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  • SQL SERVER – Download Microsoft SQL Server Compact 4.0 SP1

    - by pinaldave
    Microsoft SQL Server Compact 4.0 is a free, embedded database that software developers can use for building ASP.NET websites and Windows desktop applications. SQL Server Compact 4.0 is the default database for Microsoft WebMatrix. For enhanced development and debugging capabilities, including designer support, Visual Studio can be used to develop ASP.NET web applications and websites using SQL Server Compact 4.0. Enabled to work in the medium or partial trust environments in the web servers, and can be easily deployed along with the website to the third party website hosting service providers. SQL Server CE 4.0 also provides stronger data security with the use of the SHA2 encryption algorithms for encrypting the databases. Latest version also supports T-SQL syntax enhancement by adding support for OFFSET and FETCH that can be used to write paging queries. Used with ADO.NET Entity Framework, SQL Server Compact now supports the columns that have server generated keys like identity, rowguid etc. and the code-first programming model. SQL Server Compact 4.0 is freely redistributable under a redistribution license agreement. SQL Server Compact 3.5 and SQL Server Compact 4.0 can be installed and work side by side on a desktop. Download Microsoft SQL Server Compact 4.0 SP1 Here are my earlier article on SQL Server CE Difference Between SQL Server Compact Edition (CE) and SQL Server Express Edition SQL SERVER – CE – 3 Links to Performance Tuning Compact Edition SQL SERVER – CE – List of Information_Schema System Tables SQL SERVER – Server Side Paging in SQL Server CE (Compact Edition) SQL SERVER – CE – Samples Database for SQL CE 4.0 Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Download, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • SQL SERVER – Get Latest SQL Query for Sessions – DMV

    - by pinaldave
    In recent SQL Training I was asked, how can one figure out what was the last SQL Statement executed in sessions. The query for this is very simple. It uses two DMVs and created following quick script for the same. SELECT session_id, TEXT FROM sys.dm_exec_connections CROSS APPLY sys.dm_exec_sql_text(most_recent_sql_handle) AS ST While working with DMVs if you ever find any DMV has column with name sql_handle you can right away join that DMV with another DMV sys.dm_exec_sql_text and can get the text of the SQL statement. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, SQL, SQL Authority, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology Tagged: DMV, SQL DMV

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  • SQL SERVER – ASYNC_IO_COMPLETION – Wait Type – Day 11 of 28

    - by pinaldave
    For any good system three things are vital: CPU, Memory and IO (disk). Among these three, IO is the most crucial factor of SQL Server. Looking at real-world cases, I do not see IT people upgrading CPU and Memory frequently. However, the disk is often upgraded for either improving the space, speed or throughput. Today we will look at another IO-related wait type. From Book On-Line: Occurs when a task is waiting for I/Os to finish. ASYNC_IO_COMPLETION Explanation: Any tasks are waiting for I/O to finish. If by any means your application that’s connected to SQL Server is processing the data very slowly, this type of wait can occur. Several long-running database operations like BACKUP, CREATE DATABASE, ALTER DATABASE or other operations can also create this wait type. Reducing ASYNC_IO_COMPLETION wait: When it is an issue related to IO, one should check for the following things associated to IO subsystem: Look at the programming and see if there is any application code which processes the data slowly (like inefficient loop, etc.). Note that it should be re-written to avoid this  wait type. Proper placing of the files is very important. We should check the file system for proper placement of the files – LDF and MDF on separate drive, TempDB on another separate drive, hot spot tables on separate filegroup (and on separate disk), etc. Check the File Statistics and see if there is a higher IO Read and IO Write Stall SQL SERVER – Get File Statistics Using fn_virtualfilestats. Check event log and error log for any errors or warnings related to IO. If you are using SAN (Storage Area Network), check the throughput of the SAN system as well as configuration of the HBA Queue Depth. In one of my recent projects, the SAN was performing really badly and so the SAN administrator did not accept it. After some investigations, he agreed to change the HBA Queue Depth on the development setup (test environment). As soon as we changed the HBA Queue Depth to quite a higher value, there was a sudden big improvement in the performance. It is very likely to happen that there are no proper indexes on the system and yet there are lots of table scans and heap scans. Creating proper index can reduce the IO bandwidth considerably. If SQL Server can use appropriate cover index instead of clustered index, it can effectively reduce lots of CPU, Memory and IO (considering cover index has lesser columns than cluster table and all other; it depends upon the situation). You can refer to the following two articles I wrote that talk about how to optimize indexes: Create Missing Indexes Drop Unused Indexes Checking Memory Related Perfmon Counters SQLServer: Memory Manager\Memory Grants Pending (Consistent higher value than 0-2) SQLServer: Memory Manager\Memory Grants Outstanding (Consistent higher value, Benchmark) SQLServer: Buffer Manager\Buffer Hit Cache Ratio (Higher is better, greater than 90% for usually smooth running system) SQLServer: Buffer Manager\Page Life Expectancy (Consistent lower value than 300 seconds) Memory: Available Mbytes (Information only) Memory: Page Faults/sec (Benchmark only) Memory: Pages/sec (Benchmark only) Checking Disk Related Perfmon Counters Average Disk sec/Read (Consistent higher value than 4-8 millisecond is not good) Average Disk sec/Write (Consistent higher value than 4-8 millisecond is not good) Average Disk Read/Write Queue Length (Consistent higher value than benchmark is not good) Read all the post in the Wait Types and Queue series. Note: The information presented here is from my experience and there is no way that I claim it to be accurate. I suggest reading Book OnLine for further clarification. All the discussions of Wait Stats in this blog are generic and vary from system to system. It is recommended that you test this on a development server before implementing it to a production server. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQL Wait Stats, SQL Wait Types, T SQL, Technology

