Recently, I had a job to clean up our Gerrit server. First of all, I have to find projects which we can deprecate and remove them.
Here is the solution how I found outdated Gerrit Projects.
Gerrit Administrator can use gerrit gsql command to access Gerrit backend database and query outdated projects. The below SQL can find projects whose lastest changes were updated 180 days ago.
The results could be the candidates of deprecating projects.