I have 2 indexes with names - source_index, destination_index

Both indexes have same mappings.

I have written following code for making reindex and search requests -

@Autowired
RestHighLevelClient client;

public BulkByScrollResponse reIndexElasticResponse(ReindexRequest reindexRequest){
    BulkByScrollResponse reindexResponse = null;
    try{
      reindexResponse = client.reindex(reindexRequest,RequestOptions.DEFAULT);
    } catch (IOException e){
      throw new RuntimeException(e);
    }
    return reindexResponse;
}

public SearchResponse searchElasticResponseByScrollAPI(SearchScrollRequest searchScrollRequest) {
    SearchResponse searchResponse = null;
    try {
      searchResponse =  client.scroll(searchScrollRequest,RequestOptions.DEFAULT);
    } catch (IOException e) {
      throw new RuntimeException(e);
    }
    return searchResponse;
}

Now my application is reindexing only selected records from source_index to destination_index. And just after reindexing request, I am running one search query on destination_index.

The problem is that my search query is not giving me correct response as I think that reindexing request is not working in synchronous manner. If I use Thread.sleep(5000); after my reindexing request then my search query gives me correct result.

reIndexElasticResponse(reindexRequest);
Thread.sleep(5000);
searchElasticResponseByScrollAPI(searchScrollRequest);

The above code will work fine. But if I comment Thread.sleep(5000) then search query doesn't give expected output.

I want my program to wait until all the records are reindexed and then run the search query on destination_index