Move over to {proton:fever}

Migrated the blog to http://protonfever.com, henceforth please check the new blog for updates

iPhone SSH screenshots

It's been some time the iPhone jailbreak is available, and there are many posts available online. But I wanted to boast about my jailbroken version. Here are a few screenshots.

First the unix version; uname -a

After that I wanted to use some standard linux commands, but they were not available. When using Cydia, I saw some apt-get being executed; so tried it and installed 'top'
I started MobileSafari to check if was realtime, or it popped up in ms on this screen.

I was bored over the weekend and decided to jailbreak it, and was wondering; "What kept me away from it!!"

The e-Book progress

I was initially using google docs to write the e-book, but then was too lost in formatting the book, or proof reading it again and again. Also I could not update it using my phone, which is pretty much my hand held computer now. I was reading someone else's book online, when using the blog as an ebook sounded reasonable, so I've gone ahead and ported some chapters over to a new blog.

http://startupastartup.blogspot.com/

As of now the access is restricted, but if you want access, just comment to this post and I shall be glad to add you as a proof reader to my book.

DWR + Lazy Loading

Time immemorial, we are all aware about the famous lazy load exceptions in Hibernate. Using a detached object does not exactly hide us from the issue. We are using DWR in our application and found that when marshalling (or unmarshalling if you insist) a detached object to JSON, DWR was erratically trying to call a null (lazyly loaded) object, causing LazyLoadExceptions.

We did not want to use OpenSessionInViewFilter as it is evil (some day I'll post all the consolidated rantings as one). You can google and find a lot of info around it.

As a quick fix we did what one would first think of, "It's a demo, just eager load it!". Well the demo was over and now was the time to investigate a better solution, and we did find it.

It was no rocket science, the solution was available in front of us all along, we just did not look hard enough. When using DWR, there are BeanConverters available which are responsible for this marshalling process. There was one for Hiberante, called "hibernate3". http://directwebremoting.org/dwr/server/hibernate

The HibernateBeanConverter tries to avoid reading from un-initialized properties. (If you just want something that blindly reads everything then just use a plain BeanConverter).

Bingo, so when exporting a detached hibernate object to DWR, use type="hibernate3" and that should resolve the lazy load issues.

Cheap Memory

Finally upgraded myself to 4GB of memory on my personal laptop. The price was so cheap just could not resist it :)

Other reasons I was waiting for was better 64-bit Ubuntu support. I still need to reformat my machine. Some of the issues resolved by 64-bit which I was waiting on;

• Flash browser support (had to use a 32-bit script)
  
• Video codecs (works like a charm, even apple trailers work)
• Open Office (the icons & menu was all messed up)
• Support for my wi-fi atheros chipset (8.10 cured the problem, no more ndiswrapper)

Hopefully this weekend, I should be able to make a transition. Only if I had 64-bit Windows, what the heck, will wait for Windows 7.

TODO: Cleanup blog

I'm not able to get any good templates, I think I need to search more on the web, or come up with a good design myself...

Can I go back to Photoshop & CSS again?? Been quite some time now...

Hmm let me think..

By Contract or By Convention

Should we be using interfaces for everything and making everyone explicitly implement them or should we trust that everyone follows the same convention.

By Contract

For use cases, where a certain contracts needs to be followed, we should use interfaces, this allows easier testing and loose coupling of implementation, allowing us more flexibility to change the implementation at run time as asked for.

eg: UserService interface has a method fetchUser();

We can have two implementations for this service method, one using a DAO and other the WebService. Thus the implementation is loose and "the contract" is set to return a User.

By Convention

In certain cases, we cannot implement a contract, esp where the concerns span across multiple layers of the app. This is when we need to define convention over contract. AOP is the perfect use case where this needs to be strictly followed.

Let's consider the service methods which fetch information for displaying info to the front end. They need to have a specific security restriction associated with it, or a use case where we need to assign "READ_ONLY" rights to certain users for an object. In order to keep the code as decoupled as possible we use AOP, which apply concerns on these methods, without having actual references in the code.

For these concerns to be properly applied, we need to follow conventions.

eg: All DAOs should persist an object using the create() method only, that ways we can add a concern to block access to all create() methods for a group of user. If someone plans to "be different" and follow their own convention, like calling the method persist(), this can open up a huge security hole in the application. The AOP concern will skip "persist()" as it does not follow convention. Such issues will not be caught unless there is a proper code review performed on the code base, or we have really really strong test case.

