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• SQL SERVER – master Database Log File Grew Too Big

  - by pinaldave

  Couple of the days ago, I received following email and I find this email very interesting and I feel like sharing with all of you. Note: Please read the whole email before providing your suggestions. “Hi Pinal, If you can share these details on your blog, it will help many. We understand the value of the master database and we take its regular back up (everyday midnight). Yesterday we noticed that our master database log file has grown very large. This is very first time that we have encountered such an issue. The master database is in simple recovery mode; so we assumed that it will never grow big; however, we now have a big log file. We ran the following command USE [master] GO DBCC SHRINKFILE (N'mastlog' , 0, TRUNCATEONLY) GO We know this command will break the chains of LSN but as per our understanding; it should not matter as we are in simple recovery model.     After running this, the log file becomes very small. Just to be cautious, we took full backup of the master database right away. We totally understand that this is not the normal practice; so if you are going to tell us the same, we are aware of it. However, here is the question for you? What operation in master database would have caused our log file to grow too large? Thanks, [name and company name removed as per request]“ Here was my response to them: “Hi [name removed], It is great that you are aware of all the right steps and method. Taking full backup when you are not sure is always a good practice. Regarding your question what could have caused your master database log to grow larger, let me try to guess what could have happened. Do you have any user table in the master database? If yes, this is not recommended and also NOT a good practice. If have user tables in master database and you are doing any long operation (may be lots of insert, update, delete or rebuilding them), then it can cause this situation. You have made me curious about your scenario; do revert back. Kind Regards, Pinal” Within few minutes I received reply: “That was it Pinal. We had one of the maintenance task log tables created in the master table, which had many long transactions during the night. We moved it to newly created database named ‘maintenance’, and we will keep you updated.” I was very glad to receive the email. I do not suggest that any user table should be created in the master database. It should be left alone from user objects. Now here is the question for you – can you think of any other reason for master log file growth? Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Backup and Restore, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• SQL SERVER – Changing Default Installation Path for SQL Server

  - by pinaldave

  Earlier I wrote a blog post about SQL SERVER – Move Database Files MDF and LDF to Another Location and in the blog post we discussed how we can change the location of the MDF and LDF files after database is already created. I had mentioned that we will discuss how to change the default location of the database. This way we do not have to change the location of the database after it is created at different locations. The ideal scenario would be to specify this default location of the database files when SQL Server Installation was performed. If you have already installed SQL Server there is an easy way to solve this problem. This will not impact any database created before the change, it will only affect the default location of the database created after the change. To change the default location of the SQL Server Installation follow the steps mentioned below: Go to Right Click on Servers >> Click on Properties >> Go to the Database Settings screen You can change the default location of the database files. All the future database created after the setting is changed will go to this new location. You can also do the same with T-SQL and here is the T-SQL code to do the same. USE [master] GO EXEC xp_instance_regwrite N'HKEY_LOCAL_MACHINE', N'Software\Microsoft\MSSQLServer\MSSQLServer', N'DefaultData', REG_SZ, N'F:\DATA' GO EXEC xp_instance_regwrite N'HKEY_LOCAL_MACHINE', N'Software\Microsoft\MSSQLServer\MSSQLServer', N'DefaultLog', REG_SZ, N'F:\DATA' GO What are the best practices do you follow with regards to default file location for your database? I am interested to know them. Reference : Pinal Dave (http://blog.SQLAuthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Server Management Studio, SQL Tips and Tricks, T SQL, Technology

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• SQLAuthority News – List of Master Data Services White Paper

  - by pinaldave

  Since my TechEd India 2010 presentation I am very excited with SQL Server 2010 MDS. I just come across very interesting white paper on Microsoft site related to this subject. Here is the list of the same and location where you can download them. They are all written by Top Experts at Microsoft. Master Data Management from a Business Perspective - Download a PDF version or an XPS version Master Data Management from a Technical Perspective - Download a PDF version or an XPS version Bringing Master Data Management to the Stakeholders - Download a PDF version or an XPS version Implementing a Phased Approach to Master Data Management - Download a PDF version or an XPS version SharePoint Workflow Integration with Master Data Services - Read it here. Reference : Pinal Dave (http://blog.SQLAuthority.com) Filed under: SQL, SQL Authority, SQL Documentation, SQL Download, SQL Query, SQL Server, SQL Tips and Tricks, SQL White Papers, T SQL

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• SQL SERVER – Script to Find First Day of Current Month

  - by Pinal Dave

  Earlier I wrote a blog post about SQL SERVER – Query to Find First and Last Day of Current Month and it is a very popular post. In this post, I convert the datetime to Varchar and later on use it. However, SQL Expert Michael Usov has made a good point suggesting that it is not always a good idea to convert datetime to any other date format as it is quite possible that we may need it the value in the datetime format for other operation. He has suggested a very quick solution where we can get the first day of the current month with or without time value and keep them with datatype datetime. Here is the simple script for the same. -- first day of month -- with time zeroed out SELECT CAST(DATEADD(DAY,-DAY(GETDATE())+1, CAST(GETDATE() AS DATE)) AS DATETIME) -- with time as it was SELECT DATEADD(DAY,-DAY(GETDATE())+1, CAST(GETDATE() AS DATETIME)) Here is the resultset: Reference: Pinal Dave (http://blog.SQLAuthority.com)Filed under: PostADay, SQL, SQL Authority, SQL DateTime, SQL Function, SQL Query, SQL Server, SQL Tips and Tricks, T SQL

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• SQL SERVER – Difference Between CURRENT_TIMESTAMP and GETDATE() – CURRENT_TIMESTAMP Equivalent in SQL Server

