It is not easy to compare events on a pgbench runs (oops, the tps is down) with for instance events in postgres log, so as to figure out what may have cause a given glitch.
This patches adds an option to replace the "time since pgbench run started" with a timestamp in the progress report so that it is easier to compare timelines.
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?
