DataReader vs. DataSet — What's the Difference?

A DataReader is a connected approach in ADO.NET, designed for reading data in a forward-only, read-only manner directly from a database. It's highly efficient for retrieving large volumes of data as it uses less memory, reading one row at a time. In contrast, a DataSet is a disconnected data structure in ADO.NET that holds one or more DataTables in memory, allowing for data manipulation without maintaining a constant connection to the database.

The DataReader provides a fast and efficient way to retrieve read-only data. It's ideal for scenarios where the data is processed sequentially and there is no need to navigate back. On the other hand, a DataSet, being an in-memory cache of data, offers more flexibility. It can be used to hold data from multiple sources, navigate between rows, and even update the data.

DataReader is more lightweight compared to DataSet since it doesn’t store data in memory, which makes it a better choice for applications where performance is critical, especially with large data sets. The DataSet, however, because of its in-memory data storage, is more memory-intensive but allows for operations like sorting, filtering, and updating, which are not possible with a DataReader.

DataReader requires an open connection to the data source for the duration of the data reading process, which can be a limitation in scenarios where connection resources are scarce or expensive. DataSet works in a disconnected mode, meaning it can interact with the data after the connection to the database is closed, thus conserving connection resources.

In terms of data update and synchronization, the DataSet supports complex operations like data binding, making it suitable for applications where data manipulation and interaction are necessary. DataReader, being a read-only stream, doesn't support updates to the data, making it solely appropriate for data retrieval purposes.