  - by pinaldave

  A common question – I often get from Oracle/MySQL Professionals: “What is the Equivalent to CURRENT_TIMESTAMP in SQL Server?” Here is a common question I often get from SQL Server Professionals: “What are differences between Difference Between CURRENT_TIMESTAMP and GETDATE ()?” Very simple question but have showed up so frequently that I feel like to write about it. Well in SQL Server GETDATE() is Equivalent to CURRENT_TIMESTAMP. However, if you use CURRENT_TIMESTAMP in your select statement it will work fine. You can see in the above example – both of them returns the same value. Now let us go to next question regarding difference between GETDATE and CURRENT_TIMESTAMP. Well, the matter of the fact, there is no difference between them in SQL Server (Reference Link). CURRENT_TIMESTAMP is an ANSI SQL function, whereas GETDATE is T-SQL implementation of the same function. Both of them derive value from the operating system of the computer on which SQL Server instance is running. Above discussion prompts another question – in this case, what should one use GETDATE or CURRENT_TIMESTAMP? Well, this is indeed tricky and interesting question. I think I am very comfortable using the GETDATE () so I will go to use it but a matter of the fact there is no right or wrong answer. If you want to follow ancient saying “When in Rome, do as the Romans do”, I suggest using the GETDATE (), or continue using CURRENT_TIMESTAMP. With that said, there is one very important property we all need to keep in mind. If you use CURRENT_TIMESTAMP while creating an object, they are automatically converted to GETDATE() and stored internally. To illustrate what I am suggesting here is the example - Create a table using the following script CREATE TABLE [dbo].[TestTable]( [Cold2] [datetime] NULL ) ON [PRIMARY] GO ALTER TABLE [dbo].[TestTable] ADD DEFAULT (CURRENT_TIMESTAMP) FOR [Cold2] GO Now go to SSMS and generate the script for the table and you will notice following syntax. CREATE TABLE [dbo].[TestTable]( [Cold2] [datetime] NULL ) ON [PRIMARY] GO ALTER TABLE [dbo].[TestTable] ADD DEFAULT (GETDATE()) FOR [Cold2] GO You can notice that SQL Server have automatically converted CURRENT_TIMESTAMP to GETDATE(). I guess this gives us an idea how they behave. Now go ahead and make your choice! Do let me know which one will you use CURRENT_TIMESTAMP or GETDATE () in the comments area. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL DateTime, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• SQL SERVER – Puzzle to Win Print Book – Functions FIRST_VALUE and LAST_VALUE with OVER clause and ORDER BY

  - by pinaldave

  Some time an interesting feature and smart audience makes total difference at places. From last two days, I have been writing on SQL Server 2012 feature FIRST_VALUE and LAST_VALUE. Please read following post before I continue today as this question is based on the same. Introduction to FIRST_VALUE and LAST_VALUE Introduction to FIRST_VALUE and LAST_VALUE with OVER clause As a comment of the second post I received excellent question from Nilesh Molankar. He asks what will happen if we change few things in the T-SQL. I really like this question as this kind of questions will make us sharp and help us perform in critical situation in need. We recently publish SQL Server Interview Questions book. I promise that in future version of this book, we will for sure include this question. Instead of repeating his question, I am going to ask something very similar to his question. Let us first run following query (read yesterday’s blog post for more detail): USE AdventureWorks GO SELECT s.SalesOrderID,s.SalesOrderDetailID,s.OrderQty, FIRST_VALUE(SalesOrderDetailID) OVER (PARTITION BY SalesOrderID ORDER BY SalesOrderDetailID ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) FstValue, LAST_VALUE(SalesOrderDetailID) OVER (PARTITION BY SalesOrderID ORDER BY SalesOrderDetailID ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) LstValue FROM Sales.SalesOrderDetail s WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ORDER BY s.SalesOrderID,s.SalesOrderDetailID,s.OrderQty GO Here is the resultset of the above query. Now let us change the ORDER BY clause of OVER clause in above query and see what is the new result. USE AdventureWorks GO SELECT s.SalesOrderID,s.SalesOrderDetailID,s.OrderQty, FIRST_VALUE(SalesOrderDetailID) OVER (PARTITION BY SalesOrderID ORDER BY OrderQty ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) FstValue, LAST_VALUE(SalesOrderDetailID) OVER (PARTITION BY SalesOrderID ORDER BY OrderQty ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) LstValue FROM Sales.SalesOrderDetail s WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ORDER BY s.SalesOrderID,s.SalesOrderDetailID,s.OrderQty GO Now let us see the result and ready for interesting question: Puzzle You can see that row number 2, 3, 4, and 5 has same SalesOrderID = 43667. The FIRST_VALUE is 78 and LAST_VALUE is 77. Now if these function was working on maximum and minimum value they should have given answer as 77 and 80 respectively instead of 78 and 77. Also the value of FIRST_VALUE is greater than LAST_VALUE 77. Why? Explain in detail. Hint Let me give you a simple hint. Just for simplicity I have changed the order of columns selected in the SELECT and ORDER BY (at the end). This will not change resultset but just order of the columns as well order of the rows. However, the data remains the same. USE AdventureWorks GO SELECT s.OrderQty,s.SalesOrderID,s.SalesOrderDetailID, FIRST_VALUE(SalesOrderDetailID) OVER (PARTITION BY SalesOrderID ORDER BY OrderQty ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) FstValue, LAST_VALUE(SalesOrderDetailID) OVER (PARTITION BY SalesOrderID ORDER BY OrderQty ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) LstValue FROM Sales.SalesOrderDetail s WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ORDER BY s.OrderQty,s.SalesOrderID,s.SalesOrderDetailID GO Above query returns following result: Now I am very sure all of you have figured out the solution. Here is the second hint – pay attention to row 2, 3, 4, and 10. Hint2 T-SQL Enhancements: FIRST_VALUE() and LAST_VALUE() MSDN: FIRST_VALUE and LAST_VALUE Rules Leave a comment with your detailed answer by Nov 15′s blog post. Open world-wide (where Amazon ships books) If you blog about puzzle’s solution and if you win, you win additional surprise gift as well. Prizes Print copy of my new book SQL Server Interview Questions Amazon|Flipkart If you already have this book, you can opt for any of my other books SQL Wait Stats [Amazon|Flipkart|Kindle] and SQL Programming [Amazon|Flipkart|Kindle]. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Function, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• SQL SERVER – Fix: Error: File cannot be loaded because the execution of scripts is disabled on this system. Please see “get-help about_signing” for more details