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  • SQL SERVER – Checklist for Analyzing Slow-Running Queries

    - by pinaldave
    I am recently working on upgrading my class Microsoft SQL Server 2005/2008 Query Optimization and & Performance Tuning with additional details and more interesting examples. While working on slide deck I realized that I need to have one solid slide which talks about checklist for analyzing slow running queries. A quick search on my saved [...]

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  • SQL SERVER – FT_IFTS_SCHEDULER_IDLE_WAIT – Full Text – Wait Type – Day 13 of 28

    - by pinaldave
    In the last few days during this series, I got many question about this Wait type. It would be great if you read my original related wait stats query in the first post because I have filtered it out in WHERE clause. However, I still get questions about this being one of the most wait types they encounter. The truth is, this is a background task processing and it really does not matter and it should be filtered out. There are many new Wait types related to Full Text Search that are introduced in SQL Server 2008. If you run the following query, you will be able to find them in the list. Currently there is not enough information for all of them available on BOL or any other place. But don’t worry; I will write an in-depth article when I learn more about them. SELECT * FROM sys.dm_os_wait_stats WHERE wait_type LIKE 'FT_%' The result set will contain following rows. FT_RESTART_CRAWL FT_METADATA_MUTEX FT_IFTSHC_MUTEX FT_IFTSISM_MUTEX FT_IFTS_RWLOCK FT_COMPROWSET_RWLOCK FT_MASTER_MERGE FT_IFTS_SCHEDULER_IDLE_WAIT We have understood so far that there is not much information available. But the problem is when you have this Wait type, what should you do?  The answer is to filter them out for the moment (i.e, do not pay attention on them) and focus on other pressing issues in wait stats or performance tuning. Here are two of my informal suggestions, which are totally independent from wait stats: Turn off the Full Text Search service in your system if you are  not necessarily using it on your server. Learn proper Full Text Search methodology. You can get Michael Coles’ book: Pro Full-Text Search in SQL Server 2008. Now I invite you to speak out your suggestions or any input regarding Full Text-related best practices and wait stats issue. Please leave a comment. Note: The information presented here is from my experience and there is no way that I claim it to be accurate. I suggest reading Book OnLine for further clarification. All the discussions of Wait Stats in this blog are generic and vary from system to system. It is recommended that you test this on a development server before implementing it to a production server. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQL Wait Stats, SQL Wait Types, T SQL, Technology

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  • SQL SERVER – SQL Server Misconceptions and Resolution – A Practical Perspective – TechEd 2012 India

    - by pinaldave
    TechEd India 2012 is just around the corner and I will be presenting there in two different sessions. On the very first day of this event, my presentation will be all about SQL Server Misconceptions and Resolution – A Practical Perspective. The dictionary tells us that a “misconception” means a view or opinion that is incorrect and is based on faulty thinking or understanding. In SQL Server, there are so many misconceptions. In fact, when I hear some of these misconceptions, I feel like fainting at that very moment! Seriously, at one time, I came across the scenario where instead of using INSERT INTO…SELECT, the developer used CURSOR believing that cursor is faster (duh!). Here is the link the blog post related to this. Pinal and Vinod in 2009 I have been presenting in TechEd India for last three years. This is my fourth opportunity to present a technical session on SQL Server. Just like the previous years, I decided to present something different. Here is a novelty of this year: I will be presenting this session with Vinod Kumar. Vinod Kumar and I have a great synergy when we work together. So far, we have written one SQL Server Interview Questions and Answers book and 2 video courses: (1) SQL Server Questions and Answers (2) SQL Server Performance: Indexing Basics. Pinal and Vinod in 2011 When we sat together and started building an outline for this course, we had many options in mind for this tango session. However, we have decided that we will make this session as lively as possible while keeping it natural at the same time. We know our flow and we know our conversation highlight, but we do not know what exactly each of us is going to present. We have decided to challenge each other on stage and push each other’s knowledge to the verge. We promise that the session will be entertaining with lots of SQL Server trivia, tips and tricks. Here are the challenges that I’ll take on: I will puzzle Vinod with my difficult questions I will present such misconception that Vinod will have no resolution for it. I need your help.  Will you help me stump Vinod? If yes, come and attend our session and join me to prove that together we are superior (a friendly brain clash, but we must win!). SQL Server enthusiasts and SQL Server fans are going to have gala time at #TechEdIn as we have a very solid lineup of the speaker and extremely interesting sessions at TechEdIn. Read the complete blog post of Vinod. Session Details Title: SQL Server Misconceptions and Resolution – A Practical Perspective (Add to Calendar) Abstract: “Earth is flat”! – An ancient common misconception, which has been proven incorrect as we progressed in modern times. In this session we will see various database misconceptions prevailing and their resolution with the aid of the demos. In this unique session audience will be part of the conversation and resolution. Date and Time: March 21, 2012, 15:15 to 16:15 Location: Hotel Lalit Ashok - Kumara Krupa High Grounds, Bengaluru – 560001, Karnataka, India. Add to Calendar Please submit your questions in the comments area and I will be for sure discussing them during my session. If I pick your question to discuss during my session, here is your gift I commit right now – SQL Server Interview Questions and Answers Book. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Interview Questions and Answers, SQL Performance, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology Tagged: TechEd, TechEdIn

