“Extract” is a word you’re going to hear a lot in Tableau. Extracts are one of the most powerful but overlooked tools in Tableau’s arsenal.
Tableau Data Extracts are snapshots of data optimized for aggregation and loaded into system memory to be quickly recalled for visualization. Extracts tend to be much faster than live connections, especially in more complex visualizations with large data sets, filters, calculations, etc.
For a deep dive into how Tableau extracts are created, check out Gordon Rose’s fantastic blog post on the subject.
When you create an extract from a local file (such as a .csv or an Excel workbook) or an on-premise database, you’re speeding up the workbook through optimization. As a result, Tableau doesn’t need the database to build the visualization. Instead, Tableau’s in-memory data engine queries the extract directly.
However, because an extract is a snapshot of the data, the extract will need to be refreshed to receive updates from the original data source, whether it is a local file or an on-premise database.
Live connections offer the convenience of real-time updates, with any changes in the data source reflected in Tableau. But live connections also rely on the database for all queries. And unlike extracts, databases are not always optimized for fast performance. With live connections, your data queries are only as fast as the database itself.
There are also more variables at play when using a live connection. Workbook speeds are affected by a variety of factors, including your network speed, traffic on that network, and any custom SQL.