Updated: Search Stored Procedures for Dependencies / References

In a discussion on the MSDN Forums I had posted my original code to search a Stored Procedure (search any object within SQL really) for specific text (http://social.msdn.microsoft.com/Forums/en-US/transactsql/thread/847b421d-332d-40f8-9649-b26fc2306920). You can view my original blog post describing this code block at: http://sqln.blogspot.com/2008/10/searching-text-of-programmable-objects.html.

Adam Haines had posted a wonderful enhancement to my T-SQL code. He had returned the matching text result as an XML instead of a text, this allows the user to click on the returned text and have the resulting text appear in a new window.

The new code, with the XML returned results, is:

DECLARE @StringToSearch NVARCHAR(MAX)
SET @StringToSearch = 'ENTER_SEARCH_TEXT_HERE'

SELECT    
    [name],   
    (   
        SELECT    
            OBJECT_DEFINITION(obj2.object_id) AS [text()]   
        from sys.all_objects obj2   
        where obj2.object_id = obj1.object_id   
        FOR XML PATH(''), TYPE   
    ) AS Obj_text,   
    [type] as ObjType    
FROM sys.all_objects obj1  
WHERE OBJECT_DEFINITION(object_id([name])) LIKE '%' + @StringToSearch + '%'
--Optional to limit search results....    
--AND [is_ms_shipped] = 0 --Only search user & post SQL release objects
--Change above to 1 if want to search only Microsoft provided objects released with SQL Server
--AND [type] = 'P' --Search only Stored Procedures
--AND [type] <> 'V' --Exclude Views
--See referenced article for listing of additional object types
--http://www.sqlservercentral.com/articles/T-SQL/63471/

Thanks again for this enhancement Adam!

Until next time, Happy Coding!!!

Books Online could be better...and we, the users, already can make it better!

Yesterday, Kalen Delaney wrote a small article discussing if MS should or shouldn't build in more warning messages or taking better actions in warning users about potential problems from performing tasks/commands within SQL Server. You can read her article at: http://www.sqlmag.com/Articles/ArticleID/101033/101033.html

I agree that to a certain extent the DBA is responsible for the database and should know how to use the software thoroughly...so ideally the database would never be at an unknown risk of data loss. Unfortunately, SQL Server has jumped from the realm of an application to the realm of a data platform! This changes things quite a bit; there is no realistic expectation that a single DBA (or even a small team of DBAs) can possibly know the database software and all of its commands and internal workings 100%. So there is some portion of relief that Microsoft must provide...rather it is a method of warning the DBA from messages, errors, or warnings I don't know or speculate a foreseeable method. I do agree that Books Online (BOL) is considered the SQL Server documentation and it is Microsoft's responsibility to ensure that the documentation provides all of the information (including inner workings where necessary) of commands and features that have potential unsafe effects.

The question is where does this responsibility end? Also, where does it fall onto the DBA (or end-user) shoulders to piece together all of this information and understand how they are utilizing the data platform and the data loss potential is created by this usage?

The first thing that comes to my mind is that Microsoft has taken a step in adding a way for the user's of BOL to add in their content that can point this type of stuff out. Why is it that we DBAs aren't doing this? I hope after reading this maybe our community will take a moment or two to place a useful comment (especially warning of potential data loss areas) in BOL for the other less knowledgeable DBAs.

Until next time, Happy Coding!

TSQL Code: Compare Tables of Databases on Separate Servers

NOTE: This script was originally developed to compare table row counts, but with the below mentioned modifications this could be helpful if you have a database that is shipped to another server and often times needs to be ETL into the other database and you are worried there may be records that aren't getting transferred properly (or at all).

The other day I came across a question on how to compare the tables in one database to the tables in another database, this was in concerns to a migration project. This person had a database that existed on an older server running SQL 2000 and they chose to migrate their database to a new server running SQL Server 2005. They had wanted to be able to somehow be able to visually display a comparison of the two databases to prove the conversion was successful, and also to display the comparisons of the tables. Results meeting above requirements are shown in Figure 1.

 
Figure 1 (results of running sp_CompareTables_All)

In response to this I had started to develop a TSQL script that created a stored procedure that would allow you to run it from the current database and specify the location of the original database. The script would then collect the tables and count the records within each table for both databases. It will display the table names on the outside (left and right) of the results, and the record counts will be next to each other on the inside (next to their table names); which will allow for a very simple and pleasing visual comparison. I wanted, and did, avoid using cursors or other techniques that will potentially bog down the system resources (such as the stored proc 'sp_MSForEachDB' and 'sp_MSForEachTable').

Now, this is a rough draft that I had thrown together and tested over a lunch period; so, there are some issues that can still be cleaned up on the script and it lacks the ability to detect if a table exists on one database, but not the other.

At the end of the script I'll also provide a quick comment that will allow you to change the results from displaying all tables and their row counts to display only the tables with mismatched row counts (which may be useful if you want to use this script as a method to troubleshoot databases that tend to not migrate all records).

The first problem faced is how to best access the server with the original database; while there are many options I chose to use the built-in stored procedure "sp_addlinkedserver". This procedure seems to be simple to implement and allows for seamless integration into TSQL code. Testing for this script was performed on the AdventureWorks database (developed for SQL 2005) on both test systems. The 'originating' database was on a SQL 2005 instance (although testing was briefly performed on SQL 2000 and SQL 2008 to validate compatibility). The 'originating' server is called TestServer35, the database is on an instance called Dev05; the database for both instances is called AdventureWorks2005. This information becomes important when using the sp_addlinkedserver command. I used the following TSQL code:

EXEC sp_addlinkedserver   
    @server='TestServer35-5', 
    @srvproduct='',
    @catalog='AdventureWorks2005',
    @provider='SQLNCLI', 
    @datasrc='Server35\Dev05'

 

As you can see, the linked server is referenced as TestServer35-5. We will use this reference, in a four-part identifier (Server.Catalog.Schema.Table). The next obstacle is to obtain a listing of tables and their row counts. I used a script I had modified last year to perform this since this script will run both on SQL 2005 and SQL 2000 (you can view my script on SQLServerCentral.com's Script section at: http://www.sqlservercentral.com/scripts/Administration/61766/). I then take the results of this and store them into a temporary table; I also do this for the new database (on local server where this stored proc is running at).

