QVD and QVX files - Qlik View

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. When the table file is being read without applying any transformations, QlikView performs an optimized load (super-fast mode).

One of the main advantages of using QVD files is that, once you have a QVD on your disk, the table can be exploited by more than one QlikView application. This reduces the load on the database server, and optimizes QlikView resources and development time. This process is called QVD staging and is discussed further in Chapter (Advanced Data Transformation), Advanced Data Transformation.
The QVD file will also be particularly useful when dealing with Incremental Load scenarios which are discussed in Chapter (Advanced Data Transformation), Advanced Data Transformation.

QVX files

QlikView data eXchange (QVX) files are used for data input from external systems into QlikView. The main difference with respect to the QVD file is that QVX is a public format and can be created from external interfaces. It can be considered as the format in which custom data sources (described earlier in the chapter) send data to QlikView via the custom connector. Data retrieval becomes optimized when complying with QVX specifications, although not as optimized as QlikView's own QVD.

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