Wednesday, 27 April 2011

SSIS Interview Questions

1.  What Is the Control Flow?
                       
                                 In SSIS a workflow is called a control-flow. A control-flow links together our modular data-flows as a series of operations in order to achieve a desired result.

                                 A control flow consists of one or more tasks and containers that execute when the package runs. To control order or define the conditions for running the next task or container in the package control flow, you use precedence constraints to connect the tasks and containers in a package. A subset of tasks and containers can also be grouped and run repeatedly as a unit within the package control flow.

                                 SQL Server 2005 Integration Services (SSIS) provides three different types of control flow elements: containers that provide structures in packages, tasks that provide functionality, and precedence constraints that connect the executables, containers, and tasks into an ordered control flow.

2.  What is a Data Flow?

                                A data flow consists of the sources and destinations that extract and load data, the transformations that modify and extend data, and the paths that link sources, transformations, and destinations. Before you can add a data flow to a package, the package control flow must include a Data Flow task. The Data Flow task is the executable within the SSIS package that creates, orders, and runs the data flow. A separate instance of the data flow engine is opened for each Data Flow task in a package.

                               SQL Server 2005 Integration Services (SSIS) provides three different types of data flow components: sources, transformations, and destinations. Sources extract data from data stores such as tables and views in relational databases, files, and Analysis Services databases. Transformations modify, summarize, and clean data. Destinations load data into data stores or create in-memory datasets.

3.   How do you do error handling in SSIS?
                              When a data flow component applies a transformation to column data, extracts data from sources, or loads data into destinations, errors can occur. Errors frequently occur because of unexpected data values.

                              For example, a data conversion fails because a column contains a string instead of a number, an insertion into a database column fails because the data is a date and the column has a numeric data type, or an expression fails to evaluate because a column value is zero, resulting in a mathematical operation that is not valid.

Errors typically fall into one the following categories:

-Data conversion errors, which occur if a conversion results in loss of significant digits, the loss of insignificant digits, and the truncation of strings. Data conversion errors also occur if the requested conversion is not supported.
-Expression evaluation errors, which occur if expressions that are evaluated at run time perform invalid operations or become syntactically incorrect because of missing or incorrect data values.
-Lookup errors, which occur if a lookup operation fails to locate a match in the lookup table.

Many data flow components support error outputs, which let you control how the component handles row-level errors in both incoming and outgoing data. You specify how the component behaves when truncation or an error occurs by setting options on individual columns in the input or output.

For example, you can specify that the component should fail if customer name data is truncated, but ignore errors on another column that contains less important data.


4.  How do you do logging in ssis?
 
                              SSIS includes logging features that write log entries when run-time events occur and can also write custom messages.

                             Integration Services supports a diverse set of log providers, and gives you the ability to create custom log providers. The Integration Services log providers can write log entries to text files, SQL Server Profiler, SQL Server, Windows Event Log, or XML files.

                            Logs are associated with packages and are configured at the package level. Each task or container in a package can log information to any package log. The tasks and containers in a package can be enabled for logging even if the package itself is not.

                           To customize the logging of an event or custom message, Integration Services provides a schema of commonly logged information to include in log entries. The Integration Services log schema defines the information that you can log. You can select elements from the log schema for each log entry.

To enable logging in a package
 

1. In Business Intelligence Development Studio, open the Integration Services project that contains the package you want.
2. On the SSIS menu, click Logging.
3. Select a log provider in the Provider type list, and then click Add.

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