• Stream URL: mms://cctv-live-cctv1.wm.llnwd.net/cctv_live_cctv9

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DB2 uses a dictionary based algorithm for compressing data records. DB2 9 will scan tables, and search for duplicate occurrences, then assign a short numeric key to each entries. You will understand better with a picture:

Compress data

Each new occurences of “Sophie”, “New York”, “IBM US”, will be respectively assign to “(01)”, “(19)” and “(09)”. This is very useful on large table. Each time a new row is added to the table, DB2 will automatically compress these new data.

Seems to be good, let’s try on our DB2 now. To enable the compression, we should turn on the “COMPRESS” option on the table.

CREATE TABLE Users COMPRESS YES

or use alter if the table is already created:

ALTER TABLE Users COMPRESS YES

Typically, we can save an average ratio of 45 to 75 percent of our storage space. Next time, we’ll see how to use the inspect tool, to determine the compression ratio.

To define this variable, let’s use the DB2set command:

Db2set DB2_CLPPROMPT="db2isgreat> "

Our new DB2 Prompt will be “db2isgreat> “. It’s much more better, but we can do more. DB2_CLPPROMPT registry variable can contain the tokens %n, %ia, %d, %da and %i:

• %n – New line
• %ia – Authorization ID of the current instance attachment
• %d – Local alias of the currently connected database
• %da – Authorization ID of the current database connection
• %i – Local alias of the currently attached instance

Now, let’s try with these tokens:

Db2set DB2_CLPPROMPT="%ia@%i, %da@%d> "

With an instance attachment to instance “DB2″ with authorization ID “mycado”. Database “sample” with authorization ID “mycadoax”, will return something like:

MYCADO@DB2, MYCADOAX@SAMPLE >

You can now everytime where you are, and one which instance/database you’re working on.

It’s easy, you have three basic statements:

• JOB: Provides a name (jobname) for the batch.
• EXEC: Provides the name of a program to execute.
• DD: For Data Definition, provides inputs/outputs to the program.

Let’s see a JCL example:

//MYJOB     JOBTES 1
//MYSORT    EXEC PGM=SORT
//SORTIN    DD DISP=SHR,DSN=SUP01.TAB.TEST
//SORTOUT   DD SYSOUT=*
//SYSOUT    DD SYSOUT=*
//SYSIN     DD *
SORT FIELDS=(1,4,CH,A)
/*

Now, try to understand what’s happen here.

• MYJOB is the jobname associates to the workload, here it’s “JOBTES”.
• MYSORT is the stepname, which ask the system to execute a program called “SORT”.
• SORTIN is the program input, here with the DSN (Data Set Name) SUP01.TAB.TEST, and the dataset can be shared (DISP=SHR).
• SORTOUT is the SORT program output.
• SYSOUT specifies to send system output to JES (Job Entrey Subsystem), but it’s also possible to send the outpu to a dataset.
• SYSIN tell the SORT program which fields of the SORTIN data records are to be sorted.

Enough for the moment, JCL is quite hard at beginning !

For the SQL query, nothing more than a SELECT:

SELECT id, info from client

Easy, but not really powerful for XML data, let’s try with XQuery, who give us two functions for DB2. db2-fn:sqlquery and db2-fn:xmlcolumn. The first function retrieves a sequence that is the result of an SQL fullselect and the second retrieves a sequence from a column. One important thing you should keep in mind, SQL is not a case-sensitive language alors que XQuery is a case-sensitive language.

An example which return all the XML data from the “info” column:

XQUERY db2-fnxmlcolumn ('CLIENT.INFO')

Which is same as this SQL query:

SELECT info FROM client

Let’s see something more nice. This query will return all the elements in <name> , inside the “info” column, and with the <city> element which containt “Paris”:

XQUERY declare defaut element namespace "http://posample.org";
for $d in db2-fn:xmlcolumn('CLIENT.INFO')/clientinfo
  where $d/addr/city="Paris"
return <out>{$d/name}</out>

db2-fn:xmlcolumn retrieves the data from the “info” column in the “client” table. We add a $d variable, for each element of <clientinfo>, and we use a where to filter the <city> element which should be “Paris. To finish, we use <out> to output the data:

<out xmlns="http://posample.org">
  <name>Sophie Bool</name>
</out>

XQUERY declare default element namespace "http://posample.org";
for $d in db2-fn:sqlquery('SELECT info FROM client')/clientinfo
  where $d/addr/city="Paris
return <out>{$d/name}</out>

So, it’s funny, but why it’s interesting to do that ? Because XML data are hierarchic (instead of relational data which are flat) and data self-describing through XML tags. XML also allows a better flexibility for data structures required to change very often. In the other hand, access time performances will be a little slower, we lose the integrity constraints, and OLAP queries will be more difficult. The important question is “Which flexibility-performance ratio do you need ?”.

Let’s start now with the creation of a database, which should be encoded with UTF-8, to store XML. For that, we use the CREATE DATABASE command:

CREATE DATABASE xmldb USING CODESET UTF-8 TERRITORY US

We have our table, now we should create the “client” table, with an “info” column who contain client information, in XML format:

CONNECT TO xmldb
CREATE TABLE client (id INT, info XML)

Let’s try to insert a new client with a SQL query:

INSERT INTO client (id, info) VALUES (1, '<clientinfo xmlns="http://posample.org" Cid="1"><name>Sophie Bool</name><addr country="France"><street>5 rue du chateau de stable</street><city>Paris</city></addr><phone type="work">01 72 92 02 88</phone></clientinfo>')

The first thing you will told me is this query is a normal SQL query, and this is right, insert XML isn’t more difficult. The second thing is about the XML, here we have a short XML data, but if we have more, it will be very difficult to use. This why, we will use XQuery to manipulate these data or use a XDS import. I’ll come back soon on these points.

First we need to create a Jabber Account on Adium, we will use a special “ID”, which is your ID on Renren. If you don’t know your ID, just go to you profile page (个人主页), and look at the address bar, for me it’s like:

Profile address bar

Just not the number after the “id=“. My Jabber ID (用戶名) will be “250388793@renren.com” and the password (密碼) will be the same as my Renren password.

Now let go to the Options pane (帳戶選項), to modify the connect server (服務器) option to “talk.renren.com” and verify that the port (端口) is “5222“. Then .. it’s finish, confirm and connect ! You’ll see all your friends, organized by groups :)

This new release come with a new default theme called Twenty Ten, which is coming with new APIs allowing easy modification of the background, headers, shortlinks, menus, post types,.. MU and WordPress as been merged to make it possible to run one blog or ten million from the same installation. And also a new lighter interface, contextual help, more than 1,200 bug fixes and feature enhancements. For more information just go to the Codex WP 3.0 or just watch the video:

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