Re: pgbench throttling latency limit

On 2014-08-14 15:01:53 +0200, Fabien COELHO wrote:
>
> Add --limit to limit latency under throttling
>
> Under throttling, transactions are scheduled for execution at certain times.
> Transactions may be far behind schedule and the system may catch up with the
> load later. This option allows to change this behavior by skipping
> transactions which are too far behind schedule, and count those as skipped.
>
> The idea is to help simulate a latency-constrained environment such as a
> database used by a web server.

I was just trying to run tests with this, but as far as I can see it
doesn't really work:

pgbench postgres -M prepared -c 72 -j 72 -P 5 -T 3600 -R40000 -L100
...
progress: 240.0 s, 40191.8 tps, lat 1.250 ms stddev 0.965, lag 0.501 ms, 0 skipped
progress: 245.0 s, 39722.1 tps, lat 1.128 ms stddev 0.946, lag 0.435 ms, 0 skipped
progress: 250.0 s, 40074.5 tps, lat 1.059 ms stddev 0.745, lag 0.391 ms, 0 skipped
progress: 255.0 s, 40001.4 tps, lat 1.038 ms stddev 0.680, lag 0.377 ms, 0 skipped
progress: 260.0 s, 40147.6 tps, lat 1.161 ms stddev 0.950, lag 0.448 ms, 0 skipped
progress: 265.0 s, 39980.1 tps, lat 1.186 ms stddev 0.862, lag 0.457 ms, 0 skipped
progress: 270.0 s, 40090.9 tps, lat 1.292 ms stddev 1.239, lag 0.544 ms, 0 skipped
progress: 275.0 s, 33847.8 tps, lat 26.617 ms stddev 41.681, lag 25.317 ms, 26698 skipped
progress: 280.0 s, 20237.9 tps, lat 96.041 ms stddev 11.983, lag 92.510 ms, 97745 skipped
progress: 285.0 s, 24385.0 tps, lat 94.490 ms stddev 10.865, lag 91.514 ms, 80944 skipped
progress: 290.0 s, 27349.6 tps, lat 92.755 ms stddev 10.905, lag 90.136 ms, 62268 skipped
progress: 295.0 s, 28382.1 tps, lat 92.752 ms stddev 10.238, lag 90.212 ms, 58253 skipped
progress: 300.0 s, 28798.3 tps, lat 92.673 ms stddev 10.506, lag 90.172 ms, 56741 skipped
progress: 305.0 s, 29346.6 tps, lat 91.659 ms stddev 10.982, lag 89.210 ms, 53163 skipped
progress: 310.0 s, 30072.9 tps, lat 91.190 ms stddev 11.071, lag 88.802 ms, 48370 skipped
progress: 315.0 s, 30733.2 tps, lat 90.893 ms stddev 11.312, lag 88.548 ms, 47020 skipped
progress: 320.0 s, 31170.9 tps, lat 89.498 ms stddev 12.132, lag 87.192 ms, 43403 skipped
progress: 325.0 s, 33399.0 tps, lat 85.795 ms stddev 15.196, lag 83.639 ms, 32923 skipped
progress: 330.0 s, 22969.8 tps, lat 91.929 ms stddev 14.762, lag 88.805 ms, 84780 skipped
progress: 335.0 s, 18913.3 tps, lat 95.236 ms stddev 14.523, lag 91.444 ms, 104960 skipped
progress: 340.0 s, 20061.2 tps, lat 95.258 ms stddev 13.284, lag 91.660 ms, 100396 skipped
progress: 345.0 s, 20405.3 tps, lat 94.781 ms stddev 13.794, lag 91.255 ms, 98510 skipped
progress: 350.0 s, 20596.0 tps, lat 94.661 ms stddev 13.345, lag 91.189 ms, 95426 skipped
progress: 355.0 s, 13635.7 tps, lat 96.998 ms stddev 38.039, lag 91.691 ms, 132598 skipped
progress: 360.0 s, 16648.0 tps, lat 95.138 ms stddev 26.329, lag 90.809 ms, 117129 skipped
progress: 365.0 s, 18392.1 tps, lat 94.857 ms stddev 23.917, lag 90.980 ms, 106244 skipped

100k skipped transactions at a rate limit of 40k? That doesn't seem right.

(that's master server/pgbench as of 5be94a9eb15a)

Regards,

Andres