Similar to @Txangel's probabilistic solution but approaching 100x faster.
perl -ne 'print if (rand() < .01)' huge_file.csv > sample.csv
If you need high performance, an exact sample size, and are happy to live with a sample gap at end of the file, you can do something like the following (samples 1000 lines from a 1m line file):
perl -ne 'print if (rand() < .0012)' huge_file.csv | head -1000 > sample.csv
.. or indeed chain a second sample method instead of head.