What business says does not mean what businees wants

This great sentence I learned form my exerience being a consultant

What business says does not mean what businees wants

TechEd 2010 in Eilat

Hi
I am going to attend TechEd 2010 in Eilat next week. It is great opportunity to learn new things , meet new and old friends.It is my second TechEd and I am will be focusing on Data Platform direction and BI. Hope to see you there.

http://www.microsoft.com/israel/TechEd2010/Tracks/BI.aspx

Blobs and covering indexes

Nowadays it is common to store/save pictures,documents in the databbase. Since SQL Server 2005 we use VARBINARY(MAX) datatype to store such data. The 'problem' I have seen recently at the client database is SELECT statement on very huge table that contain BLOB data and that data needs to be return to the client works pretty slowly. Run the below
SET STATISTICS IO ON

SELECT col1,col2, blobdata FROM tbl WHERE....

Table 'tbl'. Scan count 1, logical reads 8125, physical reads 0, read-ahead reads 0, lob logical reads 261521, lob physical reads 0, lob read-ahead reads 0.
CPU time = 1252 ms, elapsed time = 12632 ms.

We see high number of reads to return the data from index/blob pages.

Execution plan shows that there is Bookmark to return the BLOB data from Clustered Index Key because of our NCI(NonClustered Index) does not cover all columns in SELECT statement.
Ok, at first glance you would re-create NCI to INCLUDE blobdata column to 'cover' SELECT ...Well, I noticed that recreating NCI index takes long long time and LOG file was grown dramatically. I see that after INCLUDE blobdata column I reduced logical reads as shown below

Table 'tbl'. Scan count 1, logical reads 14, physical reads 0, read-ahead reads 0, lob logical reads 421521, lob physical reads 0, lob read-ahead reads 0.
CPU time = 1622 ms, elapsed time = 16512 ms.

But what happened? BLOB page reads were done almost 1.8 times more with covering index and actually I have not seen much improvment in performance of the query.
So finally, if you create an index or INCLUDE the BLOBs SQL Server create copy of that index for every blob column and thus it takes time to create index and reading the data from index page. Well, you were able to save some IO by covering BLOB column but internally SQL Server works much hardly to return the data and maintain the index.

Sometimes it is important to choose right collation for the server

The title looks like a joke, am I right? Sometimes we just take care of collation for specific database. Well that may lead you to unpleasant situation and moreover getting wrong or no data at all. Recently I helped my friend to solve the problem for his new software. He created a database with "right" collation let say Hebrew_CI_AS and the program searches for the data that contains hebrew characters. Suddenly the program does not return the data at all. He showed me that the data he is looking for are presented in the table and point me to the stored procedure that performs the searching. You have already guessed what was the problem, right? The problem was because withing a stored procedure he used a temporary table where the programm stores the data for final result (VARCHAR(n) for search string) for some logic. As you know tempdb is a system database which inherits a server's collation (SQL_Latin1_General_CP1_CI_AS) and hence no data were returned. In that specific case we changed the data type to NVARCHAR(n) and there is no need to reinstall the entire server, but think about the program(I have seen many of such) that such technique (store unicode character in temporary tables) are used in hundred of stored procedures and change the datatype for all of them is very big headache.

Window Functions (OVER Clause) – Help Make a Difference

Hello friends

As you probably know those days SQL Server 2011 is being developed. Itzik Ben-Gan believes (me too) that having those new window functions and enhance existing ones will benefit all of us SQL Server developers in the future more complete support for the standard window functions in SQL Server. Please read and vote..

http://www.sqlmag.com/blogs/puzzled-by-t-sql/tabid/1023/entryid/13085/Window-Functions-OVER-Clause-Help-Make-a-Difference.aspx

Be careful to grant dbCreator server role to the user

It is common that vendors ask for permission to create databases (or they applications need) on your servers and most of DBAs I have seen immediately grant them dbCreator server role. But they are not aware that members of that role are able to DROP/ALTER any databases on the entire server regardless of whether or not you even have a user account in the database.Did you really want that??

The right approach is to grant CREATE ANY DATABASE permission and then the user is able to DROP/ALTER he/she owns.

Another way to execute stored procedure

Just "discovered" that if you right click on the stored procedure you can clcik "Execute Stored Procedure" option. It gives you friendly GUI to provide parameters,however,as a data professional, I prefer to execute stored procedures in query builder. But it is nice feature for less experienced users.