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  • SQL SERVER – IO_COMPLETION – Wait Type – Day 10 of 28

    - by pinaldave
    For any good system three things are vital: CPU, Memory and IO (disk). Among these three, IO is the most crucial factor of SQL Server. Looking at real-world cases, I do not see IT people upgrading CPU and Memory frequently. However, the disk is often upgraded for either improving the space, speed or throughput. Today we will look at an IO-related wait types. From Book On-Line: Occurs while waiting for I/O operations to complete. This wait type generally represents non-data page I/Os. Data page I/O completion waits appear as PAGEIOLATCH_* waits. IO_COMPLETION Explanation: Any tasks are waiting for I/O to finish. This is a good indication that IO needs to be looked over here. Reducing IO_COMPLETION wait: When it is an issue concerning the IO, one should look at the following things related to IO subsystem: Proper placing of the files is very important. We should check the file system for proper placement of files – LDF and MDF on a separate drive, TempDB on another separate drive, hot spot tables on separate filegroup (and on separate disk),etc. Check the File Statistics and see if there is higher IO Read and IO Write Stall SQL SERVER – Get File Statistics Using fn_virtualfilestats. Check event log and error log for any errors or warnings related to IO. If you are using SAN (Storage Area Network), check the throughput of the SAN system as well as the configuration of the HBA Queue Depth. In one of my recent projects, the SAN was performing really badly so the SAN administrator did not accept it. After some investigations, he agreed to change the HBA Queue Depth on development (test environment) set up and as soon as we changed the HBA Queue Depth to quite a higher value, there was a sudden big improvement in the performance. It is very possible that there are no proper indexes in the system and there are lots of table scans and heap scans. Creating proper index can reduce the IO bandwidth considerably. If SQL Server can use appropriate cover index instead of clustered index, it can effectively reduce lots of CPU, Memory and IO (considering cover index has lesser columns than cluster table and all other; it depends upon the situation). You can refer to the two articles that I wrote; they are about how to optimize indexes: Create Missing Indexes Drop Unused Indexes Checking Memory Related Perfmon Counters SQLServer: Memory Manager\Memory Grants Pending (Consistent higher value than 0-2) SQLServer: Memory Manager\Memory Grants Outstanding (Consistent higher value, Benchmark) SQLServer: Buffer Manager\Buffer Hit Cache Ratio (Higher is better, greater than 90% for usually smooth running system) SQLServer: Buffer Manager\Page Life Expectancy (Consistent lower value than 300 seconds) Memory: Available Mbytes (Information only) Memory: Page Faults/sec (Benchmark only) Memory: Pages/sec (Benchmark only) Checking Disk Related Perfmon Counters Average Disk sec/Read (Consistent higher value than 4-8 millisecond is not good) Average Disk sec/Write (Consistent higher value than 4-8 millisecond is not good) Average Disk Read/Write Queue Length (Consistent higher value than benchmark is not good) Note: The information presented here is from my experience and there is no way that I claim it to be accurate. I suggest reading Book OnLine for further clarification. All the discussions of Wait Stats in this blog are generic and vary from system to system. It is recommended that you test this on a development server before implementing it to a production server. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQL Wait Types, SQL White Papers, T SQL, Technology

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  • SQL SERVER – Cardinality Estimation and Performance – SQL in Sixty Seconds #072

