Sun buys MySQL....

Well, the news is pretty old now. Everyone has had his say on the deal: How its a great deal for both the parties involved, for the competitors, and even MySQL's competitors (read my employer, EnterpriseDB (though we cater to a different market share)).

But I came across this interesting take on the deal. How Oracle might have orchestrated this deal. The claims are unsubstantiated, a good read nonetheless:

http://www.marketwatch.com/news/story/john-dvoraks-second-opinion-sun-mysql/story.aspx?guid=%7B88606B4A-A4AF-46FC-9C80-6B186A622456%7D&dist=hplatest

They can now track what you are thinking

It has been a research subject for many years at many places... controlling objects/actions with just your thought.

This recent one demonstrates how they have managed to track a monkey's brain activity, while he was walking, to make a robot walk in the same manner (across the globe; as if that mattered!)

Interesting read.

http://www.informationweek.com/shared/printableArticle.jhtml?articleID=205801020

IMified test blog

Just testing IMified to create blogs... Lets see how this turns up... Her we go..

Update: It wasn't all that fun... and it didn't feel very intuitive. You'd want to come back to your blog to review your post anyway! good tool though, if you need it, that is.

Mount USB drives in Write Protect (read only) mode

Under the the following key:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control

Create a new key called StorageDevicePolicies. In that key create a new DWORD value called WriteProtect and set it to 1.

This is known to work under Windows XP SP2, though you can try it on your other varioations of Windows.

Show difference between two Microsoft Word documents

So, you want to compare two versions of a doc (probably one circulated by you, and the other you received revised by somebody). Here's how to get it done:

1) Open the original document.
2) Go to menu 'Tools' > 'Compare and Merge Documents'
3) In the 'Open' dialog, point to the newer version of the document, and click open.
4) And you are done.

MS Word will show you the changes (like something new inserted, deleted, etc) with appropriate coloring.

Force Oracle to use an index for IS [NOT] NULL predicates.

In my previous post, I mentioned how Oracle can't keep track of NULLS in an index, and consequently, cannot use an index to satisfy the IS NULL predicates (WHERE clauses).

There is a way of making Oracle do that though....

If you are trying to make Oracle use an index-on-nullable-column, here's a nifty trick from a reader-comment at http://www.dba-oracle.com/oracle_tips_null_idx.htm :

SQL> select count(1) from t where n is null;

COUNT(1)
----------
334

Execution Plan
---------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=3 Card=1 Bytes=3)
1 0 SORT (AGGREGATE)
2 1 TABLE ACCESS (FULL) OF 'T' (Cost=3 Card=334 Bytes=1002)

SQL> create index tind on t(n, 1); ----> here 1 is just any arbitary value.

Index created.

SQL> exec dbms_stats.gather_table_stats(user,'t',cascade=>true);

PL/SQL procedure successfully completed.

SQL> select count(1) from t where n is null;

COUNT(1)
----------
334

Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=2 Card=1 Bytes=4)
1 0 SORT (AGGREGATE)
2 1 INDEX (RANGE SCAN) OF 'TIND' (NON-UNIQUE) (Cost=2 Card=3
34 Bytes=1336)


Sandeep Redkar

Postgres can... Oracle can't (index NULLs)

Well, it was a revelation.... For almost ages, I have been made to believe that NULLs cannot be indexed; primarily because Oracle chose not to, and I had used Oracle quite a lot in the past (and worked for them too at one time).

A couple of days ago I was asked by a developer (Arie) this very question, but in context of Postgres:

Subject: Are nulls indexed?
Body:
If I have an index on column A (null-able) will null values be indexed? Basically, if not, does it mean that such a query "select * from T where A is null" will have to do a full table scan?

I blindly said no... that was until I had to test something out based on his next question. And I was in fact surprised! Postgres can use a non-unique index for 'IS NULL' and 'IS NOT NULL' predicates!

Here's a small session to demonstrate that Postgres stores index-records for NULLs and can use such indexes for IS [NOT] NULL predicates:

postgres=# create table t ( a int, b char(32) );
CREATE TABLE
postgres=# create index t_i on t( a );
CREATE INDEX
postgres=# insert into t select s, s+1 from generate_series( 1, 1000000 ) as s;
analyze t;
INSERT 0 1000000
postgres=# analyze t;
ANALYZE
postgres=# select relpages, relname from pg_class where relname like 't%';
relpages | relname
----------+--------------------------
<snip>
8334 | t
2745 | t_i
(7 rows)

postgres=# explain select * from t where a is null;
QUERY PLAN
--------------------------------------------------------------
Index Scan using t_i on t (cost=0.00..8.38 rows=1 width=37)
Index Cond: (a IS NULL)
(2 rows)

postgres=# truncate t;
TRUNCATE TABLE
postgres=# insert into t select case s%5 when 0 then null else s end, s+1 from generate_series( 1, 1000000 ) as s;
INSERT 0 1000000
postgres=# reindex index t_i;
REINDEX
postgres=# analyze t;
ANALYZE
postgres=# select relpages, relname from pg_class where relname like 't%'; relpages | relname
----------+--------------------------
<snip>
8334 | t
2745 | t_i
(7 rows)

postgres=# explain select * from t where a is null;
QUERY PLAN
----------------------------------------------------------------------
Index Scan using t_i on t (cost=0.00..7332.37 rows=198972 width=37)
Index Cond: (a IS NULL)
(2 rows)

postgres=#

I hope you get the picture.

So, another good reason to choose Postgres (or for that matter EnterpriseDB) over Oracle... :)

PS: This works only with the B-Tree indexes though.