Then comes the simple part of joining the two temp tables into a final temp table. I chose this route because I wanted to have the two database in separate temp tables in the event I want to work with that data, which I will be working with the data in my update to determine if a table is missing from one of the databases.

Here is the TSQL code I used (remember if you want to use this you will need to change the linked server information to the correct information; as well as to create this stored proc in the appropriate database):

--Change the database name to the appropriate databse
USE [AdventureWorks2005];
GO

CREATE PROCEDURE sp_CompareTables_all
 AS
 
 CREATE TABLE #tblNew
( tblName varchar(50), CountRows int )

INSERT INTO #tblNew
( tblName, CountRows)
SELECT o.name AS "Table Name", i.rowcnt AS "Row Count"
FROM sysobjects o, sysindexes i
WHERE i.id = o.id
AND indid IN(0,1)
AND xtype = 'u'
AND o.name <> 'sysdiagrams'
ORDER BY o.name

CREATE TABLE #tblOLD
( tblName varchar(50), CountRows int )

INSERT INTO #tblOLD
( tblName, CountRows)
SELECT lo.name AS "Table Name", li.rowcnt AS "Row Count"
--********
--Replace TestServer35-5 and AdventureWorks2005 below with your appropriate values
--********
FROM [TestServer35-5].[AdventureWorks2005].[dbo].[sysobjects] lo, 
    [TestServer35-5].[AdventureWorks2005].[dbo].[sysindexes] li
WHERE li.id = lo.id
AND indid IN(0,1)
AND xtype = 'u'
AND lo.name <> 'sysdiagrams'
ORDER BY lo.name

CREATE TABLE #tblDiff
( OldTable varchar(50), OldRowCount int, NewRowCount int, NewTableName varchar(50))

INSERT INTO #tblDiff
( OldTable, OldRowCount, NewRowCount, NewTableName )
SELECT ol.tblName, ol.CountRows, nw.CountRows, nw.tblName
From    #tblNew nw
JOIN #tblOLD ol
ON (ol.tblName = nw.tblName AND ol.CountRows = nw.CountRows)
        
SELECT * FROM #tblDiff
        
DROP TABLE #tblNEW
DROP TABLE #tblOLD
DROP TABLE #tblDiff

 

You simply execute the code with the following TSQL:

EXECUTE sp_CompareTables_All

 

The results of this script are shown in Figure 1 (above).

Now, this is great if you want to have a list that you can go through yourself to verify each table matches in row counts. But, what if that database has 1000 or more tables? What if you are just, simply put, lazy? Why not utilize SQL Server to process this information for you?

Well, I sure enough did just that. With a very small modification to this script you can easily have it only display any tables that don't match up in record counts.

All you have to do is change the INSERT INTO #tblDiff block's "ON" statement to join if the CountRows are NOT equal. The following is the modified block of code; the remaining stored procedure remains the same:

ON (ol.tblName = nw.tblName AND ol.CountRows <> nw.CountRows)

 

I did also rename the stored procedure from "sp_CompareTables_All" to "sp_CompareTables_Diff", but this is optional for your own ability to clarify which stored proc is being used.

To get some results I had made a few modifications to the AdventureWorks2005 database. I had added a couple of rows to a table, and removed some rows from two tables. The results of the stored proc showing only the different tables are shown in Figure 2.

Figure 2 (results of running sp_CompareTables_Diff)

As you can see the ability to change this script to show all tables or only different tables is very simple. Even setting up this script is simple, where the hardest part of the whole thing is adding a linked server (which is fairly simple also).

In a future post I'll revisit this script and include the ability to display tables that exist on one database, but not in the other. Be sure to check back for this update.

Until next time...Happy Coding!!

SQL Server 2008 Officially RTM!

On August 11, 2008 Microsoft announced through their MSDN Flash newsletter that SQL Server 2008 has been RTM (Released To Manufacturing). This has been a long awaited release for many of us in the SQL community! Congratulations to Buck Woody and the many, many others on the SQL development team on this release!

While August 11, 2008 is probably the official RTM date, those of you that have an MSDN subscription may have been enjoying the RTM a week earlier (August 6th, 2008 through the MSDN Subscriptions website) as announced by Buck Woody's blog (Carpe Datum). You can view the post at: http://blogs.msdn.com/buckwoody/archive/2008/08/06/news-flass-sql-server-2008-is-here.aspx.

Undoubtedly, you can find many blogs and posts on the new features of SQL Server 2008. This looks to have a great improvement on SQL Server 2005; in just about every area. There is improvement on security, developing, and administering; to name a few. There seems to be a little bit of something for everyone to get excited about, ranging from Business Intelligence for the enterprise users to Intellisense in TSQL syntax for the programming DBA to Resource Governing for the IT Administrators.

I look forward to using SQL Server 2008, and to enjoying a little more easily administrated database with tons of new features, flexibility, and control!

Until next time...Happy Coding!

Publication: Introduction to the Transaction Log...

Today SQLServerCentral.com (SSC) had published my article that introduces the Transaction Log. The primary purpose of this article was to help the newer DBAs understand how the transaction log works, and to clarify some commonly misunderstood parts of maintaining the transaction log.

This article covers a very broad and general introduction; including how the log is filled by SQL Server, easy to follow analogies to help grasp how transaction logs work with SQL Server, and some Good Practices to use when Transaction Logs are in use by SQL Server.

You can read the entire article at: http://www.sqlservercentral.com/articles/Design+and+Theory/63350/

Please feel free to join in the discussion for this article; there are some great posts that help to further clarify the topic and also provides additional information that was not included with this article. You can join the discussion at: http://www.sqlservercentral.com/Forums/FindPost527448.aspx.

Listing User-Defined Stored Procedures in SQL Server 2005

You can easily obtain a listing of the User-Defined Stored Procedures that are in any of your databases. In fact, Microsoft had made this information very easily accessible. You only need to access a System Table view called "Sys.Procedures". This information may be easily accessed using a small TSQL code, such as the following...

USE [your_database_name_here];
GO
SELECT * FROM sys.procedures
ORDER BY [name];
GO

Your results will vary based on what Stored Procedures you or anyone else with access to your database have created. The following is a sample of the results I have obtained when running this code on my 'model' database.

The most important thing to keep in mind with this TSQL code is that each database may contain different User-Defined SPs.

Do you want to get a listing of EVERY single Stored Procedure in your database(s)? If so, then be sure to check out SQLServerCentral.com for one of my upcoming articles! I'll post the direct link to the article as soon as it becomes available!

