Dynamic FieldType inference based on random sampling of documents

Signed-off-by: Rishabh Maurya <rishabhmaurya05@gmail.com>

server/src/main/java/org/opensearch/index/mapper/FieldTypeInference.java

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+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.index.mapper;
+
+import org.apache.lucene.index.IndexReader;
+import org.apache.lucene.index.LeafReaderContext;
+import org.opensearch.common.xcontent.XContentFactory;
+import org.opensearch.common.xcontent.json.JsonXContent;
+import org.opensearch.core.common.bytes.BytesReference;
+import org.opensearch.core.xcontent.XContentBuilder;
+import org.opensearch.search.lookup.SourceLookup;
+
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Random;
+import java.util.Set;
+
+/**
+ * This class performs type inference by analyzing the _source documents. It uses a random sample of documents to infer the field type, similar to dynamic mapping type guessing logic.
+ * Unlike guessing based on the first document, where field could be missing, this method generates a random sample to make a more accurate inference.
+ * This approach is especially useful for handling missing fields, which is common in nested fields within derived fields of object types.
+ *
+ * <p>The sample size should be chosen carefully to ensure a high probability of selecting at least one document where the field is present.
+ * However, it's essential to strike a balance because a large sample size can lead to performance issues since each sample document's _source field is loaded and examined until the field is found.
+ *
+ * <p>Determining the sample size (<var>S</var>) is akin to deciding how many balls to draw from a bin, ensuring a high probability ((<var>&gt;=P</var>)) of drawing at least one green ball (documents with the field) from a mixture of <var>R</var> red balls (documents without the field) and <var>G</var> green balls:
+ * <pre>{@code
+ * P >= 1 - C(R, S) / C(R + G, S)
+ * }</pre>
+ * Here, <var>C()</var> represents the binomial coefficient.
+ * For a high confidence level, we aim for <var>P &gt;= 0.95</var>. For example, with 10^7 documents where the field is present in 2% of them, the sample size <var>S</var> should be around 149 to achieve a probability of 0.95.
+ */
+public class FieldTypeInference {
+    private final IndexReader indexReader;
+    private final String indexName;
+    private final MapperService mapperService;
+    // TODO expose using a index setting
+    private int sampleSize;
+    private static final int DEFAULT_SAMPLE_SIZE = 150;
+    private static final int MAX_SAMPLE_SIZE_ALLOWED = 1000;
+
+    public FieldTypeInference(String indexName, MapperService mapperService, IndexReader indexReader) {
+        this.indexName = indexName;
+        this.mapperService = mapperService;
+        this.indexReader = indexReader;
+        this.sampleSize = DEFAULT_SAMPLE_SIZE;
+    }
+
+    public void setSampleSize(int sampleSize) {
+        this.sampleSize = Math.min(sampleSize, MAX_SAMPLE_SIZE_ALLOWED);
+    }
+
+    public int getSampleSize() {
+        return sampleSize;
+    }
+
+    public Mapper infer(ValueFetcher valueFetcher) throws IOException {
+        RandomSourceValuesGenerator valuesGenerator = new RandomSourceValuesGenerator(sampleSize, indexReader, valueFetcher);
+        Mapper inferredMapper = null;
+        while (inferredMapper == null && valuesGenerator.hasNext()) {
+            List<Object> values = valuesGenerator.next();
+            if (values == null || values.isEmpty()) {
+                continue;
+            }
+            // always use first value in case of multi value field to infer type
+            inferredMapper = inferTypeFromObject(values.get(0));
+        }
+        return inferredMapper;
+    }
+
+    private Mapper inferTypeFromObject(Object o) throws IOException {
