Performance vs size of qvd

[yelin_nyu]

i have a qvd that's around 7GB, the qvw that consumes that qvd is about 2.5GB, and my computer's RAM is about 12GB. The compression for the qvw is set at high. Every time I work on the document, it would use about 9-11+ GB of my RAM.

1. Can someone explain to me why it uses so much RAM?

2. How does the size of qvd affect the performance of qvw? I move many expressions into the script, and made the qvd even bigger. So I want to know at what point the calculation on front end actually would be better than calculation in script.

[rwunderlich · Accepted solution]

See this blog post

http://qlikviewnotes.blogspot.com/2011/03/qlikview-compression.html

for an explanation of file sizes and the relationship to RAM sizes.

QVDs are uncompressed, so a 7GB QVD will require at least 7GB of RAM, so your  RAM usage look reasonable.

To reduce the RAM requirements, you'l want to reduce the size of the fields in the QVD. You can do this by reducing the cardinatility -- the number of unique values -- of fields. For example, splitting timestamps into seperate Date and Time fields.

There are two tools you can use to identify field sizes.

1. Create a mem file and process with QV Optimizer. You can find a copy of QV Optimizer on the Forum.

2. Use the DocumentAnalyzer tool (http://robwunderlich.com/downloads/) against the consuming QVW. DocumentAnalyzer will identify the field sizes, and will also identify what fields are unused in your screen objects. You may be able to reduce the QVW RAM requirements by dropping unused Fields.

-Rob

http://masterssummit.com

http://robwunderlich.com