You'll want to check this article out when it is published...you'll NEVER have to search the Internet again to find out what SPs are in SQL Server 2005!! UPDATE: You can read this article on SQLServerCentral.com (http://www.sqlservercentral.com/articles/T-SQL/63471/). Please leave feedback if you have a few moments.

TIP:

Do you want all of your databases you create (from here on...not previously created databases) to use a specified stored procedure or set of stored procedures? If so, then create the desired Stored Procedure(s) in your 'model' database. Now any new databases created will get the SP(s) you created in the 'model' database because your new databases are based on the 'model' database!

 

-----------------------

Legal Disclaimer/Warning

Please remember that when using an SP you are not sure the outcome or effect it has should be done on test systems; never use anything that has not been thoroughly tested in a production environment. I am not encouraging you to use any type of Stored Procedures (documented or undocumented); I am only informing you of the method that can be used to obtain a listing of all procedures that are found within SQL Server 2005. Microsoft strongly states that undocumented Stored Procedures, Extended Stored Procedures, functions, views, tables, columns, properties, or metadata are NOT to be used and do not have any associated support; and Microsoft Customer Support Services will not support any databases or applications that leverage or use any undocumented entry points. Please refer to: http://msdn.microsoft.com/en-us/library/ms166021.aspx for Microsoft's legal disclaimer and further information in Microsoft's support for use of stored procedures.

Optimizing Indexes

Summary:

Optimizing Indexes is quite a complicated subject. There are many techniques; and what is the most difficult is that there are so many different scenarios as to when and how to optimize your indexes. Instead of trying to describe a method of how to optimize, I am going to discuss how to identify when optimizing indexes should be considered and where to go to find the different options.

The first step is NOT to just rebuild all indexes, or to defrag them all. There are some people that believe that rebuilding all indexes is the way to solve this; don't listen to them!! PLEASE DON"T!!! I'm rarely the person to give advice on not listening to other people; most people can help you learn about what's good or bad...but if you go the route of rebuilding and defraging all your indexes, you can in fact be causing additional problems that you didn't have to cause. In particular using system resources that don't need to be used, and causing unneeded fragmentation on the OS level! Any decent DBA is always concerned with using system resources, remember that system resources is always a precious commodity and should never be wasted.

The first step is to analyze the database. The next step is to identify the queries that can/will benefit from optimizing the index(es). The third step is to optimize the index. The final step is to periodically review these methods to identify when optimizing indexes will be required; this will be an ongoing project and will ultimately require re-iterrating through your queries to identify when an index has become warranted for optimization. There is no cut and dry method to warn you, prevent indexes from becoming out of tune, or to auto-optimize the queries and indexes.

Analyzing the Database:

So, how do you analyze a database to determine if an index needs to be rebuilt or should run a defrag on the index? Well, first you need to understand how indexes are built and what is causing them to become fragmented. Review my blog entry "Introduction To Indexes" to learn about how indexes are built. Also, take the time to review this white paper called "Microsoft SQL Server 2000 Index Defragmentation Best Practices"; even though it is written for SQL Server 2000, it will still apply the same to SQL Server 2005. It is a long read, but will help out well beyond the scope of this blog entry.

Here, in a nutshell, is how to determine when your index is fragmented. Use SQL Profiler to identify poor performing queries; in particular use the template "SQLProfilerTSQL_Duration", this will already contain the traces needed to identify the offending queries. Once the queries are identified you can then start looking into which indexes there queries are accessing; especially queries that are retrieving ranges instead of singletons. These queries are the highest risk of having fragmented indexes, remember though that this is just a method to determine the potential problem areas. Your own judgement will be best to make the final determination.

When to Consider Optimizing Indexes:

The first key in detecting that you should optimize your index is when you are observing performance degradation and have no absolute culprit to cause this. Now, keep in mind that just because you are seeing performance degradation doesn't immediately indicate that there is index fragmentation. This can only be determined by analyzing your database properly. Next, identify which queries are utilizing the most I/O; these are the next candidates. Then consider queries that have workloads that are suspected to benefit from index defrags; this can be quite difficult and should be carefully determined.

All of these are covered in the MSDN white paper called "Microsoft SQL Server 2000 Index Defragmentation Best Practices"; mentioned earlier. This paper even goes into very good detail on how to make these determinations, which will probably be enough to get your through while you gain experience.

Getting Help:

Sometimes it's nice to have someone more experienced help out, if that is how you feel then go with that feeling and seek out that someone.

If you don't have physical access to an experienced DBA then seek advice from trusted websites, forums, and/or discussion groups. Remember when seeking advice they can only provide an answer with quality that matches the information you provided. Such as stating you have a database that needs indexes rebuilt or defragged, will most likely get you answers stating to use DBCC commands or some other commonly used index rebuilding command. The purpose of seeking advice is to provide detailed information to get an answer that is specific to your scenario; so be sure to provide as much information as possible without breaking any company policies.

Conclusion:

As you can see, Indexes can be fairly simple to optimize. It's determining when to optimize and what to optimize that becomes difficult.

There are methods to fine-tune the auto-index handling of your indexes, this is covered in the white paper I mention in the next section. You'll always find different opinions and experiences, embrace all you can and mix and match what works best for you and your situation. There is no one-size fits all for optimizing indexes, just as there isn't one-size fits all for database solutions. It's all about customizing to your needs, and utilizing your available resources to make your work easier and more enjoyable.

I can't stress enough that reading the "Microsoft SQL Server 2000 Index Defragmentation Best Practices" white paper will help out tremendously. This paper covers the topic so well, that originally I had planned on providing tips on how to identify the queries that required indexes to be rebuilt, and how to find additional help on this topic. During my research I came across this white paper and it covered absolutely everything and more than I had planned to cover!

Until next time, Happy Coding!!

Additional Resources:

Microsoft SQL Server 2000 Index Defragmentation Best Practices (http://www.microsoft.com/technet/prodtechnol/sql/2000/maintain/ss2kidbp.mspx)
SQL Server Best Practices (http://msdn.microsoft.com/en-us/sqlserver/bb671432.aspx)
How To: Optimize SQL Indexes (http://msdn.microsoft.com/en-us/library/ms979195.aspx)
Database Journal: Reducing SQL Server Index Fragmentation (http://www.databasejournal.com/features/mssql/article.php/2238211)
SQLServer Performance: SQL Server Index Fragmentation and Its Resolution (http://www.sql-server-performance.com/articles/per/index_fragmentation_p1.aspx)

Introduction To Indexes

Summary:

This is a basic introduction to what Indexes are and how to determine what should be indexed. I will cover the basic concept behind indexes, how they are intended to be helpful, why you would want to use them, and how to determine what should be included in your index.

