Listing 3. However, when looking at the execution plan Figure 1 we can see that SQL Server still performs index scans against each of the five underlying tables. You may ask the obvious question why the range lock is required The reason is the way how SQL Server handles modifications of the data. The data is always. Microsoft SQL Server is a relational database management system developed by Microsoft. As a database server, it is a software product with the primary function of. Sql server interview questions and answers for freshers and experienced, SQL Server interview questions pdf, SQL Server online test, SQL server Jobs. This seems to be an area with quite a few myths and conflicting views. So what is the difference between a table variable and a local temporary table in SQL ServerAbout Sql Server Database design and development with Microsoft Sql Server. We, SQL Server professionals, like Enterprise Edition. It has many bells and whistles that make our life easier and less stressful. We wish to have Enterprise Edition installed on every server. Unfortunately, customers do not always share our opinions they want to save money. Using Hints. You can use comments in a SQL statement to pass instructions, or hints, to the Oracle Database optimizer. The optimizer uses these hints to choose an. Thats all there is to it. Once this has been created you can use this against any table and any database on your server. Next Steps. Add this to your scripts toolbox. SQL Tuning Overview. This chapter discusses goals for tuning, how to identify highresource SQL statements, explains what should be collected, and provides tuning. Maintenance-Plan-Generate-TSQL-600x387.png' alt='Sql Server Update Statistics Full Scan All Tables In A Database' title='Sql Server Update Statistics Full Scan All Tables In A Database' />More often than not, they choose to go with the Standard Edition, which is significantly less expensive. From performance standpoint, Standard Edition would suffice in many cases. Even though it lacks several nice features, it would work just fine even in large and busy systems. I dealt with many multi TB installations that handled thousands transactions per second using Standard Edition of SQL Server. Nevertheless, Standard edition lacks many of availability features offered in Enterprise Edition. Most important is index management. You cannot rebuild indexes keeping the table online. There are some tricks that can help reducing index rebuild time however, it would not help much with the large tables. This limitation has another interesting implication. In Standard Edition you cannot rebuild the indexes moving data to another filegroup transparently to the users. One of the cases when such an ability is very important is changing the database disk layout when you are upgrading disk subsystem. Obviously, it is very easy to do offline this is just the matter of copying database files. However, even with the fast disk subsystem, that can take hours in multi TB databases, which could violate your availability SLA. This is especially critical with the Cloud installations where IO subsystem is usually the biggest bottleneck due to the bad IO performance. The situation, however, is starting to change. Both, Microsoft Azure and Amazon AWS now offer fast SSD based IO solutions for very reasonable price. Unfortunately, the old installations were usually deployed to the old and slow disks and upgrading to the new drives will often lead to the hours of the downtime. Sql Server Performance Tuning Interview Questions Performance Tuning SQL Server Part 1. Q. What are the bottlenecks that effects the performance of a Database. Fortunately, you can move data to the different disk arrays almost transparently to the users even in non Enterprise Editions of SQL Servers. There are two ways how to accomplish it. The first one is very simple and can be done if system uses database mirroring. It requires failovers and secondary server downtime, which could lead to the data loss in case of disaster. The second approach works without the mirroring. It is slow, it generates large amount of transaction log records, it introduces huge index fragmentation however, it keeps database online most of the time. There is still the downtime involved although, it could be limited to just a few minutes. It will work in any SQL Server version and edition well, to be frank, I have not tried it in SQL Server 2. Lets look at both of those approaches in details. Moving database files with mirroring Involved. Database mirroring and, as matter of fact, Always On Availability Groups rely on the stream of transaction log records. Secondary servers apply the changes in the data files using file and page IDs as the reference. With exception of database file related operations, for example file creation, primary and secondary servers do not need to store database files in the same location it is possible to use different disk and folder structure on the servers. You can rely on this behavior if you need to move database files to the different drives. You can run ALTER DATABASE MODIFY FILEFILENAME. Everything will continue run normally those changes would not take place until the next database restart. Unfortunately, you cannot take database that participate in the mirroring session offline and you need to shut down entire instance of SQL Server. After that, you can physically move database files to the new location. On the primary server, the database mirroring will switch to the DISCONNECTED state. The database will continue to be available to the clients however, it remains unprotected all changes will be lost in case of disaster. You need to remember that file copy operation can take hours and you need to evaluate if you can take such a risk. It is also worth to mention that transaction log on the primary would not truncate and continue to grow even after log backups SQL Server needs to retain the log records until they sent to the secondary server. After the file copy operation is completed, you can start the instance the primary database will switch to SYNCHRONIZING state and wait until all log records have been transmitted to the secondary SYNCHRONIZED state. Then, you can failover and wash, rinse and repeat the process on the former primary server. To summarize, this process is very simple and transparent to the client applications. It is the good choice as long as you can afford the instance downtime and possibility of  data loss in case of disaster. If this is not the case, you will have to use much more complicated approach. When mirroring is not an option. We need to create the new data files in the secondary filegroups and shrink existing files