Use milliseconds for consistency with the '%n' log_prefix patch currently submitted by Tomas Vondra in the CF.
sh> ./pgbench -P 1 -N -T 100 -c 2 starting vacuum...end. progress: 1.0 s, 546.0 tps, lat 3.619 ms stddev 4.426 progress: 2.0 s, 575.0 tps, lat 3.480 ms stddev 1.705
sh> ./pgbench -P 1 --progress-timestamp -N -T 100 -c 2 starting vacuum...end. progress: 1440328800.064 s, 549.0 tps, lat 3.602 ms stddev 1.698 progress: 1440328801.064 s, 570.0 tps, lat 3.501 ms stddev 1.704
I like the idea of the timestamp. But could just always print both the timestamp and the elapsed time, rather than adding another switch to decide between them?
I agree that an option for this purpose is on the heavy side.
I'm not sure how fine it would be, though: progress lines can already be a little bit long (under -R & -L) and I do not like wide terminal. Also, I see --progress as a "user friendly" easy to read feature to know how things are going during a run. A timestamp does not fall into this category: it is pretty ugly and unreadable, so it is really out of necessity that I'm resorting to that.
So I would rather keep the option because of the inelegance of having timestamps printed.
OK.
In the sgml, second should be plural in 'intead of the number of second since the'. And 'intead' should be 'instead'.
Also, in the usage message, I think the key piece of this is that it is Unix-epoch, not that it is ms resolution:
--progress-timestamp use a ms timestamp for progress
Maybe
--progress-timestamp use a Unix-like epoch timestamp for progress reporting