I’ll also cover the differences between Clustered and Non-Clustered indexes, and provide some tips that will help you to know how to differentiate when to use which kind of index, as well as an analogy to break down the differences between Clustered and Non-Clustered indexes in simple terms.

What indexes are and why to use them:

Indexes are intended to help you to efficiently find information within your table; they are meant help you to lower the amount of CPU resources needed to find this information, and also to minimize the amount of Input/Output (I/O) used to access this information. All of this can result in a much faster result being returned.

Indexes in SQL Server can be thought of in a similar fashion as an index in the back of a book or a table of contents in the front of the book. In the book and Index is intended to allow you to specify a word that you are interested in finding and point you to the page(s) that word has been referenced. A Table Of Contents can be used to specify a topic you are interested in, and will point you to the section covering that topic; some table of contents will even point you to sub-sections that refine the context of the topic that can help you to more accurately focus your reading on relevant information.

Indexes within SQL Server are designed to perform these same functions, and provide the same helpful information. Indexes are created either through a T-SQL command or through a form of interface application that connects directly to the database and supports T-SQL commands (such as SQL Server Management Studio, or Enterprise Management, etc). NOTE: I will cover the topics of “Creating Indexes” and “Tuning Indexes” in separate blog entries. Once indexes are created SQL Server will automatically use them to ‘help’ in returning result sets; there are no options you must specify to take advantage of the created indexes…this is all built-in to SQL Server.

There are some minor differences in SQL Server 2000 and SQL Server 2005; since I primarily use SQL Server 2005 my discussion is based on this version. However, all of this information can be confirmed with the use of Books Online (BOL) for SQL Server 2000. I will try to avoid using specific information that can’t be used in SQL Server 2000; however, I am unable to guarantee that all information applies to previous SQL Server versions. Please use BOL if you are unsure of any of this information will work with your version of SQL Server.

How SQL Server Retrieves Data without Indexes:

Before we can go into how an index works, we should really understand how SQL Server finds data without the indexes; this will illustrate the importance of using Indexes. My examples will be based on a Customer Table that holds basic customer information such as the customer’s first and last name, their street address, city, state and zip code. When I use the term “Customer” I am referring to the Customer Table; this also goes for “First Name”, “Last Name”, etc. These are referencing their respective columns within the Customer Table.

What happens when SQL Server attempts to retrieve data from a table that does not contain any indexes is called a “Table Scan”. This is where SQL Server will go through each record (column by column, then row by row) to find matching records. After it has gone through the entire table it will return any matching results it has found. As you can probably image this is no quick task. This would be similar to picking up a book and deciding to find any pages that contain the word “alligator” in it. There might be a page with that word, there might now. In either case, without an index or table of contents you’d have to flip through every page to see if it contains this search word. If the book is under 30 pages, this may not be too bad…but, what if the book is 1500+ pages; that’s a whole different story.

This brings us to Indexes to help lower the amount of time SQL Server needs to spend finding matches in results!

Different Types of Indexes (and the general structure of an index):

There are two basic types of indexes: Clustered and Non-Clustered. Before I get into the specifics of each type and the differences between the types I want to cover the basic structure of an index; and the minor structural differences between the two types of indexes.

Basically all indexes are formulated with what is called “index key(s)” for a column (or combination of columns). These basically are pointers that tell SQL Server were specific words (or data) is contained within a table. Each table is broken into pages (this is physical storage of the data; each page is 8 KB and typically is constructed based on the order of entry…not a sort order). A page can contain hundreds of records, or just a few records. Because of the size limit in a data page, it all depends on the data types and how many columns are being stored for each record. There are formulas that can pin point the number of records being stored on a data page; this is beyond the scope of this blog entry.

Each index key(s) has a definition of the page the indexed word (or data) is stored. SQL Server will use these keys to determine what page to go to; so if the search term shows up in data page # 4 of 27 pages, SQL will skip over the first 3 pages and search page # 4. It will halt its search if there are no other keys specifying that data is stored in other pages; there are often times cases where data will be stored through multiple pages (like page #s 4, 12, 13, 21, 25, 26) or a data record could span multiple pages (such as page #4 & 5). Again, this is beyond the scope of this blog entry. The important thing to know is that data isn’t naturally stored in logical order within the physical file; this is why we need to have indexes to speed up the search. Also, since searches aren’t pre-determined when data is being entered SQL cannot have the data sorted, and in many cases you may have a specific method of sorting the data…but you might not be searching the sorted data (such as in Customer table, you might sort data based on customer’s location like City/State…but want to search for customer’s with Last Name starting with R; this type of a query and sort method can’t be pre-determined…hence the difficulty in storing data logically). Data is basically stored on a First In basis, and the rows just sequentially increase as data is entered, or removed. We need searches to tell us where the data is so that we can easily find this data to match our unknown (at entry time) search criteria and sorting methods.

This brings us to how do we tell SQL Server the best method to search if we don’t know it ourselves?! The answer is Clustered and Non-Clustered indexes, some research and knowledge of the data being stored, and a lot of testing (and refined Tuning as the database is used).

Clustered indexes:

Clustered indexes are a logical sorting and storing of index keys. This can allow SQL Server to very efficiently find data. This is all based on the defined columns within the clustered index. So, why don’t we want to just have every column within every table to be included in the clustered index? Because the more indexes included in the clustered index takes away from performance for your INSERTs, UPDATEs, and DELETE statements.

Basically the idea is that Indexes, especially Clustered, are wonderful to increase the speed to obtain results for Queries and Reports. However, there is a tradeoff which is that it takes more time write and/or modify data within the table. This is because the clustered index needs to update itself.

Imaging a file cabinet holding your customer information, you originally store all data by the customer’s Last name and then the First name. Now, you decide well, for getting information it would be quicker to store all of the data within each file by the date the data was added (and incase of similar dates then by alphabetical titles). So, now you need to find a customer John Smith and a paper that hold his Personal Address information…you look under Smith, find John, then in his folder look up Address section, then Personal and you quickly get the information.