by using DBCC SHRINKFILEEMPTYFILE command. This will move data from old to the new data files. Next, we need to repeat the same process with the primary filegroup. You cannot remove primary MDF file from the database although, you can make it very small and move all data from there. Next, we need to shrink the transaction log. Finally, we need to copy MDF and LDF files to the new location. This is offline operation however, both, MDF and LDF data files are small at this point and downtime is minimal. Lets look at the process in details. As the first step, lets create the test database with two filegroups and populate it with some data. For the demo purposes, I am assuming that C Old. Drive folder represents old and C New. Drive new disk arrays respectively. Data. Movement. Demo. NData. Movement. Demo, filename NC Old. DriveData. Movement. Demo. mdf, size 1. MB, filegrowth 5. MB. filegroup Secondary. NData. Movement. DemoSecondary. NC Old. DriveData. Movement. DemoSecondary. MB, filegrowth 5. MB. name NData. Movement. DemoSecondary. NC Old. DriveData. Movement. DemoSecondary. MB, filegrowth 5. MB. name NData. Movement. Demolog, filename NC Old. DriveData. Movement. Demolog. ldf, size 5. MB, filegrowth 5. MB. alter database Data. Movement. Demo set recovery full. Data. Movement. Demo. Data. On. Primary. ID int not null. Placeholder char8. PKData. On. Primary. ID. on Primary. Data. On. Secondary. ID int not null. Placeholder char8. PKData. On. Secondary. ID. on Secondary. N1C as select 0 union all select 0 2 rows. N2C as select 0 from N1 as T1 cross join N1 as T2 4 rows. N3C as select 0 from N2 as T1 cross join N2 as T2 1. N4C as select 0 from N3 as T1 cross join N3 as T2 2. N5C as select 0 from N4 as T1 cross join N4 as T2 6. NumsNum as select rownumber over order by select null from N5. Data. On. PrimaryID. Num from Nums. insert into dbo. Data. On. SecondaryID. ID from dbo. Data. On. Primary We can check the size of the data and log files along with their free space with the code below. File. Name. ,fg. File. Group. ,f. Path. ,f. Current. Size. MB. Space. Used. Used. Space. MB. Space. Used. Free. Space. Mb. Figure 1 shows the output of the statement. Database file stats after database creation. Moving data files from secondary filegroups. As the first step, you need to create new data files on the target drive. You can keep the same number of files as before, or use this as the opportunity to change the filegroup layout. In general, the number of files in the fielgroup greatly depends on the volatility of the data. Every data file has its own set of allocation map pages, which reduces the contention during page and extent allocations. Very large tables in SQL Server. Agreeing with Marc and Unkown above. You shouldnt have more than 3 or 4, if that, I would say 1 or maybe 2. You may know that the clustered index is the actual table on the disk so when a record is inserted, the database engine must sort it and place it in its sorted organized place on the disk. Non clustered indexes are not, they are supporting lookup tables. My VLDBs are laid out on the disk CLUSTERED INDEX according to the 1st point below. Reduce your clustered index to 1 or 2. The best field choices are the IDENTITY INT, if you have one, or a date field in which the fields are being added to the database, or some other field that is a natural sort of how your data is being added to the database. The point is you are trying to keep that data at the bottom of the table. This makes it so that there is no reorganzing going on or that its taking one and only one hit to get the data in the right place for the best read. Be sure to put the removed fields into non clustered indexes so you dont lose the lookup efficacy. I have NEVER put more than 4 fields on my VLDBs. If you have fields that are being update frequently and they are included in your clustered index, OUCH, thats going to reorganize the record on the disk and cause COSTLY fragmentation. Acoustic Fields And Waves In Solids Pdf Converter more. Check the fillfactor on your indexes. The larger the fill factor number 1. In relation to how many records you have and how many records your are inserting you will change the fillfactor or of your non clustered indexes to allow for the fill space when a record is inserted. If you change your clustered index to a sequential data field, then this wont matter as much on a clustered index. Rule of thumb IMO, 6. By dropping your fillfactor to 7. Eats up more space, but it sure beats having to DEFRAG every night see 4 belowMake sure the statistics exist on the table. If you want to sweep the database to create statistics using the spcreatestats indexonly, then SQL Server will create all the statistics on all the indexes that the engine has accumulated as requiring statistics. Dont leave off the indexonly attribute though or youll add statistics for every field, that would then not be good. Check the tableindexes using DBCC SHOWCONTIG to see which indexes are getting fragmented the most. I wont go into the details here, just know that you need to do it. Then based on that information, change the fillfactor up or down in relation to the changes the indexes are experiencing change and how fast over time. Setup a job schedule that will do online DBCC INDEXDEFRAG or offline DBCC DBREINDEX on individual indexes to defrag them. Warning dont do DBCC DBREINDEX on this large of a table without it being during maintenance time cause it will bring the apps down. CLUSTERED INDEX. Youve been warned. Test and test this part. Use the execution plans to see what SCANS, and FAT PIPES exist and adjust the indexes, then defrag and rewrite stored procs to get rid of those hot spots. If you see a RED object in your execution plan, its because there are not statistics on that field. Thats bad. This step is more of the art than the science. On off peak times, run the UPDATE STATISTICS WITH FULLSCAN to give the query engine as much information about the data distributions as you can. Otherwise do the standard UPDATE STATISTICS with standard 1. Sorry this is so long, but its extremely important. Ive only give you here minimal information but will help a ton. Theres some gut feelings and observations that go in to strategies used by these points that will require your time and testing. No need to go to Enterprise edition. I did though in order to get the features spoken of earlier with partitioning. But I did ESPECIALLY to have much better mult threading capabilities with searching and online DEFRAGING and maintenance. In Enterprise edition, it is much much better and more friendly with VLDBs. Standard edition doesnt handle doing DBCC INDEXDEFRAG with online databases as well.