  - by pinaldave

  Yesterday I formatted my computer and did fresh install as it was due from long time. After the fresh install when I tried to install Semantic Search application using powershell, I was stopped by following error. File cannot be loaded because the execution of scripts is disabled on this system. Please see “get-help about_signing” for more details Fix/Solution/Workaround: The solution is very simple. Open the Powershell window and type following two lines and everything will fine right after that. Set-ExecutionPolicy Unrestricted Set-ExecutionPolicy RemoteSigned Again, this is I have done for my environment where I am very careful what I will run. You can change the policy back to original restricted policy if you want to restrict future execution of the powershell scripts. Simple – isn’t it? Well all complex looking problems are very simple to solve. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Error Messages, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology Tagged: Powershell

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• SQL SERVER – Guest Post – Glenn Berry – Wait Type – Day 26 of 28

  - by pinaldave

  Glenn Berry works as a Database Architect at NewsGator Technologies in Denver, CO. He is a SQL Server MVP, and has a whole collection of Microsoft certifications, including MCITP, MCDBA, MCSE, MCSD, MCAD, and MCTS. He is also an Adjunct Faculty member at University College – University of Denver, where he has been teaching since 2000. He is one wonderful blogger and often blogs at here. I am big fan of the Dynamic Management Views (DMV) scripts of Glenn. His script are extremely popular and the reality is that he has inspired me to start this series with his famous DMV which I have mentioned in very first  wait stats blog post (I had forgot to request his permission to re-use the script but when asked later on his whole hearty approved it). Here is is his excellent blog post on this subject of wait stats: Analyzing cumulative wait stats in SQL Server 2005 and above has become a popular and effective technique for diagnosing performance issues and further focusing your troubleshooting and diagnostic  efforts.  Rather than just guessing about what resource(s) that SQL Server is waiting on, you can actually find out by running a relatively simple DMV query. Once you know what resources that SQL Server is spending the most time waiting on, you can run more specific queries that focus on that resource to get a better idea what is causing the problem. I do want to throw out a few caveats about using wait stats as a diagnostic tool. First, they are most useful when your SQL Server instance is experiencing performance problems. If your instance is running well, with no indication of any resource pressure from other sources, then you should not worry that much about what the top wait types are. SQL Server will always be waiting on some resource, but many wait types are quite benign, and can be safely ignored. In spite of this, I quite often see experienced DBAs obsessing over the top wait type, even when their SQL Server instance is running extremely well. Second, I often see DBAs jump to the wrong conclusion based on seeing a particular well-known wait type. A good example is CXPACKET waits. People typically jump to the conclusion that high CXPACKET waits means that they should immediately change their instance-level MADOP setting to 1. This is not always the best solution. You need to consider your workload type, and look carefully for any important “missing” indexes that might be causing the query optimizer to use a parallel plan to compensate for the missing index. In this case, correcting the index problem is usually a better solution than changing MAXDOP, since you are curing the disease rather than just treating the symptom. Finally, you should get in the habit of clearing out your cumulative wait stats with the  DBCC SQLPERF(‘sys.dm_os_wait_stats’, CLEAR); command. This is especially important if you have made an configuration or index changes, or if your workload has changed recently. Otherwise, your cumulative wait stats will be polluted with the old stats from weeks or months ago (since the last time SQL Server was started or the stats were cleared).  If you make a change to your SQL Server instance, or add an index, you should clear out your wait stats, and then wait a while to see what your new top wait stats are. At any rate, enjoy Pinal Dave’s series on Wait Stats. This blog post has been written by Glenn Berry (Twitter | Blog) Read all the post in the Wait Types and Queue series. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, Readers Contribution, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, SQL Wait Stats, SQL Wait Types, T SQL, Technology

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• SQL SERVER – Fastest Way to Restore the Database

  - by pinaldave

  A few days ago, I received following email: “Pinal, We are in an emergency situation. We have a large database of around 80+ GB and its backup is of 50+ GB in size. We need to restore this database ASAP and use it; however, restoring the database takes forever. Do you think a compressed backup would solve our problem? Any other ideas you got?” First of all, the asker has already answered his own question. Yes; I have seen that if you are using a compressed backup, it takes lesser time when you try to restore a database. I have previously blogged about the same subject. Here are the links to those blog posts: SQL SERVER – Data and Page Compressions – Data Storage and IO Improvement SQL SERVER – 2008 – Introduction to Row Compression SQL SERVER – 2008 – Introduction to New Feature of Backup Compression However, if your database is very large that it still takes a few minutes to restore the database even though you use any of the features listed above, then it will really take some time to restore the database. If there is urgency and there is no time you can spare for restoring the database, then you can use the wonderful tool developed by Idera called virtual database. This tool restores a certain database in just a few seconds so it will readily be available for usage. I have in depth written my experience with this tool in the article here SQL SERVER – Retrieve and Explore Database Backup without Restoring Database – Idera virtual database. Let me know your experience in this scenario. Have you ever needed your database backup restored very quickly, what did you do in that scenario. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, Readers Question, SQL, SQL Authority, SQL Backup and Restore, SQL Performance, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• SQLAuthority News – Fast Track Data Warehouse 3.0 Reference Guide

  - by pinaldave

  http://msdn.microsoft.com/en-us/library/gg605238.aspx I am very excited that Fast Track Data Warehouse 3.0 reference guide has been announced. As a consultant I have always enjoyed working with Fast Track Data Warehouse project as it truly expresses the potential of the SQL Server Engine. Here is few details of the enhancement of the Fast Track Data Warehouse 3.0 reference architecture. The SQL Server Fast Track Data Warehouse initiative provides a basic methodology and concrete examples for the deployment of balanced hardware and database configuration for a data warehousing workload. Balance is measured across the key components of a SQL Server installation; storage, server, application settings, and configuration settings for each component are evaluated. Description Note FTDW 3.0 Architecture Basic component architecture for FT 3.0 based systems. New Memory Guidelines Minimum and maximum tested memory configurations by server socket count. Additional Startup Options Notes for T-834 and setting for Lock Pages in Memory. Storage Configuration RAID1+0 now standard (RAID1 was used in FT 2.0). Evaluating Fragmentation Query provided for evaluating logical fragmentation. Loading Data Additional options for CI table loads. MCR Additional detail and explanation of FTDW MCR Rating. Read white paper on fast track data warehousing. Reference: Pinal Dave (http://blog.SQLAuthority.com)   Filed under: Business Intelligence, Data Warehousing, PostADay, SQL, SQL Authority, SQL Documentation, SQL Download, SQL Query, SQL Server, SQL Tips and Tricks, SQL White Papers, SQLAuthority News, T SQL, Technology

