if you are using variables for the root or host properties in your SpecWorkspaceImpl spec file, the p4 plugin will update the workspace two times a build:

Host property: If it isn't set in the spec file it will set it to '' (blank) and then it will update then set the host value on the client spec to the currently running node host name.

Root property: If you are using a variable (e.g. ${WORKSPACE}) the root is first set to 'WORKSPACE' and then it is set to current workspace you have specified in your jenkinsfile (using the ws() task).

Although everything still syncs correctly, over time this results in thousands of revisions on the same workspace that hasn't really changed. This can have a significant impact on the ability to backup the given perforce server.

I think the whole client spec should be expanded/resolved before it "updates" the client spec. This should prevent the updating of a client spec on every build.

diff of client spec:
p4 diff2 //spec/client/jenkins-DREUK-Prod-DREUK-UT023-Dashing.HealthCheck-Ping-configscripts.p4s#31018 //spec/client/jenkins-DREUK-Prod-DREUK-UT023-Dashing.HealthCheck-Ping-configscripts.p4s#31019
==== //spec/client/jenkins-DREUK-Prod-DREUK-UT023-Dashing.HealthCheck-Ping-configscripts.p4s#31018 (text+C) - //spec/client/jenkins-DREUK-Prod-DREUK-UT023-Dashing.HealthCheck-Ping-configscripts.p4s#31019 (text+C) ==== content
46a47,48
> Host: DREUK-UT023
>
50c52
< Root: WORKSPACE
—
> Root: C:\JenkinsAgent\w\Dashing.HealthCheck-Ping\Tools\Prod

d:\P4\EAUK\CM\DREUK>p4 diff2 //spec/client/jenkins-DREUK-Prod-DREUK-UT023-Dashing.HealthCheck-Ping-configscripts.p4s#31019 //spec/client/jenkins-DREUK-Prod-DREUK-UT023-Dashing.HealthCheck-Ping-configscripts.p4s#31020
==== //spec/client/jenkins-DREUK-Prod-DREUK-UT023-Dashing.HealthCheck-Ping-configscripts.p4s#31019 (text+C) - //spec/client/jenkins-DREUK-Prod-DREUK-UT023-Dashing.HealthCheck-Ping-configscripts.p4s#31020 (text+C) ==== content
41c41
< Update: 2018/11/07 10:41:35
—
> Update: 2018/11/07 10:49:03
43c43
< Access: 2018/11/07 10:09:03
—
> Access: 2018/11/07 10:41:35
47,48d46
< Host: DREUK-UT023
<
52c50
< Root: C:\JenkinsAgent\w\Dashing.HealthCheck-Ping\Tools\Prod
—
> Root: WORKSPACE

d:\P4\EAUK\CM\DREUK>p4 diff2 //spec/client/jenkins-DREUK-Prod-DREUK-UT023-Dashing.HealthCheck-Ping-configscripts.p4s#31020 //spec/client/jenkins-DREUK-Prod-DREUK-UT023-Dashing.HealthCheck-Ping-configscripts.p4s#31021
==== //spec/client/jenkins-DREUK-Prod-DREUK-UT023-Dashing.HealthCheck-Ping-configscripts.p4s#31020 (text+C) - //spec/client/jenkins-DREUK-Prod-DREUK-UT023-Dashing.HealthCheck-Ping-configscripts.p4s#31021 (text+C) ==== content
46a47,48
> Host: DREUK-UT023
>
50c52
< Root: WORKSPACE
—
> Root: C:\JenkinsAgent\w\Dashing.HealthCheck-Ping\Tools\Prod

I have attached an example file spec implementation
I believe the following two classes are where all the work is done:

• org\jenkinsci\plugins\p4\client\ClientHelper.java - public void setClient(Workspace workspace)
• org\jenkinsci\plugins\p4\workspace\SpecWorkspaceImpl.java - public IClient setClient(IOptionsServer connection, String user)