    - by Pinal Dave
    Yesterday I wrote blog post based on my latest Pluralsight course on learning SQL Server 2014. I discussed newly introduced cardinality estimation in SQL Server 2014 and how it improves the performance of the query. The cardinality estimation logic is responsible for quality of query plans and majorly responsible for improving performance for any query. This logic was not updated for quite a while, but in the latest version of SQL Server 2104 this logic is re-designed. The new logic now incorporates various assumptions and algorithms of OLTP and warehousing workload. I hope my earlier blog post clearly explained how new cardinality estimation logic improves performance. If not, I suggest you watch following quick video where I explain this concept in extremely simple words. You can download the code used in this course from Simple Demo of New Cardinality Estimation Features of SQL Server 2014. Action Item Here are the blog posts I have previously written. You can read it over here: Simple Demo of New Cardinality Estimation Features of SQL Server 2014 Pluralsight Course You can subscribe to my YouTube Channel for frequent updates. Reference: Pinal Dave (http://blog.sqlauthority.com)Filed under: PostADay, SQL, SQL Authority, SQL Performance, SQL Query, SQL Server, SQL Server Management Studio, SQL Tips and Tricks, T SQL, Video

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  • SQLAuthority News – Online Webcast How to Identify Resource Bottlenecks – Wait Types and Queues

    - by pinaldave
    As all of you know I have been working a recently on the subject SQL Server Wait Statistics, the reason is since I have published book on this subject SQL Wait Stats Joes 2 Pros: SQL Performance Tuning Techniques Using Wait Statistics, Types & Queues [Amazon] | [Flipkart] | [Kindle], lots of question and answers I am encountering. When I was writing the book, I kept version 1 of the book in front of me. I wanted to write something which one can use right away. I wanted to create an primer for everybody who have not explored wait stats method of performance tuning. Well, the books have been very well received and in fact we ran out of huge stock 2 times in India so far and once in USA during SQLPASS. I have received so many questions on this subject that I feel I can write one more book of the same size. I have been asked if I can create videos which can go along with this book. Personally I am working with SQL Server 2012 CTP3 and there are so many new wait types, I feel the subject of wait stats is going to be very very crucial in next version of SQL Server. If you have not started learning about this subject, I suggest you at least start exploring this right now. Learn how to begin on this subject atleast as when the next version comes in, you know how to read DMVs. I will be presenting on the same subject of performance tuning by wait stats in webcast embarcadero SQL Server Community Webinar. Here are few topics which we will be covering during the webinar. Beginning with SQL Wait Stats Understanding various aspect of SQL Wait Stats Understanding Query Life Cycle Identifying three TOP wait Stats Resolution of the common 3 wait types and queues Details of the webcast: How to Identify Resource Bottlenecks – Wait Types and Queues Date and Time: Wednesday, November 2, 11:00 AM PDT Registration Link I thank embarcadero for organizing opportunity for me to share my experience on subject of wait stats and connecting me with community to further take this subject to next level. One more interesting thing, I will ask one question at the end of the webinar and I will be giving away 5 copy of my SQL Wait Stats print book to first five correct answers. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: About Me, Pinal Dave, PostADay, 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 – Puzzle – Challenge – Error While Converting Money to Decimal

    - by pinaldave
    Earlier I wrote SQL SERVER – Challenge – Puzzle – Usage of FAST Hint and I did receive some good comments. Here is another question to tease your mind. Run following script and you will see that it will thrown an error. DECLARE @mymoney MONEY; SET @mymoney = 12345.67; SELECT CAST(@mymoney AS DECIMAL(5,2)) MoneyInt; GO The datatype of money is also visually look similar to the decimal, why it would throw following error: Msg 8115, Level 16, State 8, Line 3 Arithmetic overflow error converting money to data type numeric. Please leave a comment with explanation and I will post a your answer on this blog with due credit. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Pinal Dave, SQL, SQL Authority, SQL Error Messages, SQL Puzzle, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQLServer, T SQL, Technology

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  • SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Complete Downloadable List – Day 0 of 31

    - by pinaldave
    This blog post is running list of the blog posts in the series of Interview Questions and Answers. At the end of the 31st day of the month, a FREE PDF will be posted here which can be downloadable for offline review. Please scroll below to see latest post for the day. SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Introduction – Day 1 of 31 In this very first blog post – various aspect of the interview questions and answers are discussed. Some people like the subject for their helpful hints and thought provoking subject, and others dislike these posts because they feel it is nothing more than cheating.  I’d like to discuss the pros and cons of a Question and Answer format here. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Documentation, SQL Download, SQL Interview Questions and Answers, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • SQL SERVER – Fix : Error : 3117 : The log or differential backup cannot be restored because no files

