SQL Performance Tuning Interview Questions

  • While this is kind of a softball question – if you know anything about SQL Server you should at least know the basic configuration options – it’s an important one to nail in the interview. Basically, when SQL Server is enabled the server instant listens to the TCSQL Server Performance Tuning.
  • SQL Server Performance Tuning and health check is a very challenging subject that requires expertise in Database Administration and Database Development. Here are few pointers how one can keep their SQL Server Performance Optimal. I am often asked what can one do keep SQL Server Health Optimal and SQL Server keep on running very smooth.
  • Here is the quick list of the pointers which one should consider for performance tuning.
  • Server/Instance Level Configuration Check.Review all the SQL Server/Instance Level settings of the server and tune it based on system workload.
  • I/O distribution is Analyze the I/O of your system and decide the best distribution for the I/O load. Perform object level analysis and do performance tuning at table level. Reduce I/O performance. bottlenecks and suggest optimal setting for read and write database. This is especially critical for databases that need to sustain heavy updates during peak usage hours.
  • SQL Server Resource Wait Stats Analysis.Wait Stat Analysis is very crucial for optimizing databases, but is often overlooked due to lack of understanding. Perform advanced resource wait statistics analysis to proactively reduce performance bottleneck.
  • Index Analysis.Indexes are considered valuable for performance improvements. Analyze all your indexes to identify non-performing indexes and missing indexes that can improve performance.
  • TempDB Space Review.Review the size and usage of your TempDB database.Database Files (MDF, NDF) and Log File Inspection.
  • Review all the files and filegroups of each of your databases and analysis them to identify any object or files that are causing bottlenecks.
  • Fragmentations and Defragmentations.
  • Identify the optimal settings of your database files and tables to reduce fragmentation and reduce them.
  • Backup and Recovery health Check.Review all backup & recovery settings and procedures of your databases and understand the functions of the respective databases.
  • Log Reviews (Windows Event Logs, SQL Server Error Logs and Agent Logs).
  • Logs reveal many hidden facts. Identity the critical errors and resolve them.
  • Hardware Review.
  • Review the hardware and and verify that it positively impact the performance or scalability of the database.
  • DBCC Best Practices Implementations.
  • There are few DBCC commands to be avoided and few very crucial for system. Understand the usage of DBCC FREEPROCCACHE, DBCC SRHINKDATABASE, DBCC SHRINKFILE, DBCC DROPCLEANBUFFER, DBCC REINDEX, as well as the usage of few system stored procedures like SP_UPDATESTATS. If you are currently using any of the above mentioned and a few other DBCC maintenance task commands carefully review their usage.
  • Deadlock Detection and Resolutions Hands-On.
  • Detecting deadlock is not very difficult, but to learn the tips and trick to resolve them requires an understanding of the issue and some experience. Understand the locking mechanism and resolve them.
 56.What are the types of indexes available with SQL Server?
There are basically two types of indexes that we use with the SQL Server. Clustered and the Non-Clustered.

57.When do we use the UPDATE_STATISTICS command?
This command is basically used when we do a large processing of data. If we do a large amount of deletions any modification or Bulk Copy into the tables, we need to basically update the indexes to take these changes into account. UPDATE_STATISTICS updates the indexes on these tables accordingly.

58.Which TCP/IP port does SQL Server run on?
SQL Server runs on port 433 but we can also change it for better security.

59.From where can you change the default port?
From the Network Utility TCP/IP properties –> Port number.both on client and the server.

60.What is the use of DBCC commands?
DBCC stands for database consistency checker. We use these commands to check the consistency of the databases, i.e., maintenance, validation task and status checks.

61.Can you give me some DBCC command options?
(Database consistency check) - DBCC CHECKDB - Ensures that tables in the db and the indexes are correctly linked.and DBCC CHECKALLOC - To check that all pages in a db are correctly allocated. DBCC SQLPERF - It gives report on current usage of transaction log in percentage. DBCC CHECKFILEGROUP - Checks all tables file group for any damage.

62.What command do we use to rename a db?
sp_renamedb ‘oldname’ , ‘newname’

63.Well sometimes sp_reanmedb may not work you know because if some one is using the db it will not accept this command so what do you think you can do in such cases?
In such cases we can first bring to db to single user using sp_dboptions and then we can rename that db and then we can rerun the sp_dboptions command to remove the single user mode.

64.What is a Join in SQL Server?
Join actually puts data from two or more tables into a single result set.

65.Can you explain the types of Joins that we can have with Sql Server?
There are three types of joins:
  • Inner Join
  • Outer Join
  • Cross Join
66.When do you use SQL Profiler?
SQL Profiler utility allows us to basically track connections to the SQL Server and also determine activities such as which SQL Scripts are running, failed jobs etc.

67.What is a Linked Server?
Linked Servers is a concept in SQL Server by which we can add other SQL Server to a Group and query both the SQL Server dbs using T-SQL Statements.

68.Can you link only other SQL Servers or any database servers such as Oracle?
We can link any server provided we have the OLE-DB provider from Microsoft to allow a link. For Oracle we have a OLE-DB provider for oracle that microsoft provides to add it as a linked server to the sql server group.

69.Which stored procedure will you be running to add a linked server?
sp_addlinkedserver
sp_addlinkedsrvlogin

70.What are the OS services that the SQL Server installation adds?
MS SQL SERVER SERVICE, SQL AGENT SERVICE, DTC (Distribution transac co-ordinator)

71.Can you explain the role of each service?
SQL SERVER - is for running the databases
SQL AGENT - is for automation such as Jobs, DB Maintanance, Backups
DTC - Is for linking and connecting to other SQL Servers

72.How do you troubleshoot SQL Server if its running very slow?
First check the processor and memory usage to see that processor is not above 80% utilization and memory not above 40-45% utilization then check the disk utilization using Performance Monitor, Secondly, use SQL Profiler to check for the users and current SQL activities and jobs running which might be a problem. Third would be to run UPDATE_STATISTICS command to update the indexes.

73.Lets say due to N/W or Security issues client is not able to connect to server or vice versa. How do you troubleshoot?
First I will look to ensure that port settings are proper on server and client Network utility for connections. ODBC is properly configured at client end for connection ——Makepipe & readpipe are utilities to check for connection. Makepipe is run on Server and readpipe on client to check for any connection issues.

74.What are the authentication modes in SQL Server?
Windows mode and mixed mode (SQL & Windows).

75.Where do you think the users names and passwords will be stored in sql server?
They get stored in master db in the sysxlogins table.

76.What is log shipping? Can we do logshipping with SQL Server 7.0
Logshipping is a new feature of SQL Server 2000. We should have two SQL Server - Enterprise Editions. From Enterprise Manager we can configure the logshipping. In logshipping the transactional log file from one server is automatically updated into the backup database on the other server. If one server fails, the other server will have the same db and we can use this as the DR (disaster recovery) plan.

77.Let us say the SQL Server crashed and you are rebuilding the databases including the master database what procedure to you follow?
For restoring the master db we have to stop the SQL Server first and then from command line we can type SQLSERVER –m which will basically bring it into the maintenance mode after which we can restore the master db.

78.What is BCP? When do we use it?
BulkCopy is a tool used to copy huge amount of data from tables and views. But it won’t copy the structures of the same.

79.What should we do to copy the tables, schema and views from one SQL Server to another?
We have to write some DTS packages for it.
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