Ankit Jain » Tutorial/Links

Handling Data in Mega Scale Systems

Ankit — Fri, 20 Nov 2009 11:18:08 +0000

Vineet Gupta (from Directi) touches some practical aspects of scaling web-applications. He talks about scaling app-servers, database-servers, alternatives of RDBMS, handling replication and transactional behavior. Thought the presentation is big, it touches all major aspects of scaling and gives broader insight. Check out yourself…

Thanks Vineet !

Linear Hashing

Ankit — Mon, 22 Sep 2008 09:31:23 +0000

Hash table is a data structure that associates keys with values. To know more about liner hashing refer Wikipedia. Here are main points that summarizes linear hashing.

Full buckets are not necessarily split
Buckets split are not necessarily full
Every bucket will be split sooner or later and so all Overflows will be reclaimed and rehashed.
Split pointer s decides which bucket to split
- s is independent to overflowing bucket
- At level i, s is between 0 and 2ⁱ
- s is incremented and if at end, is reset to 0.

h_i (k)= h(k) mod(2ⁱ n)
h_i+1 doubles the range of h_i

Insertion and Overflow condition

Algorithm for inserting ‘k’:

1. b = h0(k)

2. if b < split-pointer then

3. b = h1(k)

Searching in the hash table for ‘k’:

1. b = h0(k)

2. if b < split-pointer then

3. b = h1(k)

4. read bucket b and search there

Example:

In the following M=3 (initial # of buckets)
Each bucket has 2 keys. One extra key for overflow.
s is a pointer, pointing to the split location. This is the place where next split should take place.
Insert Order: 1,7,3,8,12,4,11,2,10,13

After insertion till 12:

When 4 inserted overflow occurred. So we split the bucket (no matter it is full or partially empty). And increment pointer.

So we split bucket 0 and rehashed all keys in it. Placed 3 to new bucket as (3 mod 6 = 3 ) and (12 mod 6 = 0 ). Then 11 and 2 are inserted. And now overflow. s is pointing to bucket 1, hence split bucket 1 by re- hashing it.

After split:

Insertion of 10 and 13: as (10 mod 3 = 1) and bucket 1 < s, we need to hash 10 again using h1(10) = 10 mod 6 = 4th bucket.

When 13 is inserted same process is done, but it end up to the same bucket. But here is an overflow, we need to split 2nd bucket.

Here is the final hash table.

s is moved to the top again as one cycle is completed. Now s will travel from 0 to 5th bucket, then 0 to 12, etc;

Webservices PowerPoint Presentation

Ankit — Sat, 06 Jan 2007 13:20:20 +0000

My presentation on WebServices Basics is available for download to the *valuable visitors* of my blog. Here is the content:

Web services – Definition: A web service is a collection of protocols and standards used for exchanging data between applications or systems.
Characteristics
Demo: Writing a simple WebService in Visual Studio 2005 & Consuming WebServices
Technologies: XML (eXtensible Markup Language), SOAP (Simple Object Access Protocol), WSDL (Web services description language), UDDI (universal description, discovery, and integration)
SOAP: SOAP is an open protocol specification defining a uniform way of performing RPCs using HTTP as the underlying communications protocol with XML for the data serialization.
Drilling inside SoapHttpClientProtocol class
Advantages of Web services
SOA â€“ Service Oriented Architecture, Four Tenets

Thanks,

~ Ankit

Ajax Tutorial Series

Ankit — Fri, 20 Oct 2006 06:18:54 +0000

Want to learn Ajax from scratch? Here is a series of tutorials for you.

Mastering Ajax, Part 7: Using XML in requests and responses
Brett McLaughlin demonstrates how you can use XML as the data format for sending asynchronous requests.

Mastering Ajax, Part 6: Build DOM-based Web applications
Continue to explore how DOM programming fits into interactive Ajax applications as Brett McLaughlin completes his trilogy of articles on DOM programming with a DOM application in practice.

Mastering Ajax, Part 5: Manipulate the DOM
Last month Brett introduced the Document Object Model, whose elements work behind the scenes to define your Web pages. This month he dives even deeper into the DOM. Learn how to create, remove, and change the parts of a DOM tree, and take the next step toward updating your Web pages on the fly!

Mastering Ajax, Part 4: Exploiting DOM for Web response
The great divide between programmers (who work with back-end applications) and Web programmers (who spend their time writing HTML, CSS, and JavaScript) is long standing. However, the Document Object Model (DOM) bridges the chasm and makes working with both XML on the back end and HTML on the front end possible and an effective tool. In this article, Brett McLaughlin introduces the Document Object Model, explains its use in Web pages, and starts to explore its usage from JavaScript.

Mastering Ajax, Part 3: Advanced requests and responses in Ajax
For many Web developers, making simple requests and receiving simple responses is all they’ll ever need, but for developers who want to master Ajax, a complete understanding of HTTP status codes, ready states, and the XMLHttpRequest object is required. In this article, Brett McLaughlin will show you the different status codes and demonstrate how browsers handle each and he will showcase the lesser-used HTTP requests that you can make with Ajax.

Mastering Ajax, Part 2: Make asynchronous requests with JavaScript and Ajax
Most Web applications use a request/response model that gets an entire HTML page from the server. The result is a back-and-forth that usually involves clicking a button, waiting for the server, clicking another button, and then waiting some more. With Ajax and the XMLHttpRequest object, you can use a request/response model that never leaves users waiting for a server to respond. In this article, Brett McLaughlin shows you how to create XMLHttpRequest instances in a cross-browser way, construct and send requests, and respond to the server.

Mastering Ajax, Part 1: Introduction to Ajax
Ajax, which consists of HTML, JavaScript, DHTML, and DOM, is an outstanding approach that helps you transform clunky Web interfaces into interactive Ajax applications. The author, an Ajax expert, demonstrates how these technologies work together — from an overview to a detailed look — to make extremely efficient Web development an easy reality. He also unveils the central concepts of Ajax, including the XMLHttpRequest object.

~ Ankit

[Edited on March 20, 2007:

One more classsic tutorial for Ajax basics: http://www.harrymaugans.com/2007/03/18/tutorial-ajax-made-easy/

]

AJAX Guide !

Ankit — Mon, 31 Jul 2006 09:09:42 +0000

Johnson compiles a useful list of Ajax resources. It contains resource for PHP/Java/ASP.net.

[Edited: Oct 13th, 2006]
And here we go to hack an Ajax website.

Using ‘Firebug’ (and extension to FireFox) you can discover ajax calls, stack trace of errors, etc;
Using ‘chickenfoot’ provides a programming environment within the browser (ie. simulation of user clicks, etc;)

~ Ankit