SQL performance slowing down

I was working on a database since last couple of month. Suddenly it was slowing down day by day. I had not changes anything in the database. 

Then I checked the database properties and found that recovery model was set to Full. 
Full recovery model was not needed as I do not use incremental backup. 
So I set recovery model to Simple and my problem is solved.

Change Database compatibility level

You can change the database compatibility level through Management Studio. (Go to Database Properties - Option).

Here is the script to change the database compatibility level through SQL:

ALTER DATABASE <DB_Name> SET SINGLE_USER 
GO 
EXEC sp_dbcmptlevel <DB_Name>, 100; 
GO 
ALTER DATABASE <DB_Name> SET MULTI_USER 
GO

In above script change <DB_Name> with Database Name (you want to change the compatibility level).

Compatibility Level :

SQL Server 2008 : 100
SQL Server 2005 : 90
SQL Server 2000 : 80
SQL Server 7.0 : 70

ACID rule of thumb for transactions

A transaction must be:

1. Atomic - It is one unit of work and does not dependent on previous and following transactions.
2. Consistent - Data is either committed or roll back, no ?in-between? case where something has been updated and something hasn't.
3. Isolated - no transaction sees the intermediate results of the current transaction).
4. Durable - the values persist if the data had been committed even if the system crashes right after.

Query to get All Databases Size

User below query to find Database Size :

SELECT  d.name AS [Database Name],

        ROUND(SUM(mf.size) * 8 / 1024, 0) [Size (MB)]

FROM    sys.master_files mf

        INNER JOIN sys.databases d ON d.database_id = mf.database_id

WHERE   d.database_id > 4 

GROUP BY d.name 

ORDER BY d.name

Database Engine Tuning Adviser not found

Today, I want to optimize some some queries. I searched the net and found that we can use Database Engine Tuning Adviser for this. But I could not found that in SSMS. 

Again I searched the net and found that it is not available with SQL server express edition.

So I uninstalled the SQL Server Express Edition and  installed SQL Server Developer Edition. 

Now I got the Database Engine Tuning Adviser