QVD and QVX files

We have now gone through the process of loading data from traditional databases and simple table files. In this section, we will take a deeper look at the QVD and QVX file types, which are used by QlikView to store and read data in an optimized format.We will discuss a little more about both of these types, and the benefits and uses of each of them.

QVD files

QlikView Data (QVD) files are used to extract and store data into and from QlikView. This means that whichever table you read, from whichever database, you can store it in the QVD format before or after any transformations you perform on the table. The special characteristics of this file type are:

• It contains only one logical table.

• It uses a special algorithm to compress the data, achieving compression rates of up to 90 percent, depending on the fields' cardinality of the underlying data.

• When reading a QVD table file in QlikView, the loading speed is anywhere from 10 to 100 times faster than when loading from a database...