undesired_contact_detector gets high load since Gazebo 9.16.0

[yosuke]

Gazebo 9.16.0 (2020-11-24) seems to publish contact messages (in gzmessage form) more frequently than the previous versions.
This results in undesired_contact_detector to be very heavy.

[yosuke]

Result of gz topic -z /gazebo/default/physics/contacts in Gazebo 9.9.0

Hz: 757.29
Hz: 3135.17
Hz: 294.77
Hz: 195.75
Hz: 571.19
Hz: 312.31

[yosuke]

Result of gz topic -z /gazebo/default/physics/contacts in Gazebo 9.16.0

Hz: 535.92
Hz: 449.76
Hz: 453.55
Hz: 673.86
Hz: 556.43
Hz: 590.84
Hz: 617.81
Hz: 818.10
Hz: 855.72
Hz: 836.09

The difference in Hz is not as large as expected.
May be contained data size in the message?

[yosuke]

Or maybe the reason is the stabilized frequency of message callbacks in over frequency situations.
Probably better to implement a call skipping function based on the timestamp (10Hz will be enough for contact detection).
The time stamp in the message is in the following format:

time {
  sec: 117
  nsec: 562000000
}

[yosuke]

CPU load is still high even if we lower the contact detection rate.