Performance of ByteA: ascii vs binary

I did some benchmarking and in my setup there was major
performance difference.

I tested a ByteA column.

If I used ascii data the tests took 52 seconds.
If I used random binary data the test took 250 seconds.

binary data is (roughly) five times slower than ascii data?

Is this a know fact, or is there something wrong with my benchmark?

I used Python and psycopg2.

Regards,
   Thomas Güttler


-- 
Thomas Guettler http://www.thomas-guettler.de/
I am looking for feedback: https://github.com/guettli/programming-guidelines