Hi
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. QVD files can be read in two modes: standard (fast) and optimized (faster). The selected mode is determined automatically by the QlikView script engine. Optimized mode can be utilized only when all loaded fields are read without any transformations (formulas acting upon the fields), though the renaming of fields is allowed. A WHERE clause causing QlikView to unpack the records will also disable the optimized load. A QVD file holds exactly one data table and consists of three parts: A well formed XML header (in UTF-8 char set) describing the fields in the table, the layout of the subsequent information and some other meta-data. Symbol tables in a byte stuffed format. Actual table data in a bit-stuffed format.
QVD: Database file ; saves an uncompressed "RAM image" representation of a QlikView table as it was stored in memory when open in QlikView; allows the database to be opened and loaded into memory quickly.
When a QVD file is open, QlikView houses the database in memory instead of on disk, which allows for fast data queries and computation. Therefore, QVD files are loaded directly into memory when opened in the software.
