Map Reduce Simplified

Yes it is about parallel and distributed computing, there are tonnes of web pages, books articles, diagrams etc. etc with nice buzz words to talk about Map Reduce, here is the most simplified explanation.

Lets take a real life example.

1. Company CEO called all Program Manager's "I need total effort spent this month by noon". Program Manager's no problem sir. Why are Program Manager's not worried because they are going to distribute task :-)

2. Each Program Manager called their project manager asking for effort spent so far.

3. Each Project Manager pulled up effort sheet and provided it to their Program Managers.

4. Program Managers complied received sheet into one file and sent it to CEO.

5. Company CEO collated all the sheets and calculated total effort spent.

Each individually broke its task to smaller tasks (Mapped its input task to smaller tasks), Program Manager was required to provide effort spent, he mapped his task to smaller tasks, this is MAP.

Program Manager's on receiving data from their project managers compiled it back to single output, this is REDUCE.

Now lets zoom out and summarize how Map Reduce applies to distributed and parallel computing. Each node distributes its task to smaller tasks(Maps its given task). Each node receive results, combine them(REDUCE) to generate required output.

Apache Roller Getting Started

If you are thinking to setup a blog website then apache roller is the quickest and simplest thing to do so, below are steps for getting started, though these instructions are present in documentation provided by apache, but hopefully following steps will make it very easy for you.

Here you Go !!

1. Download apache roller

http://roller.apache.org/download.cgi#roller50

2. Install Tomcat

http://tomcat.apache.org/download-70.cgi

3. Download mysql

http://dev.mysql.com/downloads/

4. Unzip apache roller zip file and copy roller-5.0.1-tomcat.war from
\roller-weblogger-5.0.1-for-tomcat.zip\roller-weblogger-5.0.1-tomcat\webapp to tomcat webapps folder

5. Create mysql database, dont worry about schema, that will be automatically created later.

mysql -u root -p

password: *****

mysql> create database rollerdb;

mysql> grant all on rollerdb.* to scott@'%' identified by 'tiger';
mysql> grant all on rollerdb.* to scott@localhost identified by 'tiger';

Otherwise you will get following error on webpage:

[com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: Unknown database 'rollerdb'

6. Create a file roller-custom.properties in tomcat lib folder, here is default content:

installation.type=auto
mediafiles.storage.dir=/usr/local/rollerdata/mediafiles
search.index.dir=/usr/local/rollerdata/searchindex
log4j.appender.roller.File=/usr/local/rollerdata/roller.log
database.configurationType=jdbc
database.jdbc.driverClass=com.mysql.jdbc.Driver
database.jdbc.connectionURL=jdbc:mysql://localhost:3306/rollerdb?
autoReconnect=true&useUnicode=true&characterEncoding=utf-8&mysqlEncoding=utf8
database.jdbc.username=scott
database.jdbc.password=tiger
mail.configurationType=properties
mail.hostname=smtp-server.example.com
mail.username=scott
mail.password=tiger

If you dont add this file then you will get following error on startup:

Roller Weblogger: No customer properties found in classpath

7. Please download and copy jars for mail api and mysql jdbc drivers to lib directory of tomcat

mail.jar
mysql-connector-java-5.1.22-bin.jar

I came across following error and copying mail.jar to lib directory fixed it.

SEVERE: Error listenerStart
Jan 28, 2013 11:03:29 AM org.apache.catalina.core.StandardContext startInternal
SEVERE: Context [/roller-5.0.1-tomcat] startup failed due to previous errors
Jan 28, 2013 11:03:29 AM org.apache.catalina.loader.WebappClassLoader clearRefer
encesThreads
SEVERE: The web application [/roller-5.0.1-tomcat] appears to have started a thr
ead named [Abandoned connection cleanup thread] but has failed to stop it. This
is very likely to create a memory leak.

8. Start tomcat and open following url

http://localhost:8080/roller-5.0.1-tomcat/

9. If you have followed all the steps, you should see following screen:



10. Click on "Yes - create tables now", once the tables are created you will see following confirmation message.

Database tables were created successfully as you can see below.
Database tables are present and up-to-date. Click here to complete the installation process and start using Roller.

