Hi Everyone, I have a very basic question about how Qlik works
As far as I understand this is how the data refresh takes place
a) QVW defines what the report view/selections need
b) QVD then defines what data is needed to fulfill the QVW
c) A subset of data from the source is then fetched on the defined crequency to fulfill the QVD data need
Questions I have are below
1) Is the QVD created automatically from what's defined in the QVW
2) OR is the QVD also developed just like the QVW. If so what do you develop on the QVD?
3) Is all data from the QVD loaded onto the QVW?
4) OR are data loaded on demand based on user demand from the QVD onto the QVW?
5) Does each user selection create their own cache or are all selections made by pool of users cache generally onto the memory of the server where the QVW is accessed from?
Hope someone can answer these from me? I know these are basic questions butit is important for me to understand the underlying mechanics of how Qlik works. Unfortunately I couldn't find any single source which can describe this clearly.
1) You define in the QVW the charts, layout and filter you want to display, yes
2) No. QVD is a optimized storage for a table for QlikView. You can or cannot use these files and the result in the layout and front-end will make no difference for the user. It is for your convenience as developer
3) No, as you can see below, you define which table (or columns of a table) are stored into each QVD, if any at all.
To your questions:
1) No, you specify the contents in columns and rows of the QVD in the script. The QVD is "simply" a temporary storage of a table, while the QVW is the entire application including the loading script, the data iself, visualizations and security.
2) See help files at help.qlik.com for STORE and LOAD
3) Again, the QVD is yet another source of data for QlikView, as such, you decide which contents of the table stored into the QVD file are in the QVW application. You can use JOINs, KEEPs, WHERE, etc. on the QVD as you would do with any other data source.
4) Yep, you decide what to load from each QVD
5) QlikView has several levels of cache, so to speak. The user session keeps cached all results, but there is also a cache for the application, for instance, if a user sees a chart for Sum(Amount) per country, this calculation is done and stored into the cache. The next user to see the same chart will retrieve from cache, which is even faster than from memory.
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