Databases Reference
In-Depth Information
Click on the
XL
icon in the
Movie List
table to export the list of currently selected
movies to Excel.
A word of warning when exporting data
When viewing tables with a large number of rows, QlikView is very good
at only rendering those rows that are presently visible on the screen. When
Export values to Excel
is selected, all values must be pulled down into an
Excel file. For large data sets, this can take a considerable amount of time
and may cause QlikView to become unresponsive while it provides the data.
The technology and components
behind QlikView
Now that we have seen how QlikView works from the point of view of a business
user, it is time to get a little more technical. Let's take an in-depth look at the various
components that QlikView consists of.
One of the key elements of QlikView is that it utilizes an in-memory database.
Compared with a disk-based database, this offers a great advantage when it comes
to performance. While disk-access time is measured in milliseconds, RAM access
time is measured in nanoseconds, making it many orders of magnitude faster.
"But hold on—" you may say, "my hard disk has much more space than I have RAM
in my PC; won't that mean that I can only load limited amounts of data into memory?"
This is a very valid question. Fortunately, there are two factors which counter this
potential problem:
• Cheap memory and the advancement of 64-bit processors and operating
systems: While 1 megabyte of memory, in 1957, would have cost a staggering
US$ 411 million, nowadays, a gigabyte can be had for less than US$ 5 (source:
http://www.jcmit.com/memoryprice.htm
). Coupled with 64-bit operating
systems, which can address much larger amounts of RAM than 32-bit
systems (up to 2 terabyte on Windows 2008 R2), it is feasible and (relatively)
affordable to load huge amounts of data into RAM.
• Clever compression: QlikView utilizes some sophisticated compression
algorithms (and some common sense, such as de-duplicating data) to
significantly reduce the amount of memory that is required to store data.
Typically, on-disk data is compressed to 10 percent of its original size when
it is loaded into QlikView.
These two factors make it possible to create QlikView applications that contain
hundreds of millions—even billions—of records.
