Replication

Replication is a set of technologies for copying and distributing data and database objects from one database to another. Replication is a desired option when we want to have the same data on multiple database servers. There are different types of replication and more info on Replication can be read from this MSDN library article.
Use:

• It is good option when we want to have multiple server updates with disconnected options. It can be near real time. It can also be used to implement load balancing for a database.

Recovery:

• Recovery Time Objective (RTO) - This could be immediate and only require re-pointing your application to a different server.
• Recovery Point Objective (RPO) - If there is no data loss (due to data deletion), there is minimal to no data loss during the failover. Because this is an exact copy of the primary database all transactions will be replicated to the mirror copy as they were done on the primary server.

Pros:

• Can be configured for individual database objects instead of the entire database.
• Enhanced tools available for configuration and troubleshooting.
• Provides near real time disaster recovery.
• It supports disconnected architecture, so it is beneficial for mobile users.
• Secondary copy could be used for near real-time reporting to offload reporting use on production database.

Cons:

• Reconfiguration may require manual intervention.
• Need to rely on distributor to push changes.
• Other items need to be handled outside of Replication such as logins, SQL Agent jobs, etc...
• It is more complicated to setup and maintain then the other options.
• SQL Server will need to be fully licensed for the secondary server.

High Availability Options for SQL Server 2008

Each SQL Server 2008 High Availability option addresses different risks. As we know, no "one" solution fits all. We need to review carefully the business requirements. Basically, we need to consider a few questions like:

• Is Automatic Failover required?
• What is the data granular level for the High Availability?
• How much data loss or downtime is accepted?
• Is the standby server needed to provide read access?
• What are the budget constraints?

The High Availability requirement may differ from client to client, some clients may need the database to be up and running 24X7 and others may require only during office hours. So based on the client criticality need we have to choose appropriate the High Availability option. Otherwise there will be unnecessary expenses in terms of money, performance and resource utilization.
It is also very important to know what options are available in the different SQL Server editions before planning for the actual implementation. The below table shows differences between Enterprise and Standard High Availability features.

HA Options	Enterprise	Standard
Clustering	16-node failover clustering	2-node failover clustering
Database Mirroring	Full Support	Partial Support (Single Threaded, Safety Full Only)
Log Shipping	Full Support	Full Support
Replication	Full Support	Oracle Publishing not supported.

To summarize:

• Failover Clustering is an ideal selection if there is no budget constraint.
• Database Mirroring is alternative choice with minimal down time, because of automatic failover.
• Log Shipping is a good selection if we want to have multiple secondary servers.
• Replication is a good selection when there is the need to duplicate some of the data, send the data to multiple servers or for disconnected architecture support.
• Multiple options can be used, if there is a need to further protect from failures.
• This is not a complete list of all pros and cons for each option, but I hope this gives you a starting point on which technology to consider for your environment.

Log Shipping

Log Shipping provides database redundancy by sending transactional log backups periodically to a standby server or servers for the entire database. Transaction logs are automatically backed up, copied, and restored on the standby server(s). If the active server goes down, the standby server can be brought up by restoring any remaining shipped logs and then the database is recovered for use. More info on Log Shipping can be read from this MSDN library article.
Use:

• It is good option when we want to have multiple secondary failover servers for a database.

Recovery:

• Recovery Time Objective (RTO) - Failover is manual for this option, so this will take as long as it takes you to get the secondary server up and running.
• Recovery Point Objective (RPO) - If there is no data loss (due to data deletion), there is minimal to no data loss during the failover. Because transaction backups are applied to the secondary server all transactions will be replicated as they were done on the primary server. If you delay applying the transaction logs you could do a point in time recovery right before an accidental deletion of data occurred.

Pros:

• Log shipping can be configured to multiple standby servers.
• Can use compressed backup feature to limit network bandwidth
• It includes all the database objects along with their schema changes.
• By specifying Log Shipping in short interval, it can be near real-time database.
• Can be setup to use secondary server for read only activity
• No additional cost, except for the need to have another available server for the secondary copy.
• Can delay when the logs get applied to secondary server to help minimize data loss in the event of accidental data deletion (point in time recovery)
• If secondary server is used in a passive mode (only for failover), additional SQL Server licensing is not needed.

Cons:

• There is no automatic failover.
• Other items need to be handled outside of Log Shipping such as logins, SQL Agent jobs, etc...
• Requires additional storage for log backups and shipped copy
• If standby copy is used for read only, SQL requires exclusive access to the database when a log backup is restored

List of Sql Server Interview Questions Part 1

What is normalization? 