Click on "Here"

11. You should now see welcome message

"Welcome to Roller"

12. Follow on screen steps to create a user and blog.

Hopefully you will find it very simple to setup and have fun setting up your blog site in few minutes.

HTML5 Cool Features

HTML5 has come up with lot of features but coolest of them are MathML and SVG support. Tried few quick examples, they make web designing more fun:




If you don't see a green circle, red rectangle and a blue line then your browser does not support HTML5, visit following URL to check your browser:

http://html5test.com/

Good luck for rich GUI's.

View Drools Generated Code

When we execute rules, behind the scene java code is generated which is actually getting executed, to see this java code you need to set configuration path where you want java code generated by drools to be stored.

PackageBuilderConfiguration configuration = new PackageBuilderConfiguration();
configuration.setDumpDir(new File("XYZ"));

final KnowledgeBuilder kbuilder = KnowledgeBuilderFactory
.newKnowledgeBuilder(configuration);

Set XYZ as a directory path where you would like drools to store generated code. e.g. XYZ = "c:/drools/codegen"

When you run your program the java classes generated for the .drl files are stored at the path XYZ.

This generated code is really helpful to understand the behavior in lot of situations.

JSON Optimizing for Faster Rendering

All web applications have fast rendering as one of the primary goals, JSON is a preferred choice in most of AJAX based applications because it is lightweight data interchange format.

Consider a scenario where you have to read data from database and render it on UI, typically the steps which will be followed are:

a. Send request data to server using AJAX calls
b. At server end invoke the Business layer
c. Business layer calls the database layer
d. Data returned from database layer is populated into business objects
e. From business objects build JSON objects, send them back to client
f. Client use Javascript libraries to render data on UI.

If everything works fine for you, you can stop reading right now, because you are achieving the required goal in the best way.

But in real world this might not be working for you because of performance issues at one or the other step mentioned above. Here are few performance tips, they might suite in some of the scenarios and might be the worst suggestion in other cases:

1. Store JSON objects in database, read them send them to UI. It will be the fastest Way but how to query, we need to build JSON object from our business objects before sending them to UI.

2. Store JSON objects in one of the columns in database, query on other columns and return the column containing the JSON Object.

These tips might be useful in some of the scenario's, also use JSON API's to add methods to generate JSON objects out of Java Objects.

Hope they might help you, might not help some of you.

Good Luck for faster UI's

Drools - An overview

For Java based applications the most challenging part has always been the business logic maintenance, and pick any applications which you find complex and if we ask ourself how complex it would be moving forward, the answer will always be nX times.

What do we do ? Drools comes for Rescue as a Rule Engine.

Drools provides mechanism:

a. To write business logic in simple english language
b. Easy to maintain and very simple to extend
c. Reusability of logic by defining keywords in a DSL file and using them in DSLR file.

But be careful nothing comes free, everything takes cost in terms of memory and time space.

Use Drools if you really have :

a. Business logic which you think is getting cluttered with multiple if conditions because of variety of scenarios
b. You will have growing demand of increase in the complexity
c. The business logic changes would be frequent (1 - 2 times a year would also be frequent)
d. Your server's have enough of memory as it is a memory hungary tool, it provides performance at cost of memory

Choosing a technology stack is a big decision for the lifecycle of an application, so evaluate both pros and cons and if they fits in your application requirements go for it because it is one of the easiest to use and plug in Java based Rule Engine.

Some programmers might find it cumbersome as we are used to looking at the code which is being executed and loves to debug it and understand it and see what is actually happening, latest version of Drools 5.0 address this by providing JMX support and functionality to see the generated Java Code.

Good Luck with your Rule Engine !!

Class Data Sharing

Class data sharing (CDS) a feature introduced in J2SE 5.0 reduces the startup time for Java
programming language applications.

When the JRE is installed on 32-bit platforms using the Sun provided installer, the installer loads a set of
classes from the system jar file into a private internal representation, and dumps that representation to a file,
called a "shared archive".Class data sharing is not supported in Microsoft Windows 95/98/ME.

During subsequent JVM invocations, the shared archive is memory-mapped in, saving the cost of loading those
classes and allowing much of the JVM's metadata for these classes to be shared among multiple JVM processes.

The primary motivation for including CDS in the 5.0 release is the decrease in startup time it provides.
CDS produces better results for smaller applications because it eliminates a fixed cost: that of loading
certain core classes. The smaller the application relative to the number of core classes it uses, the
larger the saved fraction of startup time.