Now, what if you have to update his file to include his birthdate, so that might go under Personal Information…not personal address though! So, now you find the last name, first name, then information section, then personal information page and add the file. Wouldn’t it have been quicker to just find his file and add her personal information to the end of his folder? That’s where the balance comes in, so question is partly how well your system performs with just reading queries/reports versus entering/modifying information…but the other part is what will be done more often. Are you going to query the information more often or are you going to update/modify the information more often? If you are querying, then siding on extra columns in your cluster MIGHT be ok; but if you are inserting/modifying data then you want only to use the number of columns it is to filter the result sets into manageable sections (maybe filter only name; last name, then first name…or maybe name and location; such as last name, first name, then city/state). It all just depends on what you are doing, how much data is being stored, and how you anticipate accessing this data will occur (i.e. often, seldom, with reports, lots of updates, lots of inserts, few inserts, etc).

Now, an important note is that you can ONLY have 1 clustered index per table! So, this can bring up the point of where you want the data to be accessible, but you don’t want to bog down the system each time you need to add/modify/delete data. So, how do you do this? How do you walk this fine line of optimal performance? Here come non-clustered indexes to the rescue!

Non-Clustered indexes:

You can have up to 249 Non-Clustered indexes; however, just as with Clustered Indexes there is such as thing as too many! Non-clustered indexes have its intended usage, which will get covered in the Tips section.

Non-Clustered indexes are indexes that aren’t sorted at the physical data page layer. This means that SQL Server can be pointed to the data page containing the data matching the search page; but the index stops after that point; it then becomes up to SQL to search that page and pick out the data. Remember Clustered Indexes point to the exact location of the data, and is quick because it is sorted. Non-Clustered indexes only point to the page; the Index Keys in the index are sorted also…but not the logical locations. So, there is some performance loss between Clustered and Non-Clustered. Always try to think of non-clustered indexes as an alternative to listing every column in a clustered index, and a method to allow for data that is less accessed or returns more Exact matched results.

So what does all of this mean? Well, basically if you were to tell SQL Server to find results of last names that start with ‘RE’ and used a non-clustered index to index the last name column then the index would point you to the page(s) that contain the last name(s) starting with “RE”, but there could be names also that start with “RA” or “RI” or “RH”, it all depends on what is actually stored at the time the query is executed. This then means that SQL would go through these other results until it finds the matching result; this is still faster than an entire table scan (which a table scan would start with Last Name “A” and End with Last Name “Z”).

Tips (putting this all together):

Now, that we have an understanding of what Clustered and Non-Clustered indexes are, and how SQL uses them let’s look at how we can determine what we should index (and what type of index to use). Remember:

• · A table can only have a single Clustered Index
• · Up to 249 non-clustered indexes
• · Clustered Indexes point to the exact location of matching results
• · Non-Clustered Indexes only point to the data page containing matching results, so some scanning will occur upon searching for matching results (however, much less scanning than not having any indexes)
• · Clustered Indexes can retrieve data much more efficiently; BUT have a cost of slower data INSERT, UPDATE, and DELETE
• · Non-Clustered indexes will use index key(s) if available, if none are available it will then use the data page ID or Row ID to perform its search for matching data

So now let’s put this all together into a simple understandable analogy. I will use a Library as our ‘database’, each section of the library (such as Romance, History, Computers, etc) will be our ‘Tables’, and of course each book will be our ‘record, or row’.

A catalog will contain two types of information. A ‘clustered’ catalog that will utilize the Dewey Decimal System; and is stored in the index box in Alphabetical Order by Book Title, followed by Author Name. A ‘non-clustered’ catalog will simply tell us the Section (‘Table’), the Shelf Number where top shelf is # 1 and bottom shelf is # 5 (This simulates our ‘data pages’), and finally the title of the book and the author (this is our First Name and Last Name columns). This is not sorted but does contain a listing of all book titles with Author Names that we can look at on a separate sheet to quickly get the index card # it is stored on.

Now with this in mind; imagine searching for a book called “James’ Awesome T-SQL Blog Book” by James R (no such book by the way exists). Now if we did this with a ‘clustered’ catalog. We could quickly look in the Title section and find the book that matches, if there were two books with this title we could then further define the result by looking at the author name.

Now imagine this same scenario but with the ‘non-clustered’ index. Let’s say the book title is somewhere around index card # 100 of 15000. Since we can quickly review the index cards listed we can see the card is around #100. So, we open the index drawer…we find our book information and now we are off.

Since the ‘clustered’ index card includes the Dewey Decimal System we can simply find the closest matching book numbered and quickly jump up or down as need to the exact book. Now with the ‘non-clustered’ index information we only know the section, title and shelf number. Now we get to the proper shelf, we then go through each book one at time to find the proper book. This of course is much quicker than starting at the beginning of the section and looking through each book, or even worse at the beginning of the first book in the library and sequentially going through the entire collection of books until we found the information (which may not even be there!).

Choosing Type of Index:

When to choose Clustered index and when to choose Non-Clustered indexes…

When to choose Clustered Indexes:

• · Columns that are frequently accessed
• · Columns intended to be stored sequentially (such as Last Name, First Name, etc)
• · Columns that will be queried in ranges (when you use WHERE clause with the BETWEEN, >, or < type of operators)

Once you have determined the columns that should be in your clustered index it then becomes ESPECIALLY CRITICAL to consider what type of queries will be ran most often and what queries MUST have optimal performance. If these columns are not within these queries then you may want to reconsider revising your clustered index NOT to include unnecessary columns (consider creating non-clustered index for these columns). If you find that you require columns within these queries that meet the above Index selection tips and they are not already included, and then consider revising your index to include these columns.

When to choose Non-Clustered Indexes:

• · Columns frequently in the WHERE clause that return EXACT matches
• · Columns that contain many distinct values (Such as Last Name, or Street Address; but not City, State or Zip Code).
• · Queries that do NOT return large result sets
• · Especially in columns that are needed for critical queries, and aren’t already covered in your Clustered Index; or may be queried in a non-sequential manner that isn’t already covered in your Clustered Index

Keep in mind that once you have created your Indexes, rather it be Clustered or Non-Clustered you can always revise them to meet your current needs. Also, remember that your needs will change and this often times will require revising your Indexes to meet those needs!

Conclusion:

Indexes are here to help you; however they are a complicated concept to master. In most cases it is easiest to figure out what columns qualify for being indexed and then to simply try them out. Don’t be afraid to try out a few different combinations of Clustered and Non-Clustered Indexes; performance is never a one size fits all. Your indexes should not be determined with that type of mind set.

