Random_score query brought down ES 5.5 cluster

[vglazkov (Vitlalii Glazkov)]

This question is similar to this one:

This query brought down my cluster :{"query": {"function_score": {"query": {"match_all":{}}, "random_score": {"seed": 123456}}}}

Hi, I like to share my experience and in the same time hope I can get some tips. The query was run against an index with about 700 million documents. Two things happens, The node run this query crashed. It is the node configured not to proccess data. The data nodes start crazy on GC. eventually old generation gc cannot reduce the heep usage and the nodes becomes unresponsive. in some cases. OLD generation gc even increased size of the heap: 2014-12-20 07:21:03,370][WARN ][mon…

The difference between the tickets is that I have intentionally specified size parameter. Index contains little more than 8 billions of documents. Here's my query:

{
    "version": true,
	"size": 5000,
	"query": {
		"function_score": {
			"query": {
				"bool": {
					"must": {
						"match_all": {}
					},
					"filter": {
						"range": {
							"updated": {
								"lte": "1556015239000"
							}
						}
					}
				}
			},
			"functions": [{
				"random_score": {
					"seed": 0
				}
			}]
		}
	}
}

My question is why did this happen?

[spinscale (Alexander Reelsen)]

size: 5000 only returns 5000 documents in the search response (which also is a lot and you should consider using scroll searches). However in order to get those 5000 documents the script score query needs to be executed against every hit that matches the query in the function score, which may be far more than those 5k.