SQL Server Integration Services (SSIS) Architecture
SQL Server Integration Services (SSIS) is a platform for data integration and workflow applications. It is a component of SQL Server and is used to extract, transform, and load data from various sources into destinations. Understanding the SSIS architecture is crucial for designing, developing, and managing efficient data integration solutions.
A simplified representation of the SSIS architecture.
Core Components of SSIS
The SSIS architecture can be broadly categorized into the following key components:
- SSIS Designer: A graphical user interface (GUI) integrated with SQL Server Data Tools (SSDT) or Visual Studio, used for designing SSIS packages.
- SSIS Runtime: The engine that executes SSIS packages. It manages the execution of tasks, data flow, and event handling.
- SSIS Engine: The core of the SSIS runtime, responsible for orchestrating package execution. It parses the package, manages connections, and invokes tasks.
- Tasks: The building blocks of an SSIS package's control flow. They perform specific actions, such as executing SQL statements, sending emails, or transferring files.
- Data Flow Task: A specialized task that facilitates the extraction, transformation, and loading of data. It contains a data flow pipeline.
- Data Flow Pipeline: Within the Data Flow Task, this pipeline consists of source components, transformation components, and destination components.
- Connection Managers: Objects that enable SSIS to connect to various data sources and destinations (e.g., SQL Server, flat files, Excel, OData).
- Event Handlers: Mechanisms for responding to events that occur during package execution, such as package start, task success, or errors.
- Log Providers: Components used to log execution events and status information for auditing and troubleshooting.
- Variables and Parameters: Used to store values that can be used and modified during package execution, allowing for dynamic package behavior.
- Expressions: Used to dynamically assign values to properties of SSIS objects.
Control Flow vs. Data Flow
SSIS packages have two distinct design surfaces:
- Control Flow: Defines the workflow of the package. It specifies the order in which tasks are executed, their dependencies, and the logic for conditional execution. Control flow is designed using tasks, precedence constraints, and event handlers.
- Data Flow: Defines the process of extracting, transforming, and loading data. It involves connecting to data sources, applying transformations to the data, and writing the transformed data to destinations. The Data Flow Task is the primary container for the data flow pipeline.
Key Architectural Concepts
- Package: The fundamental unit of work in SSIS. A package is a collection of tasks, data flow elements, connection managers, variables, and event handlers.
- Precedence Constraints: Connect tasks in the control flow, defining the execution order and conditions under which a subsequent task can run (e.g., success, failure, completion).
- Transactions: SSIS supports transactions to ensure data consistency. If an error occurs within a transaction, the entire transaction can be rolled back.
- Extensibility: SSIS can be extended through custom tasks, custom transformations, custom connection managers, and custom event handlers.
Execution Model
SSIS packages can be executed in several ways:
- Directly from SQL Server Data Tools (SSDT) or Visual Studio.
- By the SQL Server Agent.
- From the command line using
DTExec.exe. - Programmatically using the SSIS object model.
- Deployed to an SSIS Catalog or a file system.