def verify_ids(doc_iter, es_host, index, doc_type=None, step=100000, ):
    '''verify how many docs from input interator/list overlapping with existing docs.'''

    index = index
    doc_type = doc_type
    es = get_es(es_host)
    q = {'query': {'ids': {"values": []}}}
    total_cnt = 0
    found_cnt = 0
    out = []
    for doc_batch in iter_n(doc_iter, n=step):
        id_li = [doc['_id'] for doc in doc_batch]
        # id_li = [doc['_id'].replace('chr', '') for doc in doc_batch]
        q['query']['ids']['values'] = id_li
        xres = es.search(index=index, doc_type=doc_type, body=q, _source=False)
        found_cnt += xres['hits']['total']
        total_cnt += len(id_li)
        out.extend([x['_id'] for x in xres['hits']['hits']])
    return out