for i in 1000 2000 3000 4000 5000
do
    echo "$i rows: "
    pos=`expr $i / 2`
    psql -a test <<EOF
\timing
explain analyze
SELECT
  x,
nth_value(x,$pos) IGNORE NULLS OVER w
FROM generate_series(1,$i) g(x)
WINDOW w AS (ORDER BY x ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING);
EOF

done | egrep "rows:|Time:" | egrep -v "Planning|Execution"|
    sed -e 's/rows: *//' -e 's/Time: //' -e 's/ms//'