# Function\_score is so slow . how can i slove it?

**URL:** <https://discuss.elastic.co/t/function-score-is-so-slow-how-can-i-slove-it/242636>\
**Category:** Elasticsearch\
**Created:** [July 26, 2020, 7:40am UTC](https://discuss.elastic.co/t/function-score-is-so-slow-how-can-i-slove-it/242636 "2020-07-26T07:40:18Z")\
**Posts on this page:** 8\
**Page:** 1

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**Author:** ![liutao053877](https://avatars.discourse-cdn.com/v4/letter/l/e480ec/32.png) [@liutao053877](https://discuss.elastic.co/u/liutao053877)\
**Post date:** [July 26, 2020, 7:40am UTC](https://discuss.elastic.co/t/function-score-is-so-slow-how-can-i-slove-it/242636/1 "2020-07-26T07:40:18Z")

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just like this . : [Simple Function Score Query Shows Very Poor Performance](https://discuss.elastic.co/t/simple-function-score-query-shows-very-poor-performance/274)

I use the version es 6.8. I write a rescore plugin in java and the speed is so slow .  
I rescore need to fetch one field to calculate the score like bm25.

I find it is slow because of the code like :  
String sentence=(String)leafLookup.source().get("fieldname");

when I replace the code as a constant string is it faster.how can i solve it ?

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<div class="post-metadata">

**Author:** ![liutao053877](https://avatars.discourse-cdn.com/v4/letter/l/e480ec/32.png) [@liutao053877](https://discuss.elastic.co/u/liutao053877)\
**Post date:** [July 26, 2020, 7:43am UTC](https://discuss.elastic.co/t/function-score-is-so-slow-how-can-i-slove-it/242636/2 "2020-07-26T07:43:01Z")

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The key code here,very simple:

package com.esplugin.demo;

import org.apache.lucene.index.LeafReaderContext;  
import org.apache.lucene.index.PostingsEnum;  
import org.apache.lucene.index.Term;  
import org.elasticsearch.common.settings.Settings;  
import org.elasticsearch.plugins.Plugin;  
import org.elasticsearch.plugins.ScriptPlugin;  
import org.elasticsearch.script.ScoreScript;  
import org.elasticsearch.script.ScoreScript.LeafFactory;  
import org.elasticsearch.script.ScriptContext;  
import org.elasticsearch.script.ScriptEngine;  
import org.elasticsearch.search.lookup.SearchLookup;

import java.io.IOException;  
import java.io.UncheckedIOException;  
import java.util.Collection;  
import java.util.Map;  
import java.util.Set;  
import org.apache.logging.log4j.LogManager;  
import org.apache.logging.log4j.Logger;  
import org.apache.lucene.search.Scorer;

import com.pingan.llx.es.util.MyBM25FSimilarity;

public class MyScriptEngine implements ScriptEngine {  
private final static Logger logger = LogManager.getLogger(MyRankPlugin.class);  
public static String type="MyRankPlugin";  
@Override  
public String getType() {  
return type;  
}

```
@Override
public <T> T compile(String scriptName, String scriptSource,
                     ScriptContext<T> context, Map<String, String> params) {
    if (context.equals(ScoreScript.CONTEXT) == false) {
        throw new IllegalArgumentException(getType()
                + " scripts cannot be used for context ["
                + context.name + "]");
    }
    // we use the script "source" as the script identifier
    if (type.equals(scriptSource)) {
        ScoreScript.Factory factory = PureDfLeafFactory::new;
        return context.factoryClazz.cast(factory);
    }
    throw new IllegalArgumentException("Unknown script name "
            + scriptSource);
}

@Override
public void close() {
    // optionally close resources
}

private static class PureDfLeafFactory implements LeafFactory {
    private final Map<String, Object> params;
    private final SearchLookup lookup;
    private MyBM25FSimilarity myBM25=new MyBM25FSimilarity();

    private PureDfLeafFactory(
            Map<String, Object> params, SearchLookup lookup) {
        if (params.containsKey("query") == false) {
            throw new IllegalArgumentException(
                    "Missing parameter [query]");
        }
        if (params.containsKey("f") == false) {
            throw new IllegalArgumentException(
                    "Missing parameter [f]");
        }
        this.params = params;
        this.lookup = lookup;
    }

    @Override
    public boolean needs_score() {
        return false; // Return true if the script needs the score
    }

    @Override
    public ScoreScript newInstance(LeafReaderContext context)
            throws IOException {
            /*
             * the field and/or term don't exist in this segment,
             * so always return 0
             */
            return new ScoreScript(params, lookup, context) {

                @Override
                public double execute() {
                    try {

                        String query = params.get("query").toString();
                        String f=params.get("f").toString();
                        //logger.info("this is query value2 : {} {}", query,f);

                        String sentence = (String) lookup.source().get(f);
                        //logger.info("this is sentence : {}", sentence);

                        double score = myBM25.score(query, sentence);
                        //logger.info("this is query value2 : {},{},{},{}", query,sentence,String.valueOf(score),String.valueOf(rawScore));
                        //this.setScorer(score);
                        return score;
                    }catch(Exception e){
                        e.printStackTrace();
                    }
                    return 0;
                }
            };
        }
    }

