What is "workspace polling" in the context of Jenkins?
The Git Jenkins plugin doc includes:
Fast Remote Polling
Fast Remote Polling is a feature that uses a speedy 'git ls-remote ...' command to perform the SCM polling action rather than having to a clone and fetch a local repository.
This feature is enabled by default as of versions 2.2+.
In the event that Fast Remote Polling is detected as being not possible (branches to build contains wildcards, etc), polling will fallback to requiring a workspace.
However, it is possible in some environments that Fast Remote Polling will not work due to the fact that it executes on the master and the master may not have a working Git installation.
A workaround for this is to add an additional behavior of Force polling using workspace to all jobs where you want to use SCM polling.
That means detecting changes by polling (git pull/git checkout) in a workspace vs. querying the remote repo with git ls-remote.
That was discussed in JENKINS-10131.