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• SQL SERVER – Installing Data Quality Services (DQS) on SQL Server 2012

  - by pinaldave

  Data Quality Services is very interesting enhancements in SQL Server 2012. My friend and SQL Server Expert Govind Kanshi have written an excellent article on this subject earlier on his blog. Yesterday I stumbled upon his blog one more time and decided to experiment myself with DQS. I have basic understanding of DQS and MDS so I knew I need to start with DQS Client. However, when I tried to find DQS Client I was not able to find it under SQL Server 2012 installation. I quickly realized that I needed to separately install the DQS client. You will find the DQS installer under SQL Server 2012 >> Data Quality Services directory. The pre-requisite of DQS is Master Data Services (MDS) and IIS. If you have not installed IIS, you can follow the simple steps and install IIS in your machine. Once the pre-requisites are installed, click on MDS installer once again and it will install DQS just fine. Be patient with the installer as it can take a bit longer time if your machine is low on configurations. Once the installation is over you will be able to expand SQL Server 2012 >> Data Quality Services directory and you will notice that it will have a new item called Data Quality Client.  Click on it and it will open the client. Well, in future blog post we will go over more details about DQS and detailed practical examples. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, SQL Utility, T SQL, Technology Tagged: Data Quality Services

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• SQL SERVER – 2014 CTP1 Available for Download – SQL SERVER 2014 Community Technology Preview 1

  - by Pinal Dave

  Microsoft announced that SQL Server 2014 CTP 1 available to download at TechEd Europe. You can download SQL Server 2014 CTP1 from here. Additionally, there is in depth documentation of the product in the Product Guide over here. In this blog post I have in depth discussed what are the salient features which I was looking forward in the new version. Always On supports now 8 secondaries instead of 4 Online Indexing at partition level – this is a good thing as now index rebuilding can be done at a partition level Statistics at the partition level – this will be a huge improvement in performance In-Memory OLTP works by providing in-application memory storage for the most often used tables in SQL Server. Columnstore Index can be updated – I just can’t wait for this feature (Columnstore Index) Resource Governor can control IO along with CPU and Memory Increase performance by extending SQL Server in-memory buffer pool to SSDs Backup to Azure Storage You can read about the new features of the SQL Server 2014 in the following links: What’s New (Database Engine) What’s New in Analysis Services and Business Intelligence What’s New (Integration Services) What’s New (Replication) What’s New (Reporting Services) Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Service Pack, SQL Tips and Tricks, T SQL, Technology Tagged: CTP

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• SQLAuthority News – 2 Whitepapers Announced – AlwaysOn Architecture Guide: Building a High Availability and Disaster Recovery Solution

  - by pinaldave

  Understanding AlwaysOn Architecture is extremely important when building a solution with failover clusters and availability groups. Microsoft has just released two very important white papers related to this subject. Both the white papers are written by top experts in industry and have been reviewed by excellent panel of experts. Every time I talk with various organizations who are adopting the SQL Server 2012 they are always excited with the concept of the new feature AlwaysOn. One of the requests I often here is the related to detailed documentations which can help enterprises to build a robust high availability and disaster recovery solution. I believe following two white paper now satisfies the request. AlwaysOn Architecture Guide: Building a High Availability and Disaster Recovery Solution by Using AlwaysOn Availability Groups SQL Server 2012 AlwaysOn Availability Groups provides a unified high availability and disaster recovery (HADR) solution. This paper details the key topology requirements of this specific design pattern on important concepts like quorum configuration considerations, steps required to build the environment, and a workflow that shows how to handle a disaster recovery. AlwaysOn Architecture Guide: Building a High Availability and Disaster Recovery Solution by Using Failover Cluster Instances and Availability Groups SQL Server 2012 AlwaysOn Failover Cluster Instances (FCI) and AlwaysOn Availability Groups provide a comprehensive high availability and disaster recovery solution. This paper details the key topology requirements of this specific design pattern on important concepts like asymmetric storage considerations, quorum model selection, quorum votes, steps required to build the environment, and a workflow. If you are not going to implement AlwaysOn feature, this two Whitepapers are still a great reference material to review as it will give you complete idea regarding what it takes to implement AlwaysOn architecture and what kind of efforts needed. One should at least bookmark above two white papers for future reference. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Documentation, SQL Download, SQL Query, SQL Server, SQL Tips and Tricks, SQL White Papers, T SQL, Technology Tagged: AlwaysOn

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• SQL SERVER – How to See Active SQL Server Connections For Database

  - by Pinal Dave

  Another question received via email - “How do I I know which user is connected to my database with how many connection?” Here is the script which will give us answer to the question. SELECT DB_NAME(dbid) AS DBName, COUNT(dbid) AS NumberOfConnections, loginame FROM    sys.sysprocesses GROUP BY dbid, loginame ORDER BY DB_NAME(dbid) Here is the resultset: Reference: Pinal Dave (http://blog.SQLAuthority.com)Filed under: PostADay, SQL, SQL Authority, SQL DMV, SQL Query, SQL Server, SQL Tips and Tricks, T SQL

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• SQL SERVER – Introduction to SQL Server 2014 In-Memory OLTP

