Hi Robert,
Robert Luberda wrote:
I'm forwarding bug report I got during my holidays.
I can reproduce the behaviour with sysstat 7.0.0.
I haven't checked however if the attached patch is correct and works.
<SNIP>
sar -s hh:mm:ss should return data after the specified time, however
it effectively skips the first record:
# sar -d |tail -n 5
14:06:08 dev8-0 0.92 0.00 18.54 20.22 0.00 0.60
0.18 0.02
14:07:08 dev8-0 0.58 0.00 13.20 22.63 0.00 0.23
0.20 0.01
14:08:08 dev8-0 1.57 0.00 36.26 23.15 0.00 1.52
0.17 0.03
14:09:08 dev8-0 0.77 0.00 17.87 23.30 0.00 0.22
0.09 0.01
Average: dev8-0 0.89 0.00 20.64 23.19 0.00 0.75
0.22 0.02
# sar -d -s 14:08:00
Linux 2.6.8-2-686 (IS-844) 20/07/06
14:08:08 DEV tps rd_sec/s wr_sec/s avgrq-sz avgqu-sz
await svctm %util
14:09:08 dev8-0 0.77 0.00 17.87 23.30 0.00 0.22
0.09 0.01
Average: dev8-0 0.77 0.00 17.87 23.30 0.00 0.22
0.09 0.01
# sar -d -s 14:09:00 |tail
Linux 2.6.8-2-686 (IS-844) 20/07/06
This behavior of sar may seem a bit ambiguous, I must admit, but it's
not a bug. Here is the explanation:
1) First, sar only displays stats on a complete interval of time. So if
you set the starting time to 14:08:00 in the example above, sar will
begin to display the stats at 14:08:08.
2) Then, the values displayed by sar are not instantaneous values, but
rather values calculated on an interval of time. The stats displayed at
time T are calculated on the interval ]T-dt;T] where dt is the sampling
interval. That's why when you enter "-s 14:08:00" on the command line,
the first line of stats displayed is for 14:09:08 which is actually the
stats calculated from 14:08:08 to 14:09:08... and which is what you
asked for (OK, to be very accurate, the interval from 14:08:00 to
14:08:08 is missing, but sar doesn't know how to compute the stats for
it since it is only a fraction of the interval.)
Regards,
--
Sébastien Godard (sysstat <at> wanadoo.fr)
http://perso.orange.fr/sebastien.godard/