The footprint cost of new JVM instances has been reduced in two ways. First, a portion of the shared archive,
currently between five and six megabytes, is mapped read-only and therefore shared among multiple JVM processes.
Previously this data was replicated in each JVM instance. Second, since the shared archive contains class data
in the form in which the Java Hotspot VM uses it, the memory which would otherwise be required to access the
original class information in rt.jar is not needed. These savings allow more applications to be run concurrently
on the same machine.

Regenerating Shared Archive

To regenerate the share archive use the following command:

java -Xshare:dump

Diagnostic information will be printed as the archive is generated.

Manually Controlling Class Data Sharing

The class data sharing feature is automatically enabled when conditions allow it to be used. The following command
line options are present primarily for diagnostic and debugging purposes and may change or be removed in future
releases.

-Xshare:off
Disable class data sharing.

-Xshare:on
Require class data sharing to be enabled. If it could not be enabled for various reasons, print an error message and exit.

-Xshare:auto
The default; enable class data sharing whenever possible.

XML Naming Conventions (Best Practices)

XML is the base of Web 2.0 development. While writing a web service to integrate products, I learned some best practices with XML naming conventions.

An XML element is everything from (including) the element's start tag to (including) the element's end tag.

An element can contain other elements, simple text or a mixture of both. Elements can also have attributes.

<bookstore>
<book category="CHILDREN">
<author>J K. Rowling</author>
<year>2005</year>
<price>29.99</price>
</book>
<book category="WEB">
<author>Erik T. Ray</author>>
<year>2003</year>
<price>39.95</price>
</book>
</bookstore>>

In the example above, and have element contents, because they contain other elements. has text content because it contains text.

In the example above only has an attribute (category="CHILDREN").

XML Naming Rules

XML elements must follow these naming rules:

1. Names can contain letters, numbers, and other characters
2. Names cannot start with a number or punctuation character
3. Names cannot start with the letters xml (or XML, or Xml, etc)
4. Names cannot contain spaces

Any name can be used, no words are reserved.

Best Naming Practices

1. Make names descriptive. Names with an underscore separator are nice: , .
2. Names should be short and simple, like this: not like this: .
3. Avoid "-" characters. If you name something "first-name," some software may think you want to subtract name from first.
4. Avoid "." characters. If you name something "first.name," some software may think that "name" is a property of the object "first."
5. Avoid ":" characters. Colons are reserved to be used for something called namespaces (more later).
6. XML documents often have a corresponding database. A good practice is to use the naming rules of your database for the elements in the XML documents.
7. Non-English letters like éòá are perfectly legal in XML, but watch out for problems if your software vendor doesn't support them.

Reference : http://www.w3schools.com/xml/xml_elements.asp

Apache AXIS2 Web Service Client

This article covers details about writing a web service client using Apache AXIS2 API. The article explains the various API using code snippets and covers parameters require by various methods of web service client API.

Apache AXIS2 web service API mainly consists of two type of objects ServiceClient and OperationClient. ServiceClient provides basic APIs to send and receive SOAP messages, for advanced methods you require Operation Client.

To provide target URL you need to define a EndPointReference type of object.

EndpointReference targetEPR = new EndpointReference(http://localhost:8080/axis2/services/helloworld);

Various options can be given to web service client by creating an Options object. The reference point defined is set into the options along with the Transport protocol.

Options options = new

Options();

options.setTo(targetEPR);

options.setTransportInProtocol(Constants.TRANSPORT_HTTP);

Now create a service client and pass these options to service client using setOptions API of service client.

ServiceClient sender = new ServiceClient();

sender.setOptions(options);

So, till now we have created a service client and provided the various options to it, next step is creating the payload of SOAP message that will be send in the web service call. AXIS2 provides AXIOM (AXIS Object model) to create XML Structure. Following code snippet creates the payload message.

OMFactory fac = OMAbstractFactory.getOMFactory();

OMNamespace omNs = fac.createOMNamespace("http://ws.apache.org/axis2", "");

OMElement method = fac.createOMElement("sayHello", omNs); //Method to be invoked.

