It looks like Elasticsearch is currently missing support for concurrent searching and that this is a major prospective optimization to reduce latency.

Digression: this is not the topic at hand but I personally consider the fork OpenSearch to be an historical tragedy of duplication of work and a segregation of improvements. What would be even more anti-utilitarist would be to blindly *ignore* each other advances towards making better search.

Lucene concurrent search APIs are probably among the most important feature/optimization currently not leveraged by Elasticsearch.
The fork OpenSearch has a [pull request](https://github.com/opensearch-project/OpenSearch/pull/1500) implementing support for it.

See also the [corresponding issue](https://github.com/opensearch-project/OpenSearch/issues/1286) 

I believe it would be great for end users if you could take inspiration from the PR and work on this feature.

Great blog about the Lucene feature:
https://blog.mikemccandless.com/2019/10/concurrent-query-execution-in-apache.html?m=1
See also those performance results:
https://engineeringblog.yelp.com/2021/09/nrtsearch-yelps-fast-scalable-and-cost-effective-search-engine.html
test/framework/src/main/java/org/elasticsearch/test/ESIntegTestCase.java
*/
    protected static IndicesAdminClient indicesAdmin() {
        return admin().indices();
    }
    public void indexRandom(boolean forceRefresh, String index, int numDocs) throws InterruptedException {
        IndexRequestBuilder[] builders = new IndexRequestBuilder[numDocs];
        for (int i = 0; i < builders.length; i++) {
            builders[i] = client().prepareIndex(index).setSource("field", "value");
        }
        indexRandom(forceRefresh, Arrays.asList(builders));
    }
    /**
     * Convenience method that forwards to {@link #indexRandom(boolean, List)}.
     */
    public void indexRandom(boolean forceRefresh, IndexRequestBuilder... builders) throws InterruptedException {
        indexRandom(forceRefresh, Arrays.asList(builders));
    }
    public void indexRandom(boolean forceRefresh, boolean dummyDocuments, IndexRequestBuilder... builders) throws InterruptedException {
        indexRandom(forceRefresh, dummyDocuments, Arrays.asList(builders));
    }
    /**
     * Indexes the given {@link IndexRequestBuilder} instances randomly. It shuffles the given builders and either
     * indexes them in a blocking or async fashion. This is very useful to catch problems that relate to internal document
     * ids or index segment creations. Some features might have bug when a given document is the first or the last in a
     * segment or if only one document is in a segment etc. This method prevents issues like this by randomizing the index
     * layout.
     *
     * @param forceRefresh if {@code true} all involved indices are refreshed
     *   once the documents are indexed. Additionally if {@code true} some
     *   empty dummy documents are may be randomly inserted into the document