DVCS synchronisation uses extremely long-running SELECT

When dealing with DVCS accounts with large repositories, doing a full sync or add new accounts would cause the following long running query:

SELECT "ID" FROM public."AO_E8B6CC_CHANGESET_MAPPING" WHERE "ID" not in (select "CHANGESET_ID" from public."AO_E8B6CC_REPO_TO_CHANGESET")

This query is used when the DVCS Connector tries to deleting existing changesets before doing a full sync.