If your module needs to follow a convention, which cannot be controlled using a contract, please document it, so as the team can follow is correctly.

2 DTO or not 2 DTO

Since the new project began I've been think about this over and over again reading as many posts and taking ideas from different posts and blogs. The more I read, the less I knew. Below is a collection of few links I've come across which have some conclusive and non-conclusive decisions/arguments, some of these post lean towards POJO's and some towards DTO. Frankly I was not been able to convince myself on what to use. (Leaning more towards POJO's as detached objects).

http://forum.springframework.org/archive/index.php/t-27716.html
http://forum.springframework.org/showthread.php?t=11338
http://forum.springframework.org/showthread.php?t=9810

http://www.hibernate.org/124.html

http://api.blogs.com/the_catch_blog/2005/05/protecting_the_.html
http://hookom.blogspot.com/2004/12/corporate-developer.html

Here is a small tutorial talking about how to develop using POJO's. Makes you think the non-EJB2 way. (Reading this is strongly recommended)
Part 1 - http://www.developer.com/java/ejb/article.php/3590731
Part 2 - http://www.developer.com/java/ejb/article.php/3592341
Part 3 - http://www.developer.com/java/ejb/article.php/3594121

Since EJB3 is more revolutionary and uses POJO's unlike remoting in EJB2, here is a link from the sun java forums
http://forums.sun.com/thread.jspa?threadID=5302559

I strongly recommend everyone to read these articles before choosing. My brains had been deep fried already reading these before trying to reach any conclusion. I wanted some other heads to think about these issues and post in their opinions.

Some points where I played the devil's advocate and jotted my concerns with arguments before we said 'I do' to DTO or POJO.
ProDTO: DTO will shield the UI if there are any model changes
Argument: Either ways we'll have to modify the DTO, the marshaller/unmarshaller to propagate these changes from the POJO to DTO. DTO does not eliminate the problem completely, but obfuscates or hides it.

ProDTO: Our service layer shall talk to various 'services' webUI or web Service or RMI or Star Trek, so we need DTOs to provide loose coupling and don't want the service to expose the domain object directly.
Argument: We will use XML (WSDL or SOAP or RestFUL or ) for data transfer, which will involve marshalling/unmarshalling of the XML to DTO and then POJO & vice-versa, any changes will again have to propagated. through all the layers. We are just exposing the POJO to the XML transformer, not the DAO calls. The POJO by itself cannot persist if in a detached state. Unless we have a usecase of just exposing half the object to the webservice (do we have a usecase?)

ProPOJO: Less effort, lean and clean design, any changes will propagate at multiple places and will provide less points of transformation errors.
Argument: The inner implementation of the POJO with the Data model needs to be changed, but the view/web service does not have to change the implementation. We have to make the changes in these layers even if we don't have to, there by adding more work and complexity.

ProPOJO: No over head of transforming POJO to DTO and vice-versa. Less memory consumption.
Argument: It's a good practice to separate your business objects and data objects, provides better decoupling.

Anti-POJO: Handling Lazy Initialization of hierarchical objects, no openSessionInView Filter for ExtJS.
Anti-DTO: Locking of objects for optimistic locking. DTO's are not aware of the revision.

Conclusion: Use POJOs as detached objects where basic CRUD calls are required and for fetching objects with minimum hierarchy, but if you need to fetch loads of info from different tables with a very small subset of columns from each, then use HQL + DTO

Select new com.vtech.model.dto.CompanyEmployee(bla bla bla);

You've got hacked :)