  - by Pinal Dave

  In SQL Server 2014 Microsoft has introduced a new database engine component called In-Memory OLTP aka project “Hekaton” which is fully integrated into the SQL Server Database Engine. It is optimized for OLTP workloads accessing memory resident data. In-memory OLTP helps us create memory optimized tables which in turn offer significant performance improvement for our typical OLTP workload. The main objective of memory optimized table is to ensure that highly transactional tables could live in memory and remain in memory forever without even losing out a single record. The most significant part is that it still supports majority of our Transact-SQL statement. Transact-SQL stored procedures can be compiled to machine code for further performance improvements on memory-optimized tables. This engine is designed to ensure higher concurrency and minimal blocking. In-Memory OLTP alleviates the issue of locking, using a new type of multi-version optimistic concurrency control. It also substantially reduces waiting for log writes by generating far less log data and needing fewer log writes. Points to remember Memory-optimized tables refer to tables using the new data structures and key words added as part of In-Memory OLTP. Disk-based tables refer to your normal tables which we used to create in SQL Server since its inception. These tables use a fixed size 8 KB pages that need to be read from and written to disk as a unit. Natively compiled stored procedures refer to an object Type which is new and is supported by in-memory OLTP engine which convert it into machine code, which can further improve the data access performance for memory –optimized tables. Natively compiled stored procedures can only reference memory-optimized tables, they can’t be used to reference any disk –based table. Interpreted Transact-SQL stored procedures, which is what SQL Server has always used. Cross-container transactions refer to transactions that reference both memory-optimized tables and disk-based tables. Interop refers to interpreted Transact-SQL that references memory-optimized tables. Using In-Memory OLTP In-Memory OLTP engine has been available as part of SQL Server 2014 since June 2013 CTPs. Installation of In-Memory OLTP is part of the SQL Server setup application. The In-Memory OLTP components can only be installed with a 64-bit edition of SQL Server 2014 hence they are not available with 32-bit editions. Creating Databases Any database that will store memory-optimized tables must have a MEMORY_OPTIMIZED_DATA filegroup. This filegroup is specifically designed to store the checkpoint files needed by SQL Server to recover the memory-optimized tables, and although the syntax for creating the filegroup is almost the same as for creating a regular filestream filegroup, it must also specify the option CONTAINS MEMORY_OPTIMIZED_DATA. Here is an example of a CREATE DATABASE statement for a database that can support memory-optimized tables: CREATE DATABASE InMemoryDB ON PRIMARY(NAME = [InMemoryDB_data], FILENAME = 'D:\data\InMemoryDB_data.mdf', size=500MB), FILEGROUP [SampleDB_mod_fg] CONTAINS MEMORY_OPTIMIZED_DATA (NAME = [InMemoryDB_mod_dir], FILENAME = 'S:\data\InMemoryDB_mod_dir'), (NAME = [InMemoryDB_mod_dir], FILENAME = 'R:\data\InMemoryDB_mod_dir') LOG ON (name = [SampleDB_log], Filename='L:\log\InMemoryDB_log.ldf', size=500MB) COLLATE Latin1_General_100_BIN2; Above example code creates files on three different drives (D:  S: and R:) for the data files and in memory storage so if you would like to run this code kindly change the drive and folder locations as per your convenience. Also notice that binary collation was specified as Windows (non-SQL). BIN2 collation is the only collation support at this point for any indexes on memory optimized tables. It is also possible to add a MEMORY_OPTIMIZED_DATA file group to an existing database, use the below command to achieve the same. ALTER DATABASE AdventureWorks2012 ADD FILEGROUP hekaton_mod CONTAINS MEMORY_OPTIMIZED_DATA; GO ALTER DATABASE AdventureWorks2012 ADD FILE (NAME='hekaton_mod', FILENAME='S:\data\hekaton_mod') TO FILEGROUP hekaton_mod; GO Creating Tables There is no major syntactical difference between creating a disk based table or a memory –optimized table but yes there are a few restrictions and a few new essential extensions. Essentially any memory-optimized table should use the MEMORY_OPTIMIZED = ON clause as shown in the Create Table query example. DURABILITY clause (SCHEMA_AND_DATA or SCHEMA_ONLY) Memory-optimized table should always be defined with a DURABILITY value which can be either SCHEMA_AND_DATA or  SCHEMA_ONLY the former being the default. A memory-optimized table defined with DURABILITY=SCHEMA_ONLY will not persist the data to disk which means the data durability is compromised whereas DURABILITY= SCHEMA_AND_DATA ensures that data is also persisted along with the schema. Indexing Memory Optimized Table A memory-optimized table must always have an index for all tables created with DURABILITY= SCHEMA_AND_DATA and this can be achieved by declaring a PRIMARY KEY Constraint at the time of creating a table. The following example shows a PRIMARY KEY index created as a HASH index, for which a bucket count must also be specified. CREATE TABLE Mem_Table ( [Name] VARCHAR(32) NOT NULL PRIMARY KEY NONCLUSTERED HASH WITH (BUCKET_COUNT = 100000), [City] VARCHAR(32) NULL, [State_Province] VARCHAR(32) NULL, [LastModified] DATETIME NOT NULL, ) WITH (MEMORY_OPTIMIZED = ON, DURABILITY = SCHEMA_AND_DATA); Now as you can see in the above query example we have used the clause MEMORY_OPTIMIZED = ON to make sure that it is considered as a memory optimized table and not just a normal table and also used the DURABILITY Clause= SCHEMA_AND_DATA which means it will persist data along with metadata and also you can notice this table has a PRIMARY KEY mentioned upfront which is also a mandatory clause for memory-optimized tables. We will talk more about HASH Indexes and BUCKET_COUNT in later articles on this topic which will be focusing more on Row and Index storage on Memory-Optimized tables. So stay tuned for that as well. Now as we covered the basics of Memory Optimized tables and understood the key things to remember while using memory optimized tables, let’s explore more using examples to understand the Performance gains using memory-optimized tables. I will be using the database which i created earlier in this article i.e. InMemoryDB in the below Demo Exercise. USE InMemoryDB GO -- Creating a disk based table CREATE TABLE dbo.Disktable ( Id INT IDENTITY, Name CHAR(40) ) GO CREATE NONCLUSTERED INDEX IX_ID ON dbo.Disktable (Id) GO -- Creating a memory optimized table with similar structure and DURABILITY = SCHEMA_AND_DATA CREATE TABLE dbo.Memorytable_durable ( Id INT NOT NULL PRIMARY KEY NONCLUSTERED Hash WITH (bucket_count =1000000), Name CHAR(40) ) WITH (MEMORY_OPTIMIZED = ON, DURABILITY = SCHEMA_AND_DATA) GO -- Creating an another memory optimized table with similar structure but DURABILITY = SCHEMA_Only CREATE TABLE dbo.Memorytable_nondurable ( Id INT NOT NULL PRIMARY KEY NONCLUSTERED Hash WITH (bucket_count =1000000), Name CHAR(40) ) WITH (MEMORY_OPTIMIZED = ON, DURABILITY = SCHEMA_only) GO -- Now insert 100000 records in dbo.Disktable and observe the Time Taken DECLARE @i_t bigint SET @i_t =1 WHILE @i_t<= 100000 BEGIN INSERT INTO dbo.Disktable(Name) VALUES('sachin' + CONVERT(VARCHAR,@i_t)) SET @i_t+=1 END -- Do the same inserts for Memory table dbo.Memorytable_durable and observe the Time Taken DECLARE @i_t bigint SET @i_t =1 WHILE @i_t<= 100000 BEGIN INSERT INTO dbo.Memorytable_durable VALUES(@i_t, 'sachin' + CONVERT(VARCHAR,@i_t)) SET @i_t+=1 END -- Now finally do the same inserts for Memory table dbo.Memorytable_nondurable and observe the Time Taken DECLARE @i_t bigint SET @i_t =1 WHILE @i_t<= 100000 BEGIN INSERT INTO dbo.Memorytable_nondurable VALUES(@i_t, 'sachin' + CONVERT(VARCHAR,@i_t)) SET @i_t+=1 END The above 3 Inserts took 1.20 minutes, 54 secs, and 2 secs respectively to insert 100000 records on my machine with 8 Gb RAM. This proves the point that memory-optimized tables can definitely help businesses achieve better performance for their highly transactional business table and memory- optimized tables with Durability SCHEMA_ONLY is even faster as it does not bother persisting its data to disk which makes it supremely fast. Koenig Solutions is one of the few organizations which offer IT training on SQL Server 2014 and all its updates. Now, I leave the decision on using memory_Optimized tables on you, I hope you like this article and it helped you understand  the fundamentals of IN-Memory OLTP . Reference: Pinal Dave (http://blog.sqlauthority.com)Filed under: PostADay, SQL, SQL Authority, SQL Performance, SQL Query, SQL Server, SQL Tips and Tricks, T SQL Tagged: Koenig