OMElement value = fac.createOMElement("parameter1", omNs);

value.addChild(fac.createOMText(value, "Sachin" ));

method.addChild(value);

value = fac.createOMElement("parameter2", omNs);

value.addChild(fac.createOMText(value, "Thapa" ));

method.addChild(value);

Finally use the sendReceive API of ServiceClient to send SOAP request and receive response.

OMElement result = sender.sendReceive(method);

System.out.println(result);

The result object contains the response received from the server.

Project Properties Holder - Singleton Design Pattern Example

A very common requirement in most of the project is managing project specific properties. Certain properties that are required at various points of flow in a project. Mostly people would like to have a solution in which to change these properties they dont have to dig out the code and change the values. Instead they would like to have some file external to the code, so that anybody with or without knowledge of code can change it. A few examples for such properties can be:

a) A project connects to a 3rd party, one may like to store the URL for the connection in a properties file.

b) A project generates a output file, one may like to store the prefix or naming convention pattern in the properties file.

There can be many more examples. Now we need to look out for a solution so that we have single point to fetch these properties. The answer comes from Singleton design pattern.

Create a singleton class PropertiesHolder.java as shown below:

import java.io.IOException;
import java.util.Properties;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

public class PropertiesHolder
{
private final Log log = LogFactory.getLog(PropertiesHolder.class);
private Properties properties = null;
private static PropertiesHolder holder = null;


public static PropertiesHolder getInstance()
{
if(holder == null)
{
holder = new PropertiesHolder();
holder.init();
}
return holder;
}
private PropertiesHolder()
{

}
private synchronized void init()
{
if(properties == null)
{
try
{
properties = new Properties();
properties.load(PropertiesHolder.class.getResourceAsStream("/project.properties"));
}
catch (IOException e)
{
log.error("Error loading runtime properties file.", e);
}
}
}

public String getProperty(String propertyName)
{
return properties.getProperty(propertyName).trim();
}
}

Project properties will be loaded once when first call is made to get a property. Any properties that are required to be changed are to be changed in project.properties file.

You may like to have a method to set property as well, the set property method will be required to update the Properties object and write that to file as well. In case the number of properties are too many and required to managed by an Admin, you can provide a UI over it as well.

Deploying Web Service in Apache AXIS2

The purpose of this article is to talk about how to write web service and deploy it in Apache AXIS2.

First step is downloading and installing apache axis2. There are two ways to use Apache AXIS2.

1. Install AXIS2 as a standalone server using the Standard Binary Distribution.
2. Deploy axis2.war and deploy it in a servlet container.

We will be using the 2nd method in the article. To check the installation open the url http://localhost:8080/axis2 and you should be able to see the home page of apache axis2.

Please locate the folder axis2\WEB-INF\services in exploded war file of axis2. This is the folder where you will copy the code of your service and it will get deployed in apache axis2.

Lets us take a simple example. Write your service class.

public class HelloWorld
{
public String sayHello(String firstName, String lastName)
{
System.out.println("Hello World Invoked");
MessageContext incomingContext = MessageContext.getCurrentMessageContext();
FileDataSource dataSource = new FileDataSource("c:/YServer.txt");
DataHandler dataHandler = new DataHandler(dataSource);
incomingContext.addAttachment("contentID", dataHandler);

String data = DataProvider.getData();
return "Hello " + firstName + " " + lastName + " " + data;
}
public String getServiceName()
{
return "test service";
}
}

Write a services.xml file.

<service>
<description>
This is my first service, which says hello
</description>
<parameter name="ServiceClass">HelloWorld</parameter>
<operation name="sayHello">
<messageReceiver class="org.apache.axis2.rpc.receivers.RPCMessageReceiver"/>
</operation>
<operation name="getServiceName">
<messageReceiver class="org.apache.axis2.rpc.receivers.RPCMessageReceiver"/>
</operation>
</service>

In case you want to receive the SOAP payload as XML Message in the service you need to specify XML Message receiver instead of RPCMessageReceiver in services.xml file. To specify XML Message receiver put the following line as child of <operation> tag in your services.xml.

<messageReceiver

class="org.apache.axis2.receivers.RawXMLINOutMessageReceiver"/>

Also, since the service will receive XML Message as input parameter you need to change the signature of the method of service.

public OMElement sayHello(OMElement element)

OMElement object contains the XML Message, OMElement Object is provided by AXIOM. AXIOM stands for AXis Object Model (also known as OM - Object Model) and refers to the XML infoset model that was initially developed for Apache Axis2.