Yup since I opened up the ssh ports, once a day someone tries to get into the system. Here a small piece of log,
Oct 13 17:19:07 *******-server sshd[7250]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=58.117.255.223 user=nobody
Oct 13 17:19:09 *******-server sshd[7250]: Failed password for nobody from 58.117.255.223 port 35131 ssh2
Oct 13 17:19:17 *******-server sshd[7255]: Invalid user patrick from 58.117.255.223
Oct 13 17:19:17 *******-server sshd[7255]: pam_unix(sshd:auth): check pass; user unknown
Oct 13 17:19:17 *******-server sshd[7255]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=58.117.255.223
Oct 13 17:19:19 *******-server sshd[7255]: Failed password for invalid user patrick from 58.117.255.223 port 35703 ssh2
Oct 13 17:23:50 *******-server sshd[7325]: Invalid user jane from 58.117.255.223
Oct 13 17:23:50 *******-server sshd[7325]: pam_unix(sshd:auth): check pass; user unknown
Oct 13 17:23:50 *******-server sshd[7325]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=58.117.255.223
Oct 13 17:23:52 *******-server sshd[7325]: Failed password for invalid user jane from 58.117.255.223 port 52794 ssh2
Oct 13 17:23:59 *******-server sshd[7327]: Invalid user pamela from 58.117.255.223
Oct 13 17:23:59 *******-server sshd[7327]: pam_unix(sshd:auth): check pass; user unknown
Oct 13 17:23:59 *******-server sshd[7327]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=58.117.255.223
The address belongs to some kid in China (Beijing Education Information Network). The box has been safe so far.

Nobel Gases

Finally after successfully setting up OpenVPN with Linux server and XP/Ubuntu clients (Vista is evil), we decided to create the final network, but were stalled with the general problem of names (wonder what will I do when I have to name my kids!!). Looked around for tips and there is an RFC on it RFC 1178 which gives a few tips for names.

Without much ado the names helium, neon, argon, krypton clicked. Nobel Gases I say...

Book progress

I've finished the first chapter and have been able to rope in a few friends help me proof read and correct me along the way. I had never thought writing a book would be so much fun, but there is a lot of thought process also put in to make it as simple yet professional for anyone and everyone to understand.

There are many references from wikipedia for definitions of certain terms and terminologies. For those who don't trust wikipedia can search up their favourite reliable resources for further explanation and review.

Another interesting problem I'm facing as I go ahead is, how much detailed should the explanation be. What is the level of assumption I should consider while explaining a topic. Hopefully my friends will be able to point that out, if you are interested to participate in the proof reading, just drop me an email and I'll be glad to send you an invite.

My first E-Book: Kick Start a software start-up

Ok after all the configuration and working of the VM server with 4 virtual machines, I found it too much info to blog (lazy me..) with all the steps and configuration (I have some 3 posts still as draft yet to be published). There were some random thoughts on how this process and infrastructure can be used by others (start-ups or low budgets) for thier benefit.

Since most of the blog postings are enlightenments that occured to time once in a while, I've decided to consolidate all this information and jott them down like a step-by-step guide on how can we use the VM infrastructure for small shops or small projects in large shops. The table of contents for this book will look something like this.

Table of Contents

• Preface
• Who should read this book
• What are the technologies we'll cover
• Introduction
• Analyzing & Building the server
• Software selection.
• RAID & LVM
  
• Setup & Configure your first VM
• VPN Applicance
• Creating more Appliances I: Webserver, Database
• Creating more Applicanes II: Version Control, Continious Integration Servers
• Timed VNC sessions (iTalc or vncthumbnailviewer)
• Appendix A: Configure your Linksys router with DDNS

If you have anything else you would like to consider let me know if practically possible I'll try to include it into the book. I hope to get the book out in 2-3 months (provided I can give it one hour a day). People volunteering for proof-reading are most welcome.

CollectionUtils (apache commons) Bad Boy....

We had a problem at work today, where we need to find the difference between two collections and remove the uncommon ones from the first one and add the uncommon ones from the first to the second.

This is related to hibernate add-remove-update for collections. Read here about it

Set A = {R, G, B}
Set Z = {R, G, Y}

Final Set to the DB is = {R, G, Y}, well looks simple so we just send the second set Z, yeah but the catch is it needs to maintain the instance of A and finally send back A to the hibernate layer again, so all the manipulations happen on it.

Mathematically solving the problem, we need an intersection of A & Z {R, G} and a union of the relative complement of A & Z {R, G } + {Y} = {R, G , Y}

Using Java we can solve this using three approaches.

• For Loop
• CollectionUtils
• JDK collections native (1.6)

For Loop

private static void forLoop(List<Set<String>> all) {
Set db = all.get(0);
Set web = all.get(1);

Set tempCollection = new HashSet<String>();
tempCollection.addAll(db);

for (String t : tempCollection) {
if (!web.contains(t)) {
db.remove(t);
}
}

for (String t : web) {
if (!tempCollection.contains(t)) {
db.add(t);
}
}
} 

CollectionUtils

private static void collectionUtils(List<Set><String>> all) {
Set db = all.get(0);
Set web = all.get(1);

CollectionUtils.retainAll(web, db);
db.addAll(web);
}

JDK Collection Native

private static void jdkNative(List<Set><String>> all) {
Set db = all.get(0);
Set web = all.get(1);

db.retainAll(web);
db.addAll(web);
}

Now we ran a performance test on both, and were shocked to see the results.