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• SQL SERVER – SQL in Sixty Seconds – Last Three Episodes – Need Your Opinion

  - by Pinal Dave

  I have been blogging for almost 7 years and building video content for around 2 years. After spending so much time on blogging and creating video, I have got the quite a good idea what people would like to read and what people like to watch. However, there is one thing, which I am constantly struggling after almost a year and I would like to get your opinion about it. Though, this may look very simple to you but it is very crucial to me and I would like to know your opinion about it. I have been building video almost every week for my SQL in Sixty Seconds series and it has been quite popular. So far on my YouTube Channel there are over 2600 subscribers and over 250K views. Here is my problem – there are about 50+ videos on SQL in Sixty Seconds Series but the not every video is popular. There are a few videos which are extremely popular and there are videos which are absolutely struggling to get even single view. I have yet not figured out what people would love to watch on this channel. I noticed lots of people watching various videos but hardly anyone leaving comments or suggestions. At the end of the blog posts associated with the SQL in Sixty Seconds, I always ask which video people would love to watch, but I get a very low response over there too. What I wonder is that why such a low engagement of viewers/readers on the video blog posts where as the channel is success and lots of people are watching the video? What do you think I should change in my video to increase the engagement? Here are my last three videos from SQL in Sixty Seconds channel and I would like to know your feedback. Remove Cached Login from SSMS Connect Dialog – SQL in Sixty Seconds #049 RESEED Identity Column in Database Table – SQL in Sixty Seconds #051 Puzzle SET ANSI_NULLS and Resultset – SQL in Sixty Seconds #052  The feedback which I will like the most will for sure get a special surprise gift for me. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL in Sixty Seconds, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology, Video

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• SQL SERVER – A Puzzle – Swap Value of Column Without Case Statement

  - by pinaldave

  For the last few weeks, I have been doing Friday Puzzles and I am really loving it. Yesterday I received a very interesting question by Navneet Chaurasia on Facebook Page. He was asked this question in one of the interview questions for job. Please read the original thread for a complete idea of the conversation. I am presenting the same question here. Puzzle Let us assume there is a single column in the table called Gender. The challenge is to write a single update statement which will flip or swap the value in the column. For example if the value in the gender column is ‘male’ swap it with ‘female’ and if the value is ‘female’ swap it with ‘male’. Here is the quick setup script for the puzzle. USE tempdb GO CREATE TABLE SimpleTable (ID INT, Gender VARCHAR(10)) GO INSERT INTO SimpleTable (ID, Gender) SELECT 1, 'female' UNION ALL SELECT 2, 'male' UNION ALL SELECT 3, 'male' GO SELECT * FROM SimpleTable GO The above query will return following result set. The puzzle was to write a single update column which will generate following result set. There are multiple answers to this simple puzzle. Let me show you three different ways. I am assuming that the column will have either value ‘male’ or ‘female’ only. Method 1: Using CASE Statement I believe this is going to be the most popular solution as we are all familiar with CASE Statement. UPDATE SimpleTable SET Gender = CASE Gender WHEN 'male' THEN 'female' ELSE 'male' END GO SELECT * FROM SimpleTable GO Method 2: Using REPLACE  Function I totally understand it is the not cleanest solution but it will for sure work in giving situation. UPDATE SimpleTable SET Gender = REPLACE(('fe'+Gender),'fefe','') GO SELECT * FROM SimpleTable GO Method 3: Using IIF in SQL Server 2012 If you are using SQL Server 2012 you can use IIF and get the same effect as CASE statement. UPDATE SimpleTable SET Gender = IIF(Gender = 'male', 'female', 'male') GO SELECT * FROM SimpleTable GO You can read my article series on SQL Server 2012 various functions over here. SQL SERVER – Denali – Logical Function – IIF() – A Quick Introduction SQL SERVER – Detecting Leap Year in T-SQL using SQL Server 2012 – IIF, EOMONTH and CONCAT Function Let us clean up. DROP TABLE SimpleTable GO Question to you: I came up with three simple tricks where there is a single UPDATE statement which swaps the values in the column. Do you know any other simple trick? If yes, please post here in the comments. I will pick two random winners from all the valid answers. Winners will get 1) Print Copy of SQL Server Interview Questions and Answers 2) Free Learning Code for Online Video Courses I will announce the winners on coming Monday. Reference:  Pinal Dave (http://blog.SQLAuthority.com) Filed under: CodeProject, PostADay, SQL, SQL Authority, SQL Interview Questions and Answers, SQL Puzzle, SQL Query, SQL Server, SQL Tips and Tricks, SQLServer, T SQL, Technology

