8 Replies Latest reply: Apr 15, 2011 8:17 AM by Oscar Ortiz RSS

    QVD

    Logesh Jayaraman

      Hi,

      I have a query on the QVD tables.

      When the data is stored in QVD files either through Buffer or the Store Statement. Does the data is stored in RAM or it will be there in the hard disk?

      As per the documentation it is given as it will be used to store the slow changing data to reduce the load time and for incremental upload . But if the data is stored in RAM. Then the same cane be done through load statement.

      Please correct me if i am wrong and tell me the advantage of QVD

       

        • QVD
          Neil Miller

          QVD files store all of the data in a file. They are not in RAM as they are essentially permanent. In your application, you load the data into RAM just like you would from an Excel file or database. In some cases the QVD can be an optimized load, which greatly decreases load times.

          QVDs have many advantages, but once they are loaded into your application, the results shouldn't be much different than data loaded from other sources.

            • QVD
              Logesh Jayaraman

              Thanks NMiller,

              Since the QVD can be created using the Buffer and the Store statements. While using the Buffer keyword to create the QVD the data will be there in both RAM and QVD or only in QVD. I think if we are using the Store statement to create the QVD the data will not be there in RAM.

              Please help me to understand...........

                • QVD
                  Neil Miller

                  We use separate applications to build our QVDs. These applications load data from the databases and store it in a QVD, but don't do anything else (no sheet objects, charts, etc.). When these applications are reloaded, the data is in the QVD and in RAM. Once the QVDs are built, these applications can then be closed, freeing up the RAM.

                  We then go to our front end applications. These applications don't access the databases, but instead load all data from the QVDs. When these applications are reloaded (from QVD), the data is once again back in RAM and it is here where we are building our charts and such.

                  When I build a QVD building application, I make sure that it has no data stored in memory, to keep the file sizes down. I'll build the load script until it is working how I want and save the file empty. Then I will reload the application, which writes the data to QVD, but I do not save afterwards. This ensures that the QVD building application is empty and the filesize is small.

                    • QVD
                      John Stubblefield

                      Can someone help me understand what tool I should use to generate the QVD files?

                      I know that in my final report (qvw), I should just reference those QVD files so report reload would be optimized. However, I need to know how I should reload my QVD files daily?

                      QVD files are simply my fact tables - ie select * from FactBillingPeriod

                      I want to create QVD files whenever my fact tables are populated, so a batch process would be ideal, but let me know what are the best practice tools to use to daily re-build QVD files.

                      Your help is much appreciated!

                • QVD

                  QVD is the preferred format to store a file that has to be used by a Qlikview application.

                  They are incredibly fast to reload. A 10 million line file may be loaded in some seconds. In dev, the time saved may be significant.

                  • QVD
                    Oscar Ortiz

                    Using the Store statement or the Buffer statement will create a QVD file on the hard disk. The difference between the two statements is where QlikView will write the file to. With the Store statement you can control where the QVD file is written to. With the buffer statement, Qlikview decides where the QVD file is written to. You can check where this is written by going to User Preferences -> Locations and view the QVD Buffers location. This is where the QVD's are stored. These are stored using an encrypted file name.

                    Hope this information helps you.

                    Oscar

                      • QVD
                        John Stubblefield

                        So the best practice is to simply re-create QVDs in the final QVW report right?

                        I thought there's a better tool to re-create the QVDs, and in the final QVW report, just reference the QVDs that's already created to speed up the process.

                        If I want to automate the QVDs, do I just simply run the batch script with /r option?

                        Appreciated!

                          • QVD
                            Oscar Ortiz

                            Normally, your using your QVD for your final QVW. So you want to build your QVD's before getting to that point. Usually what I would do is like NMiller said. Use a seperate QVW to build the QVD's that your going to use in your final QVW. So I would have a QVW to build the data model that I'm going to use in my final user presentation QVW.

                            As far as automating you can setup a batch job to do that, or you could use Publisher to schedule it for you.

                            Hope this helps...

                            Oscar