Generally, QVD's are one of the most important in any Qlikview deployment.
A QVD (QlikView Data) file is a file containing a table of data exported from QlikView. QVD is a native QlikView format and can only be written to and read by QlikView. The file format is optimized for speed when reading data from a QlikView script but it is still very compact. Reading data from a QVD file is typically 10-100 times faster than reading from other data sources.
Whenever we are are using to QVD as data source, we need to keep the Optimized load better reload times. But in some cases we didn't keep optimized loads especially if we are using filters with Where command.
Other hand , we can keep optimized loads in some scenarios:
LOAD * FROM QVDANAME.qvd (qvd) Where Match(REGION_NAME,'US','CANADA');
In the above case, we are loading the data only from US and CANADA region and this is unoptimized load. But we can load as Optimized load by using EXISTS key word with temp table.
First, create the Temp table with filters and use EXISTS key word in main QVD loading statement like below:
LOAD * INLINE [
LOAD * FROM QVDANAME.qvd (qvd) Where EXISTS (REGION_NAME) ;
DROP Table TEMP ;
Note: Please make sure that TEMP having the same field name which QVD have