A relational database is basically composed of tables that contain related data. So the Process of organizing this data into tables is actually referred to as normalization. 

What is a Stored Procedure? 

A set of T-SQL statements combined to perform a single task of several tasks. Its basically like a Macro so when you invoke the Stored procedure, you actually run a set of statements. 

Give an example of Stored Procedure? 

sp_helpdb , sp_who2, sp_renamedb are a set of system defined stored procedures. 

We can also have user defined stored procedures which can be called in similar way. 

What is a View?

If we have several tables in a Database and we want to view only specific columns from specific tables we can go for views.  It would also suffice the needs of security some times allowing specfic users to see only specific columns based on the permission that we can configure on the view. Views also reduce the effort that is required for writing queries to access specific columns every time. 

What is an Index? 

When queries are run against a Database, an index on that 

Database

 basically helps in the way the data is sorted to process the query for faster and data retrievals are much faster when we have an index. 

What is a Trigger? 

 Triggers are used to implement business rules. Triggers is similar to stored procedures.

 The difference is that it can be activated when data is inserted or updated or deleted from a table in a database. 

What are the types of indexes available with SQL Server?

 There are two types of indexes that we use with the SQL Server. Clustered and the Non-Clustered. 

What is the difference between Clustered and a non-Clustered Index?

The difference is that, Clustered index is unique for any given table and we can have only one clustered index on a table. The leaf level of a clustered index is the actual data and the data is resorted in case of clustered index. Whereas in case of non-clustered index the leaf level is actually a pointer to the data in rows so we can have as many non-clustered indexes as we can on the db. 

What are Cursors? 

Cursors help us to do an operation on a set of data that we retreive by commands such as Select columns from table. For example : If we have duplicate records in a table we can remove it by declaring a cursor which would check the records during retreival one by one and remove rows which have duplicate values. 

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. 

Which TCP/IP port does SQL Server run on? 

SQL Server runs on port 1433 but we can also change it for better security. 

From where can you change the default port?

From the Network Utility TCP/IP properties –> Port number.both on client and the server. 

What is the difference between DELETE & TRUNCATE commands? 

Delete command removes the rows from a table based on the condition that we provide with a WHERE clause. Truncate will actually remove all the rows from a table and there will be no data in the table after we run the truncate command. 

Can we use Truncate command on a table which is referenced by FOREIGN KEY? 

 No. We cannot use Truncate command on a table with Foreign Key because of referential integrity. 

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. 

give 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 CHECKFILEGROUP - Checks all tables file group for any damage. 

DBCC SQLPERF - It gives report on current usage of transaction log in percentage. 

What command do we use to rename a Database? 

sp_renamedb ‘oldname’ , ‘newname’ 

What do you mean by COLLATION?

Collation is basically the sort order. There are three types of sort order

Dictionary case sensitive, Dictonary - case insensitive and Binary. 

Well sometimes sp_renamedb 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. 

What is the difference between a HAVING CLAUSE and a WHERE CLAUSE?

 Having Clause is basically used only with the GROUP BY function in a query.

WHERE Clause is applied to each row before they are part of the GROUP BY function in a query. 

What is a Join in SQL Server?

Join actually puts data from two or more tables into a single result set. 

Explain the types of Joins that we can have with Sql Server?

There are three types of joins: Inner Join, Outer Join, Cross Join 

When do you use SQL Profiler? -

SQL Profiler utility allows us to track connections to the SQL Server and also determine activities such as which SQL Scripts are running, failed jobs etc.. 

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. 

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. 

Which stored procedure will you be running to add a linked server? 

 sp_addlinkedserver, sp_addlinkedsrvlogin 

What are the OS services that the SQL Server installation adds? 

MS SQL SERVER SERVICE, SQL AGENT SERVICE, DTC (Distribution transaction co-ordinator) 

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 

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 

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. 

What are the authentication modes in SQL Server?

Windows mode and mixed mode (SQL & Windows). 

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. 

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. 

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. 

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. 

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. 

System Stored Procedure sp_recompile

Whenever you add new indexes to a table or modify its structure extensively is a good practice to recompile all stored procedures involved with that table, so the queries included on those stored procedures could be reoptimized.

The following example is using the Employees table of AdventureWorks database.

USE AdventureWorks;
GO
EXEC sp_recompile N'HumanResources.Employee';
GO

Resulting message for this instruction should be:
Object 'HumanResources.Employee' was successfully marked for recompilation.