Bundle your class file, services.xml in the hierarchy as shown in the figure below. See helloworld folder in image below.



Copy your service into the services folder of axis2 as shown in figure, start web server. Open the URL http://localhost:8080/axis2.

On the displayed page Click on services, you should be able to see the name of service you specified in services.xml in the list of web services.

Getting Started with Apache Lucene

Apache Lucene is a high-performance, full-featured text search engine library.

The API of lucene is very simple to use. Here is overview of some of the objects required to start using Apache Lucene.

Document and Fields

The class "org.apache.lucene.document.Document" is necessary container for the index. Lucene requires all indexed objects to provide an instance of Document. Each document defines one or several fields ( (org.apache.lucene.document.Field). Fields contain classified information about the document or metadata related to document. A sample classification is for example the creation date of a file, author of the document etc. These fields allow you to search later for a specific information in this classification.


IndexWriter

The class org.apache.lucene.index.IndexWriter creates the index. Via the method addDocument you can add an existing Document to the index. The constructor for IndexWriter expects the directory to store the index, and the analyzer for the content of the files. In addition a boolean flag is handed over which indicates if the index should be created new or if an existing index should be extended.

Analyser

The class org.apache.lucene.analysis.standard.StandardAnalyzer provides a standard analyzer. This part is responsible to analyse the text and to filter out certain fill-words, e.g. "and".

Searcher and Query

The class org.apache.lucene.search.Searcher provides the search functionality. org.apache.lucene.search.IndexSearcher searches over an index. What is to be searched is provided via the query (org.apache.lucene.search.Query) class. The search allows wildcard search, e.g. *, ?, logical operations (AND, OR, NOT) and much more, e.g. fussy.

Here's a simple example how to use Lucene for indexing and searching.

public class TestMyLucene
{
public static void main(String[] args) throws Exception
{
Analyzer analyzer = new StandardAnalyzer();

// Store the index in memory:
Directory directory = new RAMDirectory();

// To store an index on disk, use this instead (note that the
// parameter true will overwrite the index in that directory
// if one exists):
//Directory directory = FSDirectory.getDirectory("/tmp/testindex", true);
IndexWriter iwriter = new IndexWriter(directory, analyzer, true);
iwriter.setMaxFieldLength(25000);

Document doc = new Document();
String text = "This is the text to be indexed.";
doc.add(new Field("fieldname", text, Field.Store.YES, Field.Index.TOKENIZED));
iwriter.addDocument(doc);
iwriter.close();

// Now search the index:
IndexSearcher isearcher = new IndexSearcher(directory);

// Parse a simple query that searches for "text":
Query query = QueryParser.parse("text", "fieldname", analyzer);
Hits hits = isearcher.search(query);
System.out.println(hits.length());

// Iterate through the results:
for (int i = 0; i < hits.length(); i++)
{
Document hitDoc = hits.doc(i);
System.out.println(hitDoc.get("fieldname"));
}

isearcher.close();
directory.close();
}
}

In the above example, hits return the matching documents for the query provided.

Calling Struts Action by Javascript

To call a struts action by Javascript on an event, you need to write a function which is invoked when the event occurs and this function makes an AJAX call. The AJAX call can send a request to the same URL which is provided in action attribute of form tag or html:form tag.

e.g. In case your action URL is something like
"/registerUserAction.do?action=forgetPasswordForward"
that you provide in action attribute of html:form, you can pass the same url to the mentioned code snippet below:


function makeRequest(url, callbackfunction)
{
var http_request = getXMLHttpObject();
url = url + "isComingFromAjax=true";

if (url.indexOf('?') != -1)
{
url = url + "&" ;
}
else
{
url = url + "?" ;
}

url = url + "isComingFromAjax=true";
http_request.onreadystatechange = callbackfunction;
http_request.open('POST', url.substring(0, url.indexOf('?')), true);
http_request.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
http_request.send(url.substring(url.indexOf('?') + 1));
}

Some of points to be considered in given code snippet:
1. callbackfunction is the function which will be invoked when response is received
2. "isComingFromAjax=true" parameter has been added as a extra parameter to differentiate between the normal action request and the AJAX request to do any special handling on the server side.