I would also suggest setting a personal reminder or adding to your occasional checklist to check your indexes and how the table is accessing your indexes and to see if there is a way to improve the performance of your queries with the indexes for that table. Indexes will always be evolving, your queries will always be evolving, and your tables will always be evolving…don’t let me evolve without your intervention.

Remember that Speed = Happy Users…to me a Happy User = a Happy DBA! =)

Until next time, happy coding!

Types of backups

Overview:

There are different objects you can backup using SQL Server; in most cases when DBAs refer to backups they are referring to backing up databases. You can also backup the physical files and folders, but that will go beyond the scope of this blog posting. First I'll cover the three "Recovery Models" that you can choose for you database (Full, Simple, and Bulk-logged, respectively), then I'll cover the three different types of database backups: Full, Differential, and Transactions. Then I'll conclude with a quick overview of how to create backups for your database.

The most important thing to know is that you should always have a current backup in place that matches the needs of your company, you should have set procedures that detail how to backup your database and how to restore your database, and most importantly you should practice the database restoring plan you use (so you can verify it actually works, the data being backed up is actually being backed up, and that when the time comes for that once-in-a-lifetime emergency restore you will remain calm and collected so you can ensure the data is restored in a very prompt manner).

What is a backup? When do I make them?

Backups are copies of your database that is stored on your hard drive, on a server, on a removable media source, or any other type of location (physical and/or virtual). The basic idea behind a backup is to have a copy (or copies) of your data in a secure and easily obtainable location, and for the business critical information to have another copy stored somewhere offsite that is secure and obtained within a reasonable timeframe. Backups can contain all the information that is stored within your database, these are called "Full" backups. Most common backups contain entire copies of the database; there are also times when you will only retain copies that contain only the data that has been added since your last complete database backup. These are called "differential" and "transaction log" backups. Both accomplish the same thing in different ways and have different positives and negatives to them. I'll cover those later in this posting.

What you are aiming to accomplish is the ability to quickly recover from an incident that causes your current database to become corrupt or inoperable. Examples would be: Your database was hacked into the previous night, the database has somehow become corrupt and cannot be started, the data was accidentally deleted from a careless system maintenance procedure, or worse yet the building has been burned down or otherwise destroyed with all the computers and backups in it!

In most cases, you will access a backup copy that is stored in a secure location within your business location for the unforeseen events that can occur at any moment. In the extreme cases you will obtain your backup from your offsite location for the catastrophic events that require the business to be temporarily or permanently relocated without any prior notices.

So, now that we know what the backup is and where it is stored we now need to know when and how do we make them. The great thing about SQL, regardless of the version you get, you can make a backup at anytime. SQL uses online backup technology, so this means that your users and database can be accessing and modifying your database at anytime, even during your backup cycle! Do be aware that to create a backup takes up some resources, such as CPU, Memory, and I/O. It is most common to make backups during the business' "down cycle"; usually in the middle of the night for traditional 9-5 companies...and the 24x7 companies that are always accessing data will require a little more planning by determining the data usage trends and adjusting the backup procedures to occur during the lowest peaks or generalized time frame that matches the expected lower usage peaks.

Recovery Models:

There are three recovery models that can be chosen at the time you create your database: Full, Simple, and Bulk-logged. Each database can have it's own recovery model; and this recovery model may be changed from within the database in a future time.

Full: This model allows you to recover your database to a specific point in time, or to the point of the failure. This model will record every transaction that occurs within your database, as well as the stored data, structure, and every other object; this includes the bulk operations and bulk loading of data. For this model you will typically want to use Full and Differential backup types at a minimum; to maintain a more complete backup solution you would also use the Transaction Log backup type.

Simple: This model will allow you to recover to the point of your last backup creation; it's very important to understand that this model does NOT allow the use of Transaction Log backups. This model uses the 'TRUNCATE LOG ON CHECKPOINT' option; which in effect deletes all old transactions when the database gets to a checkpoint. This is more ideal for system databases because the transaction log is deleted at each checkpoint.

Bulk-logged: Bulk operations and bulk loads are logged at the most minimal levels. This means that during a restore you will need to repeat the bulk operations and bulk loading of data, should the database fail prior to a Full backup or a Differential backup. The ideal strategy will implement the Full and Differential backup types at a minimum, and include Transaction Log backups on a regular re-occurrence. 

Types of Backups:

I'll clarify now that I am discussing using the SQL Server Management Studio (SSMS) backup options; and that there are many different methods to create backups, but this discussion is limited to performing file backups using the BACKUP syntax & wizards. Some other options that are commonly used, but are beyond the scope of this posting, are: Log Shipping, High Availability (i.e. Redundancy hard drive configurations, standby servers, etc), and many others using a combination of hardware/software solutions.

The three types of backups that can be accessed from within SSMS are: Full, Differential, and Transaction Log. Here is a brief breakdown of each type:

Full
Creates a backup that contains all objects, system tables and data from the database, it also includes portions of the transaction log that required because of database being used at the time the backup was created. A Full backup is intended to bring you right back to complete working order up to the point in time the backup was created.

Differential
This type of backup is designed to create a backup of only the objects, tables and data (including transaction logs) that have been changed or not recorded on the last Full backup. It is very important to understand that you can NOT create a differential backup until after you have created at least 1 full backup.

On a personal observation note: you'll notice that a Differential is quite a bit faster than the Full backup because it requires less information to be created and is recording much less information, however, as with everything else there is a trade off. If you choose to create only 1 Full backup and then from there on use Differential backups to save time and resources, you will have to use all of these Differential files to restore to the last point of your Differential backup. What I'm saying here is that assume you make a daily Differential every single day for the next 2 years; on the first day of the 3rd year you have a database failure and must restore the database. You will have to first restore the Full backup file you originally made and then you will have restore all 730 Differential files.

You can choose to create a Full backup at anytime and it will automatically replace your original Full backup and ALL differential backups made between the original Full backup and the current Full backup you are making.

