What is QVD format

[Anonymous]

hi,
I am trying to understand QVD file format. So far i found following
QVD files consist of three parts
1. XML header
2. Symbol tables in a byte stuffed format.
3. Actual table data in a bit-stuffed format.

Most of people know what XML is and some may also know about bit and byte Stuffing (not me).
But I want to know what is actually bit and byte stuffing?
and how this helps Qlikview database engine to speed up the process?

Regards,

Mu

[#2]

Hi Muhammad

a byte is an octet

a byte holds 8 bits

a QVD file is a special file under specific QV format.

You can build it from a QVW and read it with a QVW

best regards

Chris

[selvakumarsr]

QVD : Stands for Qlikview Data (One of the optimize layer of data which has been fetched from the database, qvd is a patent technology of qliktech and qlikview applications reads data 100 time faster as compared to any other sources because data get stores in optimized format. Only Qlikvew application can read the data from QVD. Its always better to fetch the data from from database first and then load the data into your application)

see this post..QVD, QVW and QVX

Selva

[Anonymous]

Thanks for prompt reply but i want to know what is special file? and what is specific QV format?

[Anonymous]

Thanks Selva,

but I want to understand why and how QVD is 100 times faster as compare to other file format?

[ThornOfCrowns]

The QVD holds a compressed version of the data used to make it. When you use a QVD to retreive data it pushes this compressed format directly into memory. If your QVD is optimised, it can be up to 100 times quicker that a 'normal' database load.

Think of it as the difference between a JPEG and a BMP of a pure white square 10x10 pixels.

Very simply, JPEG compresses the data, i.e. it holds one value for RGB(255,255,255) and then holds 99 smaller pointers to this location for all other instances of RGB(255,255,255) , resulting in a small file size.

Whereas the BMP holds all data on a 1 to 1 basis, i.e. 100 separate large bits of imformation.