• forLoop -18 ms
  
• collectionUtils -72 ms
  
• jdkNative -5 ms

This is what the web and db collection were made up of.

Create Collections

    private static List<Set<String>> createCollections() {
 List<Set<String>> all = new ArrayList<Set<String>>();

 Set<String> db = new HashSet<String>();
 Set<String> web = new HashSet<String>();
 for (int i = 0; i < 10000; i++) {
   db.add(String.valueOf(i));
 }

 for (int i = 5000; i < 15000; i++) {
   web.add(String.valueOf(i));
 }

 all.add(db);
 all.add(web);

 return all;
}

and the main method

  public static void main(String[] args) {
 long start = 0;
 long end = 0;

 List<Set<String>> all = createCollections();

 start = new Date().getTime();
 forLoop(all);
 end = new Date().getTime();
 System.out.println("TIME BY forLoop " + (end - start));

 start = new Date().getTime();
 jdkNative(all);
 end = new Date().getTime();
 System.out.println("TIME BY jdkNative " + (end - start));

 start = new Date().getTime();
 collectionUtils(all);
 end = new Date().getTime();
 System.out.println("TIME BY collectionUtils " + (end - start));

}

So avoid using the CollectionUtils. See what is more important, cleaner code or faster code ;)

iPhone & CFA

I've enrolled myself for the Level I CFA exam in December '08. Studying on and off, depending on the schedule and time availability. Off late I stumbled upon SenFinance an interesting site full of Accounting and Quantitative tutorials for CFA Level I.

I downloaded them all and wanted to view them on my way to work (a 20 minute train travel is good to study). So I got my hands on SUPER® which is an amazing software to convert any one video or auto file to another format. Now I finally have the tutorials in mp4 format and can study on my way to work!

Setting up a PHP development environment on your local system

This is an old post I had written on google docs, before VMware Server was free for the general user. Thought could be still more relevant to the general developer for testing in Linux envoirment. VMPlayer I beleive is lighter than VMware Server.

There are 2 stages of setting up the development & testing environment for yourself. The preferred work environment is Linux. If you already on Linux then you can safely skip Stage I, you can directly proceed to Stage II, also if you have Linux already installed, just cross check if you have the LAMP (Linux + Apache + MySQL + PHP) server installed.

Pre Installation Software Download Links

• http://www.vmware.com/download/player/ [VMPlayer]
• http://www.ubuntu.com/getubuntu/download [Ubuntu]

STAGE I: Setting up Ubuntu on VMWare.

• Download Ubuntu/Xubuntu/Kubuntu Desktop edition ISO, what ever you like... all the same just different filemanagers (Gnome/Xfe/KDE resp.). If you are comfortable with command line, then you can also install the Server edition with no XWindows and only commandline.
• Download and install VMPlayer for your system.
• Download qemu for your operating system and extract in any directory you like.
• Open your commandline to go ahead to bin folder of qemu and type

qemu-img create -f vmdk ubuntu.vmdk 3G

• Here we are creating a 3GB, virtual hard drive in VMWare format. This file will now act as our hard drive for VMWare to install an OS on it. The name of the file is ubuntu.vmdk, you can name it what ever you wish to.
• Now the main vmx file (The VMWare configuration file). change the highlighted paths as per your system.
  

