The @PLUGIN@ plugin allows to synchronize secondary indexes between two Gerrit instances sharing the same git repositories and database.
The plugin is installed in both instances and every time the secondary index is modified in one of the instances, i.e., a change is added, updated or removed from the index, the other instance index is updated accordingly. This way, both indexes are kept synchronized.
For this secondary index synchronization to work, http must be enabled in both instances and the plugin must be configured with valid credentials. For further information, refer to config documentation.