Wednesday, January 13, 2010

Looks Funny

Looks funny is a term with specific meaning. That meaning is:
"Has a result or value that appears incorrect but has not been shown to be wrong".

Something that looks funny might really be a problem. Alternatively, it might be something that is perfectly correct, but your understanding needs some clarification.

For example, we were testing data ingest rates, and we got results like these:
Plain text = 49 MB/s
Office = 48 MB/s
VMWare Images = 76 MB/s

That VMWare image number "looks funny". We didn't yet know it was wrong, but it was certainly not in line with our other results. After digging in, we identified that a significant portion of the time was being spent with opening files. So in data sets made up of relatively many smaller files (plain text and office), the amount of time spent opening files as a percent of the total ingest time was high. For larger files (VMWare images), the amount of time spent opening files was lower as a percent of total ingest time, which resulted in an overall faster speed.

Other times, "looks funny" is the first sign of a bug. For example, we noticed that sometimes doing actions was a bit slow. "Sometimes", by the way, is a general sign that you might have something that "looks funny". It took a long time to track it down, but it eventually turned out to be a background process running at too high a priority. Most of the time that didn't cause a problem, but every once in a while there would be enough other stuff going on that the thing you were trying to do had to wait around for a while.

As you're testing, keep an eye out. Something that looks funny is probably worth following up.

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