private VolumeGroup createVolumeGroup(final Connection connection,
                                          final List<Integer> oldVolumeIds) {
        final int id = currentGroupId.incrementAndGet();
        final String groupName = "Group " + id;
        createGroup(connection, id, groupName);

        LOGGER.info("Created index volume group (id {}, name {}) with old vol ids [{}]",
                id,
                groupName,
                oldVolumeIds.stream()
                        .map(Object::toString)
                        .collect(Collectors.joining(",")));

        return new VolumeGroup(id, groupName, oldVolumeIds);
    }
@return A map of index UUIDs to lists of the volumes they use. We'll need both, hence the map.
stroom-legacy/stroom-legacy-db-migration/src/main/java/stroom/legacy/db/migration/V07_00_00_1502__Index.java