Add custom MoreLikeThis with sharding support

src/main/java/it/cavallium/dbengine/database/LLUtils.java

@@ -10,13 +10,13 @@ import io.net5.buffer.api.Send;
 import io.net5.util.IllegalReferenceCountException;
 import io.net5.util.internal.PlatformDependent;
 import it.cavallium.dbengine.database.collections.DatabaseStage;
-import it.cavallium.dbengine.database.disk.LLIndexContext;
 import it.cavallium.dbengine.database.disk.LLIndexSearcher;
 import it.cavallium.dbengine.database.disk.LLLocalLuceneIndex;
 import it.cavallium.dbengine.database.disk.MemorySegmentUtils;
 import it.cavallium.dbengine.database.serialization.SerializationException;
 import it.cavallium.dbengine.database.serialization.SerializationFunction;
 import it.cavallium.dbengine.lucene.RandomSortField;
+import it.cavallium.dbengine.lucene.analyzer.WordAnalyzer;
 import it.cavallium.dbengine.lucene.searcher.LocalQueryParams;
 import java.nio.