```

}

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<div class="post-metadata">

**Author:** ![liutao053877](https://avatars.discourse-cdn.com/v4/letter/l/e480ec/32.png) [@liutao053877](https://discuss.elastic.co/u/liutao053877)\
**Post date:** [July 26, 2020, 7:44am UTC](https://discuss.elastic.co/t/function-score-is-so-slow-how-can-i-slove-it/242636/3 "2020-07-26T07:44:21Z")

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about 7-10 times slower than without a Function Score Script

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<div class="post-metadata">

**Author:** ![Christian\_Dahlqvist](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/christian_dahlqvist/32/4617_2.png) [@Christian\_Dahlqvist](https://discuss.elastic.co/u/Christian_Dahlqvist)\
**Post date:** [July 26, 2020, 8:24am UTC](https://discuss.elastic.co/t/function-score-is-so-slow-how-can-i-slove-it/242636/4 "2020-07-26T08:24:52Z")

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Using data from source means the document need to be loaded, which will take longer.  
Lower performance us therefore IMHO expected.

How long is the field?

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<div class="post-metadata">

**Author:** ![liutao053877](https://avatars.discourse-cdn.com/v4/letter/l/e480ec/32.png) [@liutao053877](https://discuss.elastic.co/u/liutao053877)\
**Post date:** [July 26, 2020, 9:12am UTC](https://discuss.elastic.co/t/function-score-is-so-slow-how-can-i-slove-it/242636/5 "2020-07-26T09:12:09Z")

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the field is short text no more than 50 chars.

IMHO? how can i use the api ?

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<div class="post-metadata">

**Author:** ![Christian\_Dahlqvist](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/christian_dahlqvist/32/4617_2.png) [@Christian\_Dahlqvist](https://discuss.elastic.co/u/Christian_Dahlqvist)\
**Post date:** [July 26, 2020, 10:06am UTC](https://discuss.elastic.co/t/function-score-is-so-slow-how-can-i-slove-it/242636/6 "2020-07-26T10:06:27Z")

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Have you got the field indexed as keyword so it would be available as a doc value?

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<div class="post-metadata">

**Author:** ![liutao053877](https://avatars.discourse-cdn.com/v4/letter/l/e480ec/32.png) [@liutao053877](https://discuss.elastic.co/u/liutao053877)\
**Post date:** [July 26, 2020, 11:03am UTC](https://discuss.elastic.co/t/function-score-is-so-slow-how-can-i-slove-it/242636/7 "2020-07-26T11:03:09Z")

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No the field I got is indexed not as keyword but seg with default segment.  
I tried String a=((ScriptDocValues.Strings)this.getDoc().get(f)).getValue() ; to get the field data but not sucess.

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<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [August 23, 2020, 11:14am UTC](https://discuss.elastic.co/t/function-score-is-so-slow-how-can-i-slove-it/242636/8 "2020-08-23T11:14:40Z")

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