 #!/usr/bin/vmware
config.version = "8"
virtualHW.version = "4"
ide0:0.present = "TRUE"
ide0:0.filename = "ubuntu.vmdk"
# The amount of RAM you want to allot to the Operating system. For Desktop use 512 and server just 256.
memsize = "512"
MemAllowAutoScaleDown = "FALSE"
ide1:0.present = "TRUE"

#ide1:0.fileName = "auto detect"
#ide1:0.deviceType = "cdrom-raw"

ide1:0.fileName = "ubuntu-7.04-server-i386.iso"
ide1:0.deviceType = "cdrom-image"

ide1:0.autodetect = "TRUE"
floppy0.present = "FALSE"
ethernet0.present = "TRUE"
usb.present = "TRUE"
sound.present = "TRUE"
displayName = "Ubuntu LAMP Server"
guestOS = "ubuntu"
nvram = "ubuntu-server-three.nvram"
MemTrimRate = "-1"

ide0:0.redo = ""
ethernet0.addressType = "generated"
uuid.location = "56 4d ce 99 e0 d2 2b bf-73 47 ac 62 65 13 57 86"
uuid.bios = "56 4d ce 99 e0 d2 2b bf-73 47 ac 62 65 13 57 86"

tools.syncTime = "TRUE"
ide1:0.startConnected = "TRUE"

uuid.action = "create"

checkpoint.vmState = "ubuntu-lamp-server.vmss"

isolation.tools.hgfs.disable = "TRUE"
virtualHW.productCompatibility = "hosted"
tools.upgrade.policy = "manual"

tools.remindInstall = "TRUE"

usb.autoConnect.device0 = ""

• After setting all the paths correctly, if you have VMPlayer installed, just save the vmx file, (call it ubuntu.vmx) and double click on the file.
• If all the paths are set correctly, the VMPlayer will boot up the virtual drive and show the ubuntu installation menu. This is easier than windows a million times.
• At the end of the installation (server or desktop) the process will ask you, if you want to install LAMP server. Select it and let it install the LAMP server.
• Reboot the system, and you are good to go. You have successfully installed Ubuntu on VMWare.

STAGE II: Check the configuration setup of Apache/MySQL/PHP

Now we'll check if PHP and Apache have been successfully installed on your system. Go the /var/www folder, you should be seeing a apache2-default folder out there. If you see these then apache seems to be installed. Just open the browser and type http://localhost you should be able to see the apache-default folder over there. If you a receive a page not found then apache is not running or installed properly.

If things look good, next stage is to check PHP installation. Create a file named index.php and type the following there.

 <?php phpinfo(); ?> 

Just refresh the localhost (place the file in /var/www) That should give you loads of PHP info on the screen in blue, purple and a huge table. If that happens you are good to go!!! Else something is wrong!!!.

MySQL Check
Open the command line and type

mysql -uroot

If it opens up with a mysql> prompt then it's good else something is wrong. Your mysql password is blank.

If all sounds good, now go to Stage III

STAGE III: Applications to setup.

Download

• JOOMLA
• WORDPRESS

Extract them to the /var/www folders and access them using http://localhost/joomla and http://localhost/wordpress respectively if you extracting them to the folders on these names.

How to go about setting them, start the index.php or read the readme file and you should be good to go.

The demise of MyGadgetBuilder

Hello all, my previous blog, MyGadgetBuilder.com has been officially shut down. I'll not be renewing the domain name any more, so some one can go ahead and claim it. It was a nice learning experience. Being a developer with some design skills, putting up the site was a piece of cake, but getting people to post on the site was kind of painful.

People had issues with copyright, data protection and all kinds of issues. Also things/people change as time passes by, everyone gets busy with their own profession and has little time for off-track exploration for their old love (electronics). I don't blame them, priorities do change; but took me some time to realize :) better late than never.

Well all for good. Hence forth MGB will point to this blog (till end of subscription life). Instead visit Instructables a nice site, which already existed on the lines of the world I was planning to build.

Cloud Computing on VMWare or Xen

What is Cloud Computing (CC)?
A lot has already been said and blogged about cloud computing. Just to give you a one liner about it;

It's the availability of system resources to allow scalability of the system as and when required by the application.

As and when required?
Consider an example of a build server running in our VM environment, now this server during it's peak instrumentation of code and all kinds of code analysis requires the power of a quad core machine with 4GB RAM, so when you perform your hardware requirement analysis for this server, you consider all these factors and build a VM fulfilling these requirements.

Over the period of time your system usage reports show a small spike in system resource usage every 3-4 hours (every commit build) and a peak spike for 2-2.5 hours every 24 hours (nightly builds), the remaining time the system is pretty much idle doing nothing, eating up precious RAM allocation and number of CPUs dedicated.

Now if we push this setup in a CC environment, the system will use bare minimum resources when idle and grab all the possible resources from the cluster, during peak cycles. This allows us to leverage the un-utilized system resources, during non-peak cycles.