    - by pinaldave
    I received the following email from one of my readers. Dear Pinal, I am new to SQL Server and our regular DBA is on vacation. Our production database had some problem and I have just restored full database backup to production server. When I try to apply log back I am getting following error. I am sure, this is valid log backup file. Screenshot is attached. [Few other details regarding server/ip address removed] Msg 3117, Level 16, State 1, Line 1 The log or differential backup cannot be restored because no files are ready to roll forward. Msg 3013, Level 16, State 1, Line 1 RESTORE LOG is terminating abnormally. Screenshot attached. [Removed as it contained live IP address] Please help immediately. Well I have answered this question in my earlier post, 2 years ago, over here SQL SERVER – Fix : Error : Msg 3117, Level 16, State 4 The log or differential backup cannot be restored because no files are ready to rollforward. However, I will try to explain it a little more this time. For SQL Server database to be used it should in online state. There are multiple states of SQL Server Database. ONLINE (Available – online for data) OFFLINE RESTORING RECOVERING RECOVERY PENDING SUSPECT EMERGENCY (Limited Availability) If the database is online, it means it is active and in operational mode. It will not make sense to apply further log from backup if the operations have continued on this database. The common practice during the backup restore process is to specify the keyword RECOVERY when the database is restored. When RECOVERY keyword is specified, the SQL Server brings back the database online and will not accept any further log backups. However, if you want to restore more than one backup files, i.e. after restoring the full back up if you want to apply further differential or log backup you cannot do that when database is online and already active. You need to have your database in the state where it can further accept the backup data and not the online data request. If the SQL Server is online and also accepts database backup file, then there can be data inconsistency. This is the reason that when there are more than one database backup files to be restored, one has to restore the database with NO RECOVERY keyword in the RESTORE operation. I suggest you all to read one more post written by me earlier. In this post, I explained the time line with image and graphic SQL SERVER – Backup Timeline and Understanding of Database Restore Process in Full Recovery Model. Sample Code for reference: RESTORE DATABASE AdventureWorks FROM DISK = 'C:\AdventureWorksFull.bak' WITH NORECOVERY; RESTORE DATABASE AdventureWorks FROM DISK = 'C:\AdventureWorksDiff.bak' WITH RECOVERY; In this post, I am not trying to cover complete backup and recovery. I am just attempting to address one type of error and its resolution. Please test these scenarios on the development server. Playing with live database backup and recovery is always very crucial and needs to be properly planned. Leave a comment here if you need help with this subject. Similar Post: SQL SERVER – Restore Sequence and Understanding NORECOVERY and RECOVERY Note: We will cover Standby Server maintenance and Recovery in another blog post and it is intentionally, not covered this post. Reference : Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, Readers Question, SQL, SQL Authority, SQL Backup and Restore, SQL Error Messages, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • SQLAuthority News – SQL Server Cheat Sheet from MidnightDBA

    - by pinaldave
    When I read the article from MidnightDBA (I should say MidnightDBAs because it is about Jen and Sean) regarding T-SQL for the Absentminded DBA, my natural reaction was that it is a perfect extension. A year ago around the same month, I had created SQL Server Cheatsheet. I have distributed a lot of copies of it since I produced it. In fact, while attending TechMela in Nepal today, I am getting many requests to get copies of SQL Server Cheatsheet. When I checked my RSS feed, I realized that Jen and Sean have a perfect cheat sheet for intermediate level developers. I would like to suggest to all of you to read their post and download the Absentminded DBA’s Cheat Sheet for IntermediateTSQL. It is available in two formats: PDF and Docx. I just love how the members of the community help each other grow. I am fortunate that I have received excellent feedback/corrections and criticism on my blog posts for so many times. Criticism and corrections, after all, are absolutely needed and make a better community as a whole. Reference : Pinal Dave (http://blog.SQLAuthority.com) Filed under: MVP, Pinal Dave, SQL, SQL Authority, SQL Download, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQLAuthority News, T SQL, Technology Tagged: SQL Cheat Sheet

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  • SQL SERVER – WRITELOG – Wait Type – Day 17 of 28

    - by pinaldave
    WRITELOG is one of the most interesting wait types. So far we have seen a lot of different wait types, but this log type is associated with log file which makes it interesting to deal with. From Book On-Line: WRITELOG Occurs while waiting for a log flush to complete. Common operations that cause log flushes are checkpoints and transaction commits. WRITELOG Explanation: This wait type is usually seen in the heavy transactional database. When data is modified, it is written both on the log cache and buffer cache. This wait type occurs when data in the log cache is flushing to the disk. During this time, the session has to wait due to WRITELOG. I have recently seen this wait type’s persistence at my client’s place, where one of the long-running transactions was stopped by the user causing it to roll back. In the future, I will see if I could re-create this situation once again on my machine to validate the relation. Reducing WRITELOG wait: There are several suggestions to reduce this wait stats: Move Transaction Log to Separate Disk from mdf and other files. Avoid cursor-like coding methodology and frequent committing of statements. Find the most active file based on IO stall time based on the script written over here. You can also use fn_virtualfilestats to find IO-related issues using the script mentioned over here. Check the IO-related counters (PhysicalDisk:Avg.Disk Queue Length, PhysicalDisk:Disk Read Bytes/sec and PhysicalDisk :Disk Write Bytes/sec) for additional details. Read about them over here. There are two excellent resources by Paul Randal, I suggest you understand the subject from those videos. The links to videos are here and here. Note: The information presented here is from my experience and there is no way that I claim it to be accurate. I suggest reading Book OnLine for further clarification. All the discussion of Wait Stats in this blog is generic and varies from system to system. It is recommended that you test this on a development server before implementing it to a production server. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQL Wait Stats, SQL Wait Types, T SQL, Technology