Transaction Log
Transaction Logs are a special type that compliment the Full and Differential backup types. These are serialized records of all database modifications made since the last transaction log backup. They are used during the recovery process to roll-back or commit transactions. Unlike the Full and Differential backups, Transaction Logs backups are recording the state of the transaction log at the START of the backup operation. Transaction Logs are best to think of a way you can have backed up checkpoints between the time you have made your last Full or Differential backup. A most common method of use is in OLTP databases that have daily Differential backups and weekly Full backups; you would use the Transaction Log backup on an hourly basis to help minimize the lost of transactions in case of a failure within the middle of the day. It is very common to be used with live websites that have many transactions occur per hour; instead of losing a full days worth of transactions you can minimize it down to an hour, or in highly volatile situations could even get down to the seconds (however, it is very uncommon to have a transaction log backup on a per second basis).

How do I make a backup?

In SSMS you can easily create a backup of your database by right-clicking on your database and selecting "Tasks" then "Back Up...". This will open the "Back Up Database" dialog box that allows you to easily fill in the appropriate information and then either have SSMS perform the backup, or create a script using the scripting wizard from within the "Back Up Database" dialog box.

From the "Back Up Database" dialog box you can choose the backup type, the name of the backup file, the location to place the file (including using devices that contain the file location and other information). By click on "Options" in the left pane, you will be brought to another screen that will allow you to give even more specific options for your backups. Some options include creating a new set of backups, appending to an existing set, verifying the backup reliability, and for transaction logs you can specify how to handle the log after being backed up.

Conclusion:

As you can tell, the backup options and wizard are each powerful in their own rights. I can't stress enough the importance of having a backup plan and a recovery plan in place now, it can save you time and also provide you with the confidence that you know when a disaster occurs you are ready and have reliable backups that can be restored in an instance.

You have now seen that backups can cover most any situation that you can come across, and depending on the need can back up a database down to the second in the highest volatile uses.

This is just the tipping of the iceberg, there are many vendors out there that specialize in create backup/recovery solutions that are based on software, hardware, and hardware/software combinations.

With some careful planning, execution and understanding you can handle any situation that will cross your path and know that in the worse of conditions you are prepared to get your business back up and running faster than they can get a grasp on what just happened to their business!

Until next time....Happy Coding!

BACKUP (Transact-SQL)

This is a simple reference to the "Backup" T-SQL syntax. This syntax is probably one of the most simple, complicated and yet important syntaxes to know.

It's simple because you have a few different options, first you can use SQL Server Management Studio to do your complete backup (full, differential, and transactional). You can also create a backup using the T-SQL syntax directly and it is quite simple even though the below T-SQL syntax can make it look scarier.

Here's an example of a very simple T-SQL backup (you can find more at the link to the MSDN Books Online reference below the syntax):

DATABASE   AdventureWorks   TO   DISK   = 'Z:\SQLServerBackups\AdvWorksData.bak'   WITH   FORMAT ; GO

It's complex because...well, just look at the full syntax! It can get to be very complex if you want to enable a lot of features; and this can be a very, very good thing if you need to leverage power when the SSMS wizards/built-in tools just can't give you what you want.

It's important because...well, I hope you already know this. If you don't have a backup and something happens to your data, then you are up a creek without a paddle and just about starting to go over the Niagara Falls! If you ever hear someone tell you that you are backing up too frequently or you are overkill on backups, then I'd simply walk away from that person as quickly as possible. If you value your position, and don't want to be the one to explain to the owner (or your boss) why it is that at 4 AM the system went down and the $100,000 in transactions didn't get saved because you are only backing up daily instead of after EVERY transaction then make sure you understand backups, how to restore, and what different options are available to you.

Ok, enough of the CYA talk. Now lets get to the syntax. As mentioned already, it looks scary and complicated. Hopefully, with the above example of 1 usage you will see that it is simple to use. The thing to keep in mind is that Microsoft is providing all of your backup needs rolled into 1 command. So this means that there are many options you won't use unless you are doing a differential backup, likewise with full and transactional backups.

Keep your backups fresh..treat them like Milk..don't let one sit around for too long without checking it, and...

Replace your backups on a regular basis!

Until next time...happy coding!

SQL Server 2005 Books Online (September 2007)

BACKUP (Transact-SQL)

Updated: 1 February 2007

Backs up a complete database, or one or more files or filegroups (BACKUP DATABASE). Also, under the full recovery model or bulk-logged recovery model, backs up the transaction log (BACKUP LOG).

Transact-SQL Syntax Conventions

Syntax

Backing Up a Whole Database  BACKUP DATABASE { database_name | @database_name_var }   TO <backup_device> [ ,...n ]   [ <MIRROR TO clause> ] [ next-mirror-to ]   [ WITH { DIFFERENTIAL | <general_WITH_options> [ ,...n ] } ]
[;]

Backing Up Specific Files or Filegroups
BACKUP DATABASE { database_name | @database_name_var }  <file_or_filegroup> [ ,...n ]   TO <backup_device> [ ,...n ]   [ <MIRROR TO clause> ] [ next-mirror-to ]   [ WITH { DIFFERENTIAL | <general_WITH_options> [ ,...n ] } ]
[;]

Creating a Partial Backup
BACKUP DATABASE { database_name | @database_name_var }  READ_WRITE_FILEGROUPS [ , <read_only_filegroup> [ ,...n ] ]   TO <backup_device> [ ,...n ]   [ <MIRROR TO clause> ] [ next-mirror-to ]   [ WITH { DIFFERENTIAL | <general_WITH_options> [ ,...n ] } ]
[;]

Backing Up the Transaction Log (full and bulk-logged recovery models)
BACKUP LOG { database_name | @database_name_var }   TO <backup_device> [ ,...n ]   [ <MIRROR TO clause> ] [ next-mirror-to ]   [ WITH { <general_WITH_options> | <log-specific_optionspec> } [ ,...n ] ]
[;]

Truncating the Transaction Log (breaks the log chain) 
BACKUP LOG { database_name | @database_name_var }   WITH { NO_LOG | TRUNCATE_ONLY } 
[;]

<backup_device>::=  {    { logical_device_name | @logical_device_name_var }  | { DISK | TAPE } =      { 'physical_device_name' | @physical_device_name_var }  } 

<MIRROR TO clause>::=  MIRROR TO <backup_device> [ ,...n ]

<file_or_filegroup>::=  {    FILE = { logical_file_name | @logical_file_name_var }  | FILEGROUP = { logical_filegroup_name | @logical_filegroup_name_var }  } 

<read_only_filegroup>::=
FILEGROUP = { logical_filegroup_name | @logical_filegroup_name_var }