+        if (o == null) {
+            return null;
+        }
+        DocumentMapper mapper = mapperService.documentMapper();
+        XContentBuilder builder = XContentFactory.jsonBuilder().startObject().field("field", o).endObject();
+        BytesReference bytesReference = BytesReference.bytes(builder);
+        SourceToParse sourceToParse = new SourceToParse(indexName, "_id", bytesReference, JsonXContent.jsonXContent.mediaType());
+        ParsedDocument parsedDocument = mapper.parse(sourceToParse);
+        Mapping mapping = parsedDocument.dynamicMappingsUpdate();
+        return mapping.root.getMapper("field");
+    }
+
+    private static class RandomSourceValuesGenerator implements Iterator<List<Object>> {
+        private final ValueFetcher valueFetcher;
+        private final IndexReader indexReader;
+        private final SourceLookup sourceLookup;
+        private final int numLeaves;
+        private final int[] docs;
+        private int iter;
+        private int offset;
+        private LeafReaderContext leafReaderContext;
+        private int leaf;
+        private final int MAX_ATTEMPTS_TO_GENERATE_RANDOM_SAMPLES = 10000;
+
+        public RandomSourceValuesGenerator(int sampleSize, IndexReader indexReader, ValueFetcher valueFetcher) {
+            this.valueFetcher = valueFetcher;
+            this.indexReader = indexReader;
+            sampleSize = Math.min(sampleSize, indexReader.numDocs());
+            this.docs = getSortedRandomNum(
+                sampleSize,
+                indexReader.numDocs(),
+                Math.max(sampleSize, MAX_ATTEMPTS_TO_GENERATE_RANDOM_SAMPLES)
+            );
+            this.iter = 0;
+            this.offset = 0;
+            this.leaf = 0;
+            this.numLeaves = indexReader.leaves().size();
+            this.sourceLookup = new SourceLookup();
+            this.leafReaderContext = indexReader.leaves().get(leaf);
+            valueFetcher.setNextReader(leafReaderContext);
+        }
+
+        @Override
+        public boolean hasNext() {
+            return iter < docs.length && leaf < numLeaves;
+        }
+
+        /**
+         * Ensure hasNext() is called before calling next()
+         */
+        @Override
+        public List<Object> next() {
+            int docID = docs[iter] - offset;
+            if (docID >= leafReaderContext.reader().numDocs()) {
+                setNextLeaf();
+                return next();
+            }
+            // deleted docs are getting used to infer type, which should be okay?
+            sourceLookup.setSegmentAndDocument(leafReaderContext, docID);
+            try {
+                iter++;
+                return valueFetcher.fetchValues(sourceLookup);
+            } catch (IOException e) {
+                throw new RuntimeException(e);
+            }
+        }
+
+        private void setNextLeaf() {
+            offset += leafReaderContext.reader().numDocs();
+            leaf++;
+            if (leaf < numLeaves) {
+                leafReaderContext = indexReader.leaves().get(leaf);
+                valueFetcher.setNextReader(leafReaderContext);
+            }
+        }
+
+        private static int[] getSortedRandomNum(int sampleSize, int upperBound, int attempts) {
+            Set<Integer> generatedNumbers = new HashSet<>();
+            Random random = new Random();
+            int itr = 0;
+            while (generatedNumbers.size() < sampleSize && itr++ < attempts) {
+                int randomNumber = random.nextInt(upperBound);
+                generatedNumbers.add(randomNumber);
+            }
+            int[] result = new int[generatedNumbers.size()];
+            int i = 0;
+            for (int number : generatedNumbers) {
+                result[i++] = number;
+            }
+            Arrays.sort(result);
+            return result;
+        }
+    }
+}