VMWare has DRS - Distributed Resource Scheduler, which helps the VMs attain similar to cloud status to dynamically allocate the resources.

Now Xen also has something similar, but then is it available for a small start-up (read free)? Yes, Nimbus@UC is something we can look at, will try digging in more into it and see what we can achieve out of it. So let us see how we can leverage the existing hardware to allow maximum virtual resource utilization.

Update: Read this article http://highscalability.com/eucalyptus-build-your-own-private-ec2-cloud

Virtualization: The Practical Implementation - I

I'm helping my friend Nitin at his firm Star4ce Technologies put up a virtualization server as their in-house development environment. To begin with we went ahead and ordered some hardware from newegg.

Here is a brief on the hardware we've picked;

• Intel Core 2 Quad Q9300 Yorkfield 2.5GHz LGA 775 95W Quad-Core Processor
• ASUS P5K-E LGA 775 Intel P35 ATX Intel Motherboard
• (5) Seagate Barracuda 7200.11 ST3500320AS 500GB 7200 RPM SATA 3.0Gb/s Hard Drive
• (2) CORSAIR 4GB (2 x 2GB) 240-Pin DDR2 800 (PC2 6400) SDRAM Dual Channel
• LITE-ON 20X DVD±R DVD Burner with LightScribe SATA
• Antec 850W ATX12V / EPS12V Power Supply
• Antec P182 Gun Metal Black 0.8mm cold rolled steel ATX Mid Tower Computer Case
• ZOTAC GeForce 7300GT 256MB 128-bit GDDR2 PCI Express x16
• Logitech USB + PS/2 Cordless Standard Desktop EX110 Mouse Included

Now the bill fits to around $1,500.00 as of the day this article was written. Hopefully by next week we shall receive the components and we shall go ahead and assemble the system.

A few after thoughts about the hardware choices

Intel Core 2 Quad Q9300
45nm consumes less power compared to predecessors and can be over clocked to 3.2GHz.

ASUS P5K-E
It's not a high end server, but can be used for a low end server. We did see a few other motherboards but opted for this, as they had SLI and were more geared towards being gaming PC's.

Why no Server Motherboards
This is an interesting find we dug into, we decided to hit the server motherboards for the system, as they supported 32GB of RAM quite easily as compared to the 8GB max of the above mentioned. The price was not that different approx $150.00 higher (with dual processors -physical) but it had FB-RAM which took the toll on the price of the system. 4GB on FB-RAM goes to approx $250.00 to $550.00 for 8GB. Yes now that's a whopping high number we are talking about.

So we are back to reality with a lower end system (recall the first article) it was aimed towards start-ups and low budget development teams.

Seagate Barracuda 7200.11 ST3500320AS
32MB cache, and I trust Seagate. 5 pieces: 1- OS and 4- RAID 01

CORSAIR 4GB (2 x 2GB) 240-Pin DDR2 800
Nice & reliable.

ZOTAC GeForce 7300GT 256MB
There was no onboard video, this was the lowest and best

So we wait and watch for the parts to arrive. I'll be posting in intermittently the progress, issues & accomplishments along the way.

UPDATE: The shipping was quick, the parts should be arriving today afternoon.

DATETIME vs TIMESTAMP vs DATE & TIME - II

Ok now the test are run and the results are out, I know we are all excited to know them, and I'm equally eager to print them too!!

The test did a simple select * from the tables.

  public void fetchAll() throws Exception {
  String SQL1 = "SELECT * FROM dateandtime";
  String SQL2 = "SELECT * FROM datetime";
  String SQL3 = "SELECT * FROM timestamps";

  long start = 0;
  long end = 0;

  System.out.println("ONE");
  start = new Date().getTime();
  selectQuery(SQL1);
  end = new Date().getTime();
  System.out.println(" SQL 1 - dateandtime " + (end - start));

  System.out.println("TWO");
  start = new Date().getTime();
  selectQuery(SQL2);
  end = new Date().getTime();
  System.out.println(" SQL 2 - datetime " + (end - start));

  System.out.println("THREE");
  start = new Date().getTime();
  selectQuery(SQL3);
  end = new Date().getTime();
  System.out.println(" SQL 3 - timestamps " + (end - start));
}

The time to fetch kept on reducing with every subsequent calls.