I have not covered details of creating XMLHttpRequest Object and other AJAX related things assuming you know it. You can write the logic for handling the response received from server in callbackfunction.

Oracle - Rank Function

Rank calculates the rank of a value in a group of values. Rows with equal values for the ranking criteria receive the same rank. Oracle then adds the number of tied rows to the tied rank to calculate the next rank. Therefore, the ranks may not be consecutive numbers.

Consider the following Schema

CREATE TABLE USER_TEST
(
user_id numeric(12),
first_name varchar2(32),
last_name varchar2(32),
age numeric(3),
salary numeric(7)
);

insert into user_test values(1, 'Pardeep', 'Kumar', 26, 20000);
insert into user_test values(2, 'Raj', 'Sharma', 23, 15000);
insert into user_test values(3, 'Jai', 'Singh', 30, 30000);
insert into user_test values(4, 'Rana', 'Pratap', 32, 35000);
insert into user_test values(5, 'Nakul', 'Gupta', 23, 16000);
insert into user_test values(6, 'Ritu', 'Kumar', 22, 10000);
insert into user_test values(7, 'Sita', 'Dikshit', 27, 22000);
insert into user_test values(8, 'Gurpal', 'Bhatia', 38, 49000);
insert into user_test values(9, 'Bhim', 'Kumar', 23, 19000);
insert into user_test values(10, 'Lokesh', 'Shriram', 22, 11500);

Aggregation

As an aggregate function, RANK calculates the rank of a hypothetical row identified by the arguments of the function with respect to a given sort specification.

The constant argument expressions and the expressions provided in the ORDER BY clause of the aggregate match by position. Therefore, the number of arguments must be the same and their types must be compatible.

Single Column RANK as Aggregation Function

Syntax:

RANK () WITHIN GROUP (ORDER BY NULLS )

Example:
The following query returns the rank for a user with salary 10,000SELECT RANK(20000) WITHIN GROUP
(ORDER BY salary DESC NULLS LAST) SAL_RANK
FROM user_test;

Result: SAL_RANK = 5

Multiple Column RANK as Aggregation Function

RANK () WITHIN GROUP (ORDER BY NULLS )

The following query returns the rank of a user a salary of 15,000 and age 23 years.

SELECT RANK(23, 15000) WITHIN GROUP
(ORDER BY age desc, salary desc) RANK
FROM user_test;

Result: Rank = 8


Analytic

As an analytic function, RANK computes the rank of each row returned from a query with respect to the other rows returned by the query, based on the values of the value_exprs in the order_by_clause.

RANK Analytic Function

RANK () OVER ()

Find the user with the 2nd highest salarySELECT * FROM (SELECT user_id, first_name, last_name, salary, RANK() OVER (ORDER BY salary DESC) userrank
FROM user_test) WHERE userrank = 2;

Result:

USER_ID FIRST_NAME LAST_NAME SALARY USERRANK
4 Rana Pratap 35000 2 RANK() OVER ( )

Arrange table by age and then salary

SELECT user_id,first_name, last_name, age, salary,
RANK() OVER (PARTITION BY age ORDER BY salary DESC) RANK
FROM user_test;

Result:

USER_ID FIRST_NAME LAST_NAME AGE SALARY RANK
10 Lokesh Shriram 22 11500 1
6 Ritu Kumar 22 10000 2
9 Bhim Kumar 23 19000 1
5 Nakul Gupta 23 16000 2
2 Raj Sharma 23 15000 3
1 Pardeep Kumar 26 20000 1
7 Sita Dikshit 27 22000 1
3 Jai Singh 30 30000 1
4 Rana Pratap 32 35000 1
8 Gurpal Bhatia 38 49000 1


Return all users with age 23 ordered by salary

SELECT user_id,first_name, last_name, age, salary,
RANK() OVER (PARTITION BY age ORDER BY salary DESC) RANK
FROM user_test where age = 23;

USER_ID FIRST_NAME LAST_NAME AGE SALARY RANK
9 Bhim Kumar 23 19000 1
5 Nakul Gupta 23 16000 2
2 Raj Sharma 23 15000 3

Although the examples quoted here may looks like that we are paying more cost for the same things that can be done by simple order by, but simple examples have been chosen to make it easy to understand how to use RANK.

