QVD compression logic

[#1]

Hi All,
I have created QVD file and also i have created qlikview file extracted data from database directly. But i saw the huge difference in size of the Qlik view file and QVD file. In the manual they had mentioned 90% compression will happen in QVD file. I would like to know how QVD compress this much. What compression logic they have used?

Where can i find those stuffs?

Thanks,
Raghu.

[#2 · Accepted solution]

Hi Raghu,

QVD files are not compressed, in fact they are text files with an XML header followed by bit-stuffed separated data records, column by column. The QlikView application with extension QVW is the one that is compressed.

Regards,

Mark

[#3]

Mark,

As you said "QVW is the one that is compressed", so QVD will consume more memory. I mean size of the QVD is more than QVW file. What is the use of creating QVD?

-Raghu

[#4]

Raghu,

The use of creating QVD files has as main purpose to store data from a data source in a format that is faster to load. This can be used for example in incredemental reloads where a user doesn't want to load all data from its data source but only the new data. The other (old) data can be loaded from the QVD. This results in faster reloads, but can only be used if the data source has many records that are not changing any more. Hope this helps you.

regards Mark

[#5]

Thanks Mark,

So create a QVW document from QVD file we need 3 documents

1) We need a QVW doc to create a QVD file. So 2 files

2) create qlikview file using QVD file.

Am i right.

Regards,

-Raghu

[#6]

Yes, generally you split the process into two parts, first is getting the data from conventional sources and storing it in QVDs, and second step is creating the main application which loads from these QVD files.

[#7]

Thanks for all your answers

Thanks,

Raghu.