 SQL 1 - dateandtime 4526 ms
SQL 2 - datetime 2852 ms
SQL 3 - timestamps 3577 ms

SQL 1 - dateandtime 4168 ms
SQL 2 - datetime 2467 ms
SQL 3 - timestamps 3073 ms

SQL 1 - dateandtime 4080 ms
SQL 2 - datetime 2346 ms
SQL 3 - timestamps 3130 ms

SQL 1 - dateandtime 3949 ms
SQL 2 - datetime 2419 ms
SQL 3 - timestamps 3043 ms 

So looks like DATETIME wins in fetching speed.

Duplicate file finder

Disk space is cheap, starting from a 1.2GB hard drive from my first computer to a "spare" 500GB external hard drive, cheap data storage has come a long way. I click a lot of photographs ever since I got my first digital camera, and I store a lot of these photos too (locally), now since 2006 I have over 201,608 photos and some videos. My camera photo number counter has reset twice!!

A few days back I decided to hand over my drive to my brother, since he was leaving soon, I dumped all the stuff on my two laptops, and forgot about them. Of late my wife asked me to pick up good nice pics so we can print them. That's when I realized I had a lot of duplicate photos, now the simplest idea was to find the duplicate file names and delete them, but that was not possible, since I had already reset the counter so I technically had 3 files with the same name and atleast 10,000 of them!!

MD5 to the rescue. Since all the photos and movies are binary files, MD5 seemed ideal to me...

MD5 digests have been widely used in the software world to provide some assurance that a transferred file has arrived intact. For example, file servers often provide a pre-computed MD5 checksum for the files, so that a user can compare the checksum of the downloaded file to it.

So I started my eclipse and churned out a program to scan my HDD and compare MD5 keys and find all duplicates.

The method below generates the MD5 checksum for any file

  private static String generateMD5(String path) throws IOException {
 MessageDigest digest;
 InputStream is = null;
 try {
   digest = MessageDigest.getInstance("MD5");
   is = new FileInputStream(new File(path));
   byte[] buffer = new byte[8192];
   int read = 0;

   while((read = is.read(buffer)) > 0) {
     digest.update(buffer, 0, read);
   }
   byte[] md5sum = digest.digest();
   BigInteger bigInt = new BigInteger(1, md5sum);
   return bigInt.toString(16);
 } catch(NoSuchAlgorithmException e) {
   e.printStackTrace();
 } catch(FileNotFoundException e) {
   e.printStackTrace();
 } catch(IOException e) {
   e.printStackTrace();
 } finally {
   is.close();
 }
 return null;
}

Then go ahead and get a list of all the files on your system

missed the code

And finally run the main method.

public static void main(String[] args) throws Exception {
 List filePaths = new ArrayList();
 File file = new File("/home/varun/workbench/duplicates.csv");
 FileWriter fw = new FileWriter(file);
 SortedMap duplicates = new TreeMap();
 filePaths = generateFileMap("/mnt/datastorage/photos", filePaths);
 for(String path : filePaths) {
   String hash = generateMD5(path);
   if(duplicates.containsKey(hash)) {
     fw.write(path + "," + duplicates.get(hash) + "\n");
   } else {
     duplicates.put(hash, path);
   }
 }
}

So go ahead and run this, you can also extend it to generate a list of any kind of duplicate files. Average file size is 1.5 - 2.0 MB

The output file when viewed on Open Office, Google Docs or Excel looks like this

This is how the output looks like this. It shows you which file a duplicate of which other file.

/mnt/datastorage/Photos/2008/Photos/Halloween NYC 2007/DSC01958.JPG /mnt/datastorage/Photos/2008/Photos/SORT ME/DSC01958.JPG
/mnt/datastorage/Photos/2008/Photos/Halloween NYC 2007/DSC01959.JPG /mnt/datastorage/Photos/2008/Photos/SORT ME/DSC01959.JPG
/mnt/datastorage/Photos/2008/Photos/Halloween NYC 2007/DSC01960.JPG /mnt/datastorage/Photos/2008/Photos/SORT ME/DSC01960.JPG

UPDATE: Ran the program with SHA algorithm also and here are the comparison times.

• Time for MD5 858,953ms (14.31 minutes)
  
• Time for SHA 1,191,656ms (19.80 minutes)
  

Bibliography

• http://en.wikipedia.org/wiki/MD5#Applications
• http://en.wikipedia.org/wiki/Md5sum