Generating Image Thumbnails

When I started working on this initially, I started looking into open source tools for this, after spending couple of hours on open source tools I suddenly jumped into oracle site and was pleased to see a good support for image processing in oracle. Oracle provides support to create thumbnail of images stored as blob. Here is simplest way to create image thumbnails. Create a table that will store the original image and the thumbnail image content as blob.

CREATE TABLE test_thumbnail
(
id NUMERIC(12) PRIMARY KEY,
image_content BLOB,
thumbnail_content BLOB
);

Create a stored procedure that will update the thumbnail_content field after image is stored in the database.

create or replace PROCEDURE IMAGE_THUMB_PROCEDURE
(imgId IN NUMBER , imgAttribute IN varchar2) AS
imageId integer := 0; verb varchar2(100);
src_blob BLOB;
dst_blob BLOB;
BEGIN imageId := imgId; verb := imgAttribute;
update test_thumbnail set thumbnail_content=empty_blob() where id = imageId;
select image_content into src_blob from test_thumbnail where id = imageId;
select thumbnail_content into dst_blob from test_thumbnail where id = imageId for update; ordsys.ordimage.processCopy(src_blob ,verb ,dst_blob);
update test_thumbnail set thumbnail_content = dst_blob where id = imageId;
END IMAGE_THUMB_PROCEDURE;

Invoke the stored procedure passing the appropriate imgAttribute, passing different kind of image attributes you can process the original image content, for scaling down the image to a thumbnail of 100x100 pixels, pass the following parameter:

“maxscale=100 100 fileformat=jfif”

Maxscale is the size of the generated image and fileformat has its obvious meaning. The method ordsys.ordimage.processCopy(src_blob ,verb ,dst_blob) copy a source blob into a destination blob doing the processing as per attributes passed as verb.

For more details on oracle media solution support please read the following article: http://www.oracle.com/technology/sample_code/products/intermedia/index.html

Once the stored procedure is invoked image thumbnail is stored as blob in field thumbnail_content.

Difference between Delete, Drop and Truncate Statements

DELETE, DROP and TRUNCATE statements differ in their nature itself.
a. DELETE statement is a DML (DATA MANIPULATION LANGUAGE) statement.
b. DROP AND TRUNCATE statements are DDL (DATA definition language) statements.

A DML action can be rolled back if the data is not committed, but DDL actions cannot be rolled back until Oracle 9i. With Oracle 9i FLASH BACK enabled even some of the DDL statements can be rolled back.

Delete

A delete statement deletes the data from a table. A delete statement can have a “where” clause, which need to be satisfied for the data to be deleted from the table.

Actions of Delete statement

• Deletes the data from the current table space.
• Modifies the undo table space with the delete records.
• Executes all the before / after statement and row level triggers.
• Updates the indexes (makes the index empty if the where clause is omitted).
• Constraint checks are performed before deleting the rows
  

Syntax of a delete Statement:
DELETE FROM table [WHERE condition]

Truncate

Truncate drops all the records in a table. But as it is a DDL statement data cannot be retrieved. Usually truncate is faster than delete statement because there is no need to change or update the UNDO table space with the deleted records. Truncate is an implicit commit Statement. Truncate statement deal locates the space.

Actions of Truncate Statement
a. Removes all the records from the current table space.
b. Updates the indexes.
c. High watermark of the truncated table is reset.
d. Integrity Constraint checks are performed

Syntax of a Truncate Statement:
TRUNCATE TABLE table_name;

DROP STATEMENT

A drop statement removes the table object from the database. Structure and the data will be removed from the database. Action cannot be rolled back (but only by FLASH BACK from Oracle 9i).

Actions of a Drop Statement:
a. Constraint checks are performed before dropping.
b. All the data and structure of the table will be removed.
c. Updates the corresponding data dictionary views like dba_objects, dba_tables, user_tables e.t.c
d. Updates the Status as “INVALID” for all the dependent objects.
e. Deallocates the Space

Syntax of a Drop Statement:
DROP TABLE table_name;
DROP TABLE table_name cascade constraints;

If “cascade constraints” is specified all foreign keys that reference the table are dropped and then table is dropped.