In Web Intelligence, you can set the number of rows that the query provider should retrieve. This setting is called the Max rows retrieved. From the Webi user guide:
The Max rows retrieved query property determines the maximum number of
rows of data that are displayed when a query is run.
If you only need a certain amount of data, you can set this value to
limit the number of rows of data in your document.
Max rows retrieved is applied at the database level if the database
supports it. If not, rows are discarded after retrieval from the
database.
Note: this setting is linked to the query, not the document as a whole. In other words, if your document has multiple queries, you have to set the Max rows retrieved for each of them.