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  • SQL SERVER – PAGEIOLATCH_DT, PAGEIOLATCH_EX, PAGEIOLATCH_KP, PAGEIOLATCH_SH, PAGEIOLATCH_UP – Wait Type – Day 9 of 28

    - by pinaldave
    It is very easy to say that you replace your hardware as that is not up to the mark. In reality, it is very difficult to implement. It is really hard to convince an infrastructure team to change any hardware because they are not performing at their best. I had a nightmare related to this issue in a deal with an infrastructure team as I suggested that they replace their faulty hardware. This is because they were initially not accepting the fact that it is the fault of their hardware. But it is really easy to say “Trust me, I am correct”, while it is equally important that you put some logical reasoning along with this statement. PAGEIOLATCH_XX is such a kind of those wait stats that we would directly like to blame on the underlying subsystem. Of course, most of the time, it is correct – the underlying subsystem is usually the problem. From Book On-Line: PAGEIOLATCH_DT Occurs when a task is waiting on a latch for a buffer that is in an I/O request. The latch request is in Destroy mode. Long waits may indicate problems with the disk subsystem. PAGEIOLATCH_EX Occurs when a task is waiting on a latch for a buffer that is in an I/O request. The latch request is in Exclusive mode. Long waits may indicate problems with the disk subsystem. PAGEIOLATCH_KP Occurs when a task is waiting on a latch for a buffer that is in an I/O request. The latch request is in Keep mode. Long waits may indicate problems with the disk subsystem. PAGEIOLATCH_SH Occurs when a task is waiting on a latch for a buffer that is in an I/O request. The latch request is in Shared mode. Long waits may indicate problems with the disk subsystem. PAGEIOLATCH_UP Occurs when a task is waiting on a latch for a buffer that is in an I/O request. The latch request is in Update mode. Long waits may indicate problems with the disk subsystem. PAGEIOLATCH_XX Explanation: Simply put, this particular wait type occurs when any of the tasks is waiting for data from the disk to move to the buffer cache. ReducingPAGEIOLATCH_XX wait: Just like any other wait type, this is again a very challenging and interesting subject to resolve. Here are a few things you can experiment on: Improve your IO subsystem speed (read the first paragraph of this article, if you have not read it, I repeat that it is easy to say a step like this than to actually implement or do it). This type of wait stats can also happen due to memory pressure or any other memory issues. Putting aside the issue of a faulty IO subsystem, this wait type warrants proper analysis of the memory counters. If due to any reasons, the memory is not optimal and unable to receive the IO data. This situation can create this kind of wait type. Proper placing of files is very important. We should check file system for the proper placement of files – LDF and MDF on separate drive, TempDB on separate drive, hot spot tables on separate filegroup (and on separate disk), etc. Check the File Statistics and see if there is higher IO Read and IO Write Stall SQL SERVER – Get File Statistics Using fn_virtualfilestats. It is very possible that there are no proper indexes on the system and there are lots of table scans and heap scans. Creating proper index can reduce the IO bandwidth considerably. If SQL Server can use appropriate cover index instead of clustered index, it can significantly reduce lots of CPU, Memory and IO (considering cover index has much lesser columns than cluster table and all other it depends conditions). You can refer to the two articles’ links below previously written by me that talk about how to optimize indexes. Create Missing Indexes Drop Unused Indexes Updating statistics can help the Query Optimizer to render optimal plan, which can only be either directly or indirectly. I have seen that updating statistics with full scan (again, if your database is huge and you cannot do this – never mind!) can provide optimal information to SQL Server optimizer leading to efficient plan. Checking Memory Related Perfmon Counters SQLServer: Memory Manager\Memory Grants Pending (Consistent higher value than 0-2) SQLServer: Memory Manager\Memory Grants Outstanding (Consistent higher value, Benchmark) SQLServer: Buffer Manager\Buffer Hit Cache Ratio (Higher is better, greater than 90% for usually smooth running system) SQLServer: Buffer Manager\Page Life Expectancy (Consistent lower value than 300 seconds) Memory: Available Mbytes (Information only) Memory: Page Faults/sec (Benchmark only) Memory: Pages/sec (Benchmark only) Checking Disk Related Perfmon Counters Average Disk sec/Read (Consistent higher value than 4-8 millisecond is not good) Average Disk sec/Write (Consistent higher value than 4-8 millisecond is not good) Average Disk Read/Write Queue Length (Consistent higher value than benchmark is not good) Note: The information presented here is from my experience and there is no way that I claim it to be accurate. I suggest reading Book OnLine for further clarification. All of the discussions of Wait Stats in this blog is generic and varies from system to system. It is recommended that you test this on a development server before implementing it to a production server. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQL Wait Stats, SQL Wait Types, T SQL, Technology