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• SQLAuthority News – Best Practices for Data Warehousing with SQL Server 2008 R2

  - by pinaldave

  An integral part of any BI system is the data warehouse—a central repository of data that is regularly refreshed from the source systems. The new data is transferred at regular intervals  by extract, transform, and load (ETL) processes. This whitepaper talks about what are best practices for Data Warehousing. This whitepaper discusses ETL, Analysis, Reporting as well relational database. The main focus of this whitepaper is on mainly ‘architecture’ and ‘performance’. Download Best Practices for Data Warehousing with SQL Server 2008 R2 Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Best Practices, Data Warehousing, PostADay, SQL, SQL Authority, SQL Documentation, SQL Download, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• SQL SERVER – Integration Services Balanced Data Distributor – SSIS Balanced Data Distributor

  - by pinaldave

  Microsoft SSIS Balanced Data Distributor (BDD) is a new SSIS transform. This transform takes a single input and distributes the incoming rows to one or more outputs uniformly via multithreading. The transform takes one pipeline buffer worth of rows at a time and moves it to the next output in a round robin fashion. It’s balanced and synchronous so if one of the downstream transforms or destinations is slower than the others, the rest of the pipeline will stall so this transform works best if all of the outputs have identical transforms and destinations. Download SQL Server Integration Services Balanced Data Distributor Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Documentation, SQL Download, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• SQL SERVER – BI Quiz – Troubleshooting Cube Performance

  - by pinaldave

  My friend Jacob Sebastian runs SQL BI Quiz competition. Where there are 30 different questions on each day of the month. Winners get opportunity to participate in this Quiz, learn something new and win great awards. Working with huge data is very common when it is about Data Warehousing. It is necessary to create Cubes on the data to make it meaningful and consumable. There are cases when retrieving the data from cube takes lots of the time. Let us assume that your cube is returning you data very quickly. Suddenly on one day it is returning the data very slowly. What are the three things will you in order to diagnose this. After diagnose what you will do to resolve performance issue. Participate in my question over here Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Business Intelligence, Pinal Dave, PostADay, Readers Question, SQL, SQL Authority, SQL Performance, SQL Puzzle, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• SQL SERVER – Download Free eBook – Introducing Microsoft SQL Server 2012

  - by pinaldave

  Database Administration and Business Intelligence is indeed very key area of the SQL Server. My very good friend Ross Mistry and Stacia Misner has recently wrote book which is for SQL Server 2012. The best part of the book is it is totally FREE! Well, this book assumes that you have certain level of SQL Server Administration as well Business Intelligence understanding. So if you are absolutely beginner I suggest you read other books of Ross as well attend Pluralsight course of Stacia Misner. Personally I read this book in last 10 days and I find it very easy to read and very comprehensive as well. Part I Database Administration (by Ross Mistry) 1. SQL Server 2012 Editions and Engine Enhancements 2. High-Availability and Disaster-Recovery Enhancements 3. Performance and Scalability 4. Security Enhancements 5. Programmability and Beyond-Relational Enhancements Part II Business Intelligence Development (by Stacia Misner) 6. Integration Services 7. Data Quality Services 8. Master Data Services 9. Analysis Services and PowerPivot 10. Reporting Services Here are various versions of the eBook. PDF ePub Mobi Amazon Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Database, PostADay, SQL, SQL Authority, SQL Download, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• SQL SERVER – Get All the Information of Database using sys.databases

