server

  • Edit /etc/mysql/my.cnf and set the bind-address to the IP address of the controller
bind-address =
  • Restart mysql service
# service…

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It’s over 9000! Neo4j on WebSockets

Max De Marzi


In the last blog post we managed to run Neo4j at Ludicrous Speed over http using Undertow and get to about 8000 requests per second. If we needed more speed we can scale up the server or we can scale out to multiple servers by switching out the GraphDatabaseFactory and using the HighlyAvailableGraphDatabaseFactory class instead in Neo4j Enterprise Edition.

But can we go faster on a single server without new hardware? Well… yes, if we’re willing to drop http and switch to Web Sockets.

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