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  • SQLAuthority News – 2 Security Updates for SQL Server 2000 SP 4 Users

    - by pinaldave
    If you are using SQL Server 2000 still today my very first recommendation to you is to upgrade to SQL Server 2012. SQL Server 2000 is now 12 years old product and since then many new enhancements as well features which are relevant to current growth and progress in Informational Industry. Now is the time to catch up with the latest trends. Here is one more point for you to notice if this helps you consider to upgrade to the latest version. One can’t upgrade directly from SQL Server 2000 to SQL Server 2012. You need to first upgrade to either SQL Server 2005/2008/R2 and then further plan to upgrade to SQL Server 2012. There is no direct upgrade path for SQL Server 2000 to SQL Server 2012. I strongly believe this is the time to upgrade to the latest version. Well, also there is a rule that to let something continue if it is not broken and working fine. If you are following that rule and still using SQL Server 2000 I strongly suggest that you upgrade your SQL Server 2000 SP4 and update it with latest Security updates. Here are two important SQL Server Security Updates. Security Update for SQL Server 2000 Service Pack 4 (KB983811) Security Update for SQL Server 2000 Service Pack 4 (KB983812) As we are talking about SQL Server 2000 let me ask you a quick question – how many of you are still using SQL Server 2000 or earlier version in a production system on at least one server? Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Download, SQL Query, SQL Security, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • SQL SERVER – Question to You – When to use Function and When to use Stored Procedure

    - by pinaldave
    This week has been very interesting week. I have asked few questions to users and have received remarkable participation on the subject. Q1) SQL SERVER – Puzzle – SELECT * vs SELECT COUNT(*) Q2) SQL SERVER – Puzzle – Statistics are not Updated but are Created Once Keeping the same spirit up, I am asking the third question over here. Q3) When to use User Defined Function and when to use Stored Procedure in your development? Personally, I believe that they are both different things - they cannot be compared. I can say, it will be like comparing apples and oranges. Each has its own unique use. However, they can be used interchangeably at many times and in real life (i.e., production environment). I have personally seen both of these being used interchangeably many times. This is the precise reason for asking this question. When do you use Function and when do you use Stored Procedure? What are Pros and Cons of each of them when used instead of each other? If you are going to answer that ‘To avoid repeating code, you use Function’ - please think harder! Stored procedure can do the same. In SQL Server Denali, even the stored procedure can return the result just like Function in SELECT statement; so if you are going to answer with ‘Function can be used in SELECT, whereas Stored Procedure cannot be used’ - again think harder! (link). Now, what do you say? I will post the answers of all the three questions with due credit next week. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, Readers Question, SQL, SQL Authority, SQL Function, SQL Puzzle, SQL Query, SQL Server, SQL Stored Procedure, SQL Tips and Tricks, SQLServer, T SQL, Technology

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  • SQL SERVER – Cleaning Up SQL Server Indexes – Defragmentation, Fillfactor – Video

    - by pinaldave
    Storing data non-contiguously on disk is known as fragmentation. Before learning to eliminate fragmentation, you should have a clear understanding of the types of fragmentation. When records are stored non-contiguously inside the page, then it is called internal fragmentation. When on disk, the physical storage of pages and extents is not contiguous. We can get both types of fragmentation using the DMV: sys.dm_db_index_physical_stats. Here is the generic advice for reducing the fragmentation. If avg_fragmentation_in_percent > 5% and < 30%, then use ALTER INDEX REORGANIZE: This statement is replacement for DBCC INDEXDEFRAG to reorder the leaf level pages of the index in a logical order. As this is an online operation, the index is available while the statement is running. If avg_fragmentation_in_percent > 30%, then use ALTER INDEX REBUILD: This is replacement for DBCC DBREINDEX to rebuild the index online or offline. In such case, we can also use the drop and re-create index method.(Ref: MSDN) Here is quick video which covers many of the above mentioned topics. While Vinod and I were planning about Indexing course, we had plenty of fun and learning. We often recording few of our statement and just left it aside. Afterwords we thought it will be really funny Here is funny video shot by Vinod and Myself on the same subject: Here is the link to the SQL Server Performance:  Indexing Basics. Here is the additional reading material on the same subject: SQL SERVER – Fragmentation – Detect Fragmentation and Eliminate Fragmentation SQL SERVER – 2005 – Display Fragmentation Information of Data and Indexes of Database Table SQL SERVER – De-fragmentation of Database at Operating System to Improve Performance Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Index, SQL Performance, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology, Video

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  • SQL SERVER – LOGBUFFER – Wait Type – Day 18 of 28