  - by pinaldave

  Earlier I wrote blog article SQL SERVER – Finding Last Backup Time for All Database. In the response of this article I have received very interesting script from SQL Server Expert Matteo as a comment in the blog. He has written script using sys.databases which provides plenty of the information about database. I suggest you can run this on your database and know unknown of your databases as well. SELECT database_id, CONVERT(VARCHAR(25), DB.name) AS dbName, CONVERT(VARCHAR(10), DATABASEPROPERTYEX(name, 'status')) AS [Status], state_desc, (SELECT COUNT(1) FROM sys.master_files WHERE DB_NAME(database_id) = DB.name AND type_desc = 'rows') AS DataFiles, (SELECT SUM((size*8)/1024) FROM sys.master_files WHERE DB_NAME(database_id) = DB.name AND type_desc = 'rows') AS [Data MB], (SELECT COUNT(1) FROM sys.master_files WHERE DB_NAME(database_id) = DB.name AND type_desc = 'log') AS LogFiles, (SELECT SUM((size*8)/1024) FROM sys.master_files WHERE DB_NAME(database_id) = DB.name AND type_desc = 'log') AS [Log MB], user_access_desc AS [User access], recovery_model_desc AS [Recovery model], CASE compatibility_level WHEN 60 THEN '60 (SQL Server 6.0)' WHEN 65 THEN '65 (SQL Server 6.5)' WHEN 70 THEN '70 (SQL Server 7.0)' WHEN 80 THEN '80 (SQL Server 2000)' WHEN 90 THEN '90 (SQL Server 2005)' WHEN 100 THEN '100 (SQL Server 2008)' END AS [compatibility level], CONVERT(VARCHAR(20), create_date, 103) + ' ' + CONVERT(VARCHAR(20), create_date, 108) AS [Creation date], -- last backup ISNULL((SELECT TOP 1 CASE TYPE WHEN 'D' THEN 'Full' WHEN 'I' THEN 'Differential' WHEN 'L' THEN 'Transaction log' END + ' – ' + LTRIM(ISNULL(STR(ABS(DATEDIFF(DAY, GETDATE(),Backup_finish_date))) + ' days ago', 'NEVER')) + ' – ' + CONVERT(VARCHAR(20), backup_start_date, 103) + ' ' + CONVERT(VARCHAR(20), backup_start_date, 108) + ' – ' + CONVERT(VARCHAR(20), backup_finish_date, 103) + ' ' + CONVERT(VARCHAR(20), backup_finish_date, 108) + ' (' + CAST(DATEDIFF(second, BK.backup_start_date, BK.backup_finish_date) AS VARCHAR(4)) + ' ' + 'seconds)' FROM msdb..backupset BK WHERE BK.database_name = DB.name ORDER BY backup_set_id DESC),'-') AS [Last backup], CASE WHEN is_fulltext_enabled = 1 THEN 'Fulltext enabled' ELSE '' END AS [fulltext], CASE WHEN is_auto_close_on = 1 THEN 'autoclose' ELSE '' END AS [autoclose], page_verify_option_desc AS [page verify option], CASE WHEN is_read_only = 1 THEN 'read only' ELSE '' END AS [read only], CASE WHEN is_auto_shrink_on = 1 THEN 'autoshrink' ELSE '' END AS [autoshrink], CASE WHEN is_auto_create_stats_on = 1 THEN 'auto create statistics' ELSE '' END AS [auto create statistics], CASE WHEN is_auto_update_stats_on = 1 THEN 'auto update statistics' ELSE '' END AS [auto update statistics], CASE WHEN is_in_standby = 1 THEN 'standby' ELSE '' END AS [standby], CASE WHEN is_cleanly_shutdown = 1 THEN 'cleanly shutdown' ELSE '' END AS [cleanly shutdown] FROM sys.databases DB ORDER BY dbName, [Last backup] DESC, NAME Please let me know if you find this information useful. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, Readers Contribution, SQL, SQL Authority, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQLServer, T SQL, Technology

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• SQL SERVER – Activity Monitor and Performance Issue

  - by pinaldave

  We had wonderful SQLAuthority News – Community Tech Days – December 11, 2010 event yesterday. After the event, we had meeting among Jacob Sebastian, Vinod Kumar, Rushabh Mehta and myself. We all were sharing our experience about performance tuning consultations. During the conversation, Jacob has shared wonderful story of his recent observation. The story is very small but the moral of the story is very important. The story is about a client, who had continuously performance issues. Client used Activity Monitor (Read More: SQL SERVER – 2008 – Location of Activity Monitor – Where is SQL Serve Activity Monitor Located) to check the performance issues. The pattern of the performance issues was very much common all the time. Every time, after a while the computer stopped responding. After doing in-depth performance analysis, Jacob realized that client once opened activity monitor never closed it. The same activity monitor itself is very expensive process. The tool, which helped to debug the performance issues, also helped (negatively) to bring down the server. After closing the activity monitor which was open for long time, the server did not have performance issues. Moral of the story: Activity Monitor is great tool but use it with care and close it when not needed. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Best Practices, Pinal Dave, SQL, SQL Authority, SQL Optimization, SQL Performance, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• SQL SERVER – CTRL+SHIFT+] Shortcut to Select Code Between Two Parenthesis

  - by pinaldave

  Every weekend brings creative ideas and accidents brings best unknown secrets in front of us. Just a day while working with complex SQL Server code in SSMS I came across very interesting shortcut which I have never used before and instantly fell in love with it. It is totally possible that you are familiar with this but for me it was the first time and I was surprised that I did know know this short cut so far. Shortcut key is CTRL+SHIFT+]. This key can be very useful when dealing with multiple subqueries, CTE or query with multiple parentheses. When exercised this shortcut key it selects T-SQL code between two parentheses. Let us see the examples to understand the same. In each of the examples I have put the cursor at the position displayed and pressed CTRL+SHIFT+] and it has selected the code between two corresponding parentheses. Cursor position 1 Cursor position 2 Cursor position 3 If you are a developer and have to code with complex queries, you will totally appreciate that this feature can save so much of the time for development. I often remember my experience as a developer when I have lost a lot of hours to just balance parentheses. As I said yesterday I found this shortcut accidently. How many of you were aware of this feature? Is there any other useful feature you would like to share with us? Please leave a comment and if I have not covered it earlier, I will share it due credit on this blog. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Server Management Studio, SQL Tips and Tricks, T SQL, Technology Tagged: SQL Shortcut

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• SQL SERVER – Convert IN to EXISTS – Performance Talk

  - by pinaldave

  In recent training one of the attendee asked if I can show simple method to convert IN clause to EXISTS clause. Here is the simple example. USE AdventureWorks GO -- use of = SELECT * FROM HumanResources.Employee E WHERE E.EmployeeID = ( SELECT EA.EmployeeID FROM HumanResources.EmployeeAddress EA WHERE EA.EmployeeID = E.EmployeeID) GO -- use of exists SELECT * FROM HumanResources.Employee E WHERE EXISTS ( SELECT EA.EmployeeID FROM HumanResources.EmployeeAddress EA WHERE EA.EmployeeID = E.EmployeeID) GO It is NOT necessary that every time when IN is replaced by EXISTS it gives better performance. However, in our case listed above it does for sure give better performance. Click on below image to see the execution plan. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: SQL, SQL Authority, SQL Optimization, SQL Performance, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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