If you ever need to drop lines from a stream of text randomly, you can use this simple and short awk command:
Example: cat file | awk '{if (int(rand()*100) < 10) print $0;}'
This example keeps only 10%. You can change the 10 to any other percentage to drop more or less.
As an example, I use this to warmup my MediaWiki installation before doing a real WikiBench benchmark:
cat benchmarks/1pct.trace | head -n 100000 | grep "\-$" | \
awk '{if (int(rand()*100) < 10) print $0;}' | ./start_controller.sh -verbose