<general_WITH_options> [ ,...n ]::= 
--Backup Set Options       COPY_ONLY   | DESCRIPTION = { 'text' | @text_variable }  | NAME = { backup_set_name | @backup_set_name_var }  | PASSWORD = { password | @password_variable }  | [ EXPIREDATE = { date | @date_var }         | RETAINDAYS = { days | @days_var } ]  | NO_LOG 

--Media Set Options    { NOINIT | INIT }  | { NOSKIP | SKIP }  | { NOFORMAT | FORMAT }  | MEDIADESCRIPTION = { 'text' | @text_variable }  | MEDIANAME = { media_name | @media_name_variable }  | MEDIAPASSWORD = { mediapassword | @mediapassword_variable }  | BLOCKSIZE = { blocksize | @blocksize_variable } 

--Data Transfer Options    BUFFERCOUNT = { buffercount | @buffercount_variable }  | MAXTRANSFERSIZE = { maxtransfersize | @maxtransfersize_variable }

--Error Management Options    { NO_CHECKSUM | CHECKSUM }  | { STOP_ON_ERROR | CONTINUE_AFTER_ERROR }

--Compatibility Options    RESTART 

--Monitoring Options    STATS [ = percentage ] 

--Tape Options    { REWIND | NOREWIND }  | { UNLOAD | NOUNLOAD } 

--Log-specific Options    { NORECOVERY | STANDBY = undo_file_name }  | NO_TRUNCATE

BACKUP (Transact-SQL)

Getting Started – Transact-SQL (T-SQL)

Overview:

This blog is aimed to help you get started using T-SQL. T-SQL is a syntax used in SQL Server; it generally composes of the majority work that is performed in the SQL database to get the data, store the data and/or work with the data. There are various other aspects of SQL Server that are used to perform many tasks that will be covered in other blogs; you'll find that in fact many of the tools used to setup new databases, new users, and other operations/tasks within SQL Server are nothing more than a nice Graphical User Interface (GUI) based on T-SQL commands.

What is T-SQL?

T-SQL, as already mentioned, is the syntax you will use to directly interact with the data stored within your database. T-SQL is typically entered via a GUI tool or application. A typical Database Administrator (DBA) might use Microsoft's SQL Server Management Studio (SSMS) or Enterprise Manager (EM) to enter T-SQL statements. A typical Database Programmer (DBP) might use a programming language such as Visual Basic or C# to enter T-SQL statements.

A common T-SQL statement used, almost in every instance of obtaining data information, is the "SELECT" statement. This statement can be a simple one or very complex. A typical usage may be:

    SELECT * FROM table1

This example would select all data from all columns from a table called "table1". This would be the simplest of all possible examples; but you aren't limited to only this single use. You can create complex SELECT statements that can calculate multiple fields and return the results, could join multiple tables, you could even join tables (or columns) from other databases!

How Do I use T-SQL?

T-SQL is used by entering a line of text within the chosen editor and then executing the command(s) within the SQL Server environment. A DBA may use SSMS to directly enter the commands within the SQL Server environment, or he/she may create a series of commands stored within a file (this is commonly referred to as a 'script') that can later be executed, or he/she may create a stored procedure that holds these commands within the SQL Server environment that can be later called by utilizing the "EXECUTE" keyword.

The important thing to know isn't how to use T-SQL; it's how to find the information to learn how to do what you want with T-SQL. I could spend this whole blog, and many more, on just how to use the SELECT statement; I could spend a lifetime blogging on how to use every T-SQL command there is within SQL Server (and before I even could get through half those commands and new version of SQL Server would appear causing us to restart the learning process!). As the famous saying goes: "Give a person a fish and they eat for a day; teach the person to fish and they eat for the rest of their lives". SQL Server is no different. So, I'm going to concentrate on how to find the information you need.

Where do I find the information I need?

This is actually quite simple to answer…the internet! But, if you want really detailed information that provides you with ALL of the information on how to use ANY (and all) T-SQL commands there is only one place you can go. NO, not this blog…you'd go straight to the horse's mouth; MSDN website. In particular you go to: Transact-SQL Reference (this URL is listed in the "Additional References" section at the end of this blog). This is the pillar to the T-SQL commands; everything starts there! When you first go there you are welcomed with a small page telling you what Transact-SQL is and how it is used; but, that's not the great part yet. The great part is (at the time of this blog) that to the left is a pane (navigation listing) that will list ALL of the T-SQL commands. You can even access other SQL Server reference information from here!

You'll also find many other additional resources on the internet. Microsoft contains a section called "Community" this will provide links to their forums, newsgroups and other websites; I highly recommend reviewing this section and discovering what is contained within these links. Outside of Microsoft there are many, many, hundreds of thousands of websites that cover SQL Server, T-SQL and/or anything to do with databases.

My favorite sites can be found in the "Resources" section of the main page of my blog; this doesn't mean I endorse or agree with these sites…I find that I frequent these sites on an almost daily basis. This listing may change and you are welcome to check back periodically. I also welcome any other suggestions of websites that you may find you can't live without..Please leave a comment to this posting and I'll be sure to make it available to all of the readers.

What books, training or other materials do you suggest?

Well, that is very objectionable. There seems to be no one book that covers all topics; most books targeted at beginner/intermediate users will focus on most popular areas of SQL Server and a good book will make you aware of other areas that exist but are not covered by that book. In regards to T-SQL in particular, I'd recommend for the beginning user to get a book such as SAMS 'Teach yourself Microsoft SQL Server T-SQL in 10 minutes'; this covers the most commonly used T-SQL commands and leads you progressively with each lesson.

I, personally, enjoy the Microsoft Press series for detailed information if I know a particular subject I want to learn about. I also have found that SAMS has other titles that cover a large spectrum of topics and are usually worth looking into.

It all comes down to taste, objective and personal preference. I still, without any doubt, always recommend keeping Books Online handy and using the MSDN website; you'll find most of the answers right there already; the answers you don't find can usually be asked (and receive quick responses) in the forums within the MSDN website.

Conclusion:

There is no single source of reference or answer for SQL Server; you will find that Microsoft has gone to great lengths to provide you with the knowledge and means to gain the knowledge to use SQL Server. If you find that Microsoft doesn't offer what you need then there are many other sites readily available to provide you with that information. Learning is everything!

Additional References

Transact-SQL Reference: http://msdn2.microsoft.com/en-us/library/ms189826.aspx