    - by pinaldave
    At first, I was not planning to write about this wait type. The reason was simple- I have faced this only once in my lifetime so far maybe because it is one of the top 5 wait types. I am not sure if it is a common wait type or not, but in the samples I had it really looks rare to me. From Book On-Line: LOGBUFFER Occurs when a task is waiting for space in the log buffer to store a log record. Consistently high values may indicate that the log devices cannot keep up with the amount of log being generated by the server. LOGBUFFER Explanation: The book online definition of the LOGBUFFER seems to be very accurate. On the system where I faced this wait type, the log file (LDF) was put on the local disk, and the data files (MDF, NDF) were put on SanDrives. My client then was not familiar about how the file distribution was supposed to be. Once we moved the LDF to a faster drive, this wait type disappeared. Reducing LOGBUFFER wait: There are several suggestions to reduce this wait stats: Move Transaction Log to Separate Disk from mdf and other files. (Make sure your drive where your LDF is has no IO bottleneck issues). Avoid cursor-like coding methodology and frequent commit statements. Find the most-active file based on IO stall time, as shown in the script written over here. You can also use fn_virtualfilestats to find IO-related issues using the script mentioned over here. Check the IO-related counters (PhysicalDisk:Avg.Disk Queue Length, PhysicalDisk:Disk Read Bytes/sec and PhysicalDisk :Disk Write Bytes/sec) for additional details. Read about them over here. If you have noticed, my suggestions for reducing the LOGBUFFER is very similar to WRITELOG. Although the procedures on reducing them are alike, I am not suggesting that LOGBUFFER and WRITELOG are same wait types. From the definition of the two, you will find their difference. However, they are both related to LOG and both of them can severely degrade the performance. Note: The information presented here is from my experience and there is no way that I claim it to be accurate. I suggest reading Book OnLine for further clarification. All the discussion of Wait Stats in this blog is generic and varies from system to system. It is recommended that you test this on a development server before implementing it to a production server. Reference: Pinal Dave (http://blog.SQLAuthority.com)   Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQL Wait Stats, SQL Wait Types, T SQL, Technology

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  • SQL SERVER – Download SQL Server Product Documentation

    - by pinaldave
    Today I just returned from Bangalore User Group Meeting. Attending User Group meeting is indeed fun and really great experience. The best part of the User Group is meeting like minded people and have a great conversation with them. During the meeting I was asked why one has to go online to access SQL Server Product Documentation. I can clearly see there can be many reasons for why one wants the documentation to be available offline. The reasons can be anything but not limited to Company Firewall No Internet (power failure, on road or disaster) Internet Bandwidth Limitatoin Company Proxy Issues … and much more… In this kind of situation one needs documentation which is offline and easily available in local computer. The Microsoft SQL Server 2012 setup installs only the Help Viewer and related components for managing Help settings. Setup does not directly install any documentation. All of the SQL Server documentation is available online. Well, Microsoft has recently released Production Documentation available for offline users as well. You just have to download the executable file and follow all the instructions. Please follow the link below for download of the file. There is detailed instruction on how to download and install the documentation offline. Product Documentation for Microsoft SQL Server 2012 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 – DVM sys.dm_os_sys_info Column Name Changed in SQL Server 2012

    - by pinaldave
    Have you ever faced situation where something does not work and when you try to go and fix it – you like fixing it and started to appreciate the breaking changes. Well, this is exactly I felt yesterday. Before I begin my story of yesterday I want to state it candidly that I do not encourage anybody to use * in the SELECT statement. One of the my DBA friend who always used my performance tuning script yesterday sent me email asking following question - “Every time I want to retrieve OS related information in SQL Server – I used DMV sys.dm_os_sys_info. I just upgraded my SQL Server edition from 2008 R2 to SQL Server 2012 RC0 and it suddenly stopped working. Well, this is not the production server so the issue is not big yet but eventually I need to resolve this error. Any suggestion?” The funny thing was original email was very long but it did not talk about what is the exact error beside the query is not working. I think this is the disadvantage of being too friendly on email sometime. Well, never the less, I quickly looked at the DMV on my SQL Server 2008 R2 and SQL Server 2012 RC0 version. To my surprise I found out that there were few columns which are renamed in SQL Server 2012 RC0. Usually when people see breaking changes they do not like it but when I see these changes I was happy as new names were meaningful and additionally their new conversion is much more practical and useful. Here are the columns previous names - Previous Column Name New Column Name physical_memory_in_bytes physical_memory_kb bpool_commit_target committed_target_kb bpool_visible visible_target_kb virtual_memory_in_bytes virtual_memory_kb bpool_commited committed_kb If you read it carefully you will notice that new columns now display few results in the KB whereas earlier result was in bytes. When I see the results in bytes I always get confused as I could not guess what exactly it will convert to. I like to see results in kb and I am glad that new columns are now displaying the results in the kb. I sent the details of the new columns to my friend and ask him to check the columns used in application. From my comment he quickly realized why he was facing error and fixed it immediately. Overall – all was well at the end and I learned something new. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL DMV, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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