server/src/test/java/org/opensearch/index/mapper/FieldTypeInferenceTests.java

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+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.index.mapper;
+
+import org.apache.lucene.document.Document;
+import org.apache.lucene.index.DirectoryReader;
+import org.apache.lucene.index.IndexReader;
+import org.apache.lucene.index.IndexWriter;
+import org.apache.lucene.index.IndexWriterConfig;
+import org.apache.lucene.index.LeafReaderContext;
+import org.apache.lucene.store.Directory;
+import org.opensearch.common.lucene.Lucene;
+import org.opensearch.core.index.Index;
+import org.opensearch.index.query.QueryShardContext;
+import org.opensearch.search.lookup.SourceLookup;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import static org.mockito.Mockito.when;
+
+public class FieldTypeInferenceTests extends MapperServiceTestCase {
+
+    private static final Map<String, List<Object>> documentMap;
+    static {
+        List<Object> listWithNull = new ArrayList<>();
+        listWithNull.add(null);
+        documentMap = new HashMap<>();
+        documentMap.put("text_field", List.of("The quick brown fox jumps over the lazy dog."));
+        documentMap.put("int_field", List.of(789));
+        documentMap.put("float_field", List.of(123.45));
+        documentMap.put("date_field_1", List.of("2024-05-12T15:45:00Z"));
+        documentMap.put("date_field_2", List.of("2024-05-12"));
+        documentMap.put("boolean_field", List.of(true));
+        documentMap.put("null_field", listWithNull);
+        documentMap.put("array_field_int", List.of(100, 200, 300, 400, 500));
+        documentMap.put("array_field_text", List.of("100", "200"));
+        documentMap.put("object_type", List.of(Map.of("foo", Map.of("bar", 10))));
+    }
+
+    public void testJsonSupportedTypes() throws IOException {
+        MapperService mapperService = createMapperService(topMapping(b -> {}));
+        QueryShardContext queryShardContext = createQueryShardContext(mapperService);
+        when(queryShardContext.index()).thenReturn(new Index("test_index", "uuid"));
+        int totalDocs = 10000;
+        int docsPerLeafCount = 1000;
+        int leaves = 0;
+        try (Directory dir = newDirectory()) {
+            IndexWriter iw = new IndexWriter(dir, new IndexWriterConfig(Lucene.STANDARD_ANALYZER));
+            Document d = new Document();
+            for (int i = 0; i < totalDocs; i++) {
+                iw.addDocument(d);
+                if ((i + 1) % docsPerLeafCount == 0) {
+                    iw.commit();
+                    leaves++;
+                }
+            }
+            try (IndexReader reader = DirectoryReader.open(iw)) {
+                iw.close();
+                FieldTypeInference typeInference = new FieldTypeInference("test_index", queryShardContext.getMapperService(), reader);
+                String[] fieldName = { "text_field" };
+                Mapper mapper = typeInference.infer(lookup -> documentMap.get(fieldName[0]));
+                assertEquals("text", mapper.typeName());
+
+                fieldName[0] = "int_field";
+                mapper = typeInference.infer(lookup -> documentMap.get(fieldName[0]));
+                assertEquals("long", mapper.typeName());
+
+                fieldName[0] = "float_field";
+                mapper = typeInference.infer(lookup -> documentMap.get(fieldName[0]));
+                assertEquals("float", mapper.typeName());
+
+                fieldName[0] = "date_field_1";
+                mapper = typeInference.infer(lookup -> documentMap.get(fieldName[0]));
+                assertEquals("date", mapper.typeName());
+
+                fieldName[0] = "date_field_2";
+                mapper = typeInference.infer(lookup -> documentMap.get(fieldName[0]));
+                assertEquals("date", mapper.typeName());
+
+                fieldName[0] = "boolean_field";
+                mapper = typeInference.infer(lookup -> documentMap.get(fieldName[0]));
+                assertEquals("boolean", mapper.typeName());
+
+                fieldName[0] = "array_field_int";
+                mapper = typeInference.infer(lookup -> documentMap.get(fieldName[0]));
+                assertEquals("long", mapper.typeName());
+
+                fieldName[0] = "array_field_text";
+                mapper = typeInference.infer(lookup -> documentMap.get(fieldName[0]));
+                assertEquals("text", mapper.typeName());
+
+                fieldName[0] = "object_type";
+                mapper = typeInference.infer(lookup -> documentMap.get(fieldName[0]));
+                assertEquals("object", mapper.typeName());
+
+                fieldName[0] = "null_field";
+                mapper = typeInference.infer(lookup -> documentMap.get(fieldName[0]));
+                assertNull(mapper);
+
+                // If field is missing ensure that sample docIDs generated for inference are ordered and are in bounds
+                fieldName[0] = "missing_field";
+                List<List<Integer>> docsEvaluated = new ArrayList<>();
+                int[] totalDocsEvaluated = { 0 };
+                typeInference.setSampleSize(50);
+                mapper = typeInference.infer(new ValueFetcher() {
+                    @Override
+                    public List<Object> fetchValues(SourceLookup lookup) throws IOException {
+                        docsEvaluated.get(docsEvaluated.size() - 1).add(lookup.docId());
+                        totalDocsEvaluated[0]++;
+                        return documentMap.get(fieldName[0]);
+                    }
+
+                    @Override
+                    public void setNextReader(LeafReaderContext leafReaderContext) {
+                        docsEvaluated.add(new ArrayList<>());
+                    }
+                });
+                assertNull(mapper);
+                assertEquals(typeInference.getSampleSize(), totalDocsEvaluated[0]);
+                for (List<Integer> docsPerLeaf : docsEvaluated) {
+                    for (int j = 0; j < docsPerLeaf.size() - 1; j++) {
+                        assertTrue(docsPerLeaf.get(j) < docsPerLeaf.get(j + 1));
+                    }
+                    if (!docsPerLeaf.isEmpty()) {
+                        assertTrue(docsPerLeaf.get(0) >= 0 && docsPerLeaf.get(docsPerLeaf.size() - 1) < docsPerLeafCount);
+                    }
+                }
+            }
+        }
+    }
+}