Message Title

the last few days we’ve been digging into an issue where one of our queries send to OpenSearch did not return the expected results. After some digging we found out that when pasting the query into the OpenSearch dashboard we’re getting an error from OpenSearch about “too_many_nested_clauses: Query contains too many nested clauses; maxClauseCount is set to 1024”.

Turning on tracing in of requests in Hibernate Search we can see that OpenSearch is returning the same error here too. However, this error does not seem to be processed by Hibernate Search and the query returns normally just without any results. Here are some relevant parts from the Response:

org.hibernate.search.elasticsearch.request: HSEARCH400093: Executed Elasticsearch HTTP POST request to 'http://opensearch:9200' with path '/my-index1-read,my-index2-read/_search', query parameters {size = 10000, scroll = 30s, track_total_hits = true } and 1 objects in payload in 932ms.Response had status 200 'OK'.Request body:  < {"query": long query....}> .Response body:  
< {
    "_scroll_id": "FG...\u003d\u003d",
    "took": 927,
    "timed_out": false,
    "_shards": {
        "total": 2,
        "successful": 1,
        "skipped": 0,
        "failed": 1,
        "failures": [{
                "shard": 0,
                "index": "my-index1-000001",
                "node": "...",
                "reason": {
                    "type": "too_many_nested_clauses",
                    "reason": "too_many_nested_clauses: Query contains too many nested clauses; maxClauseCount is set to 1024"
                }
            }
        ]
    },
    "hits": {
        "total": {
            "value": 0,
            "relation": "eq"
        },
        "hits": []
    }
}
>

As you can see from the log one of the shards failed executing the query because it’s too complex.

I would have expected Hibernate Search to throw an exception in such case so the system is aware that something went wrong with the query. However browsing the code I could not find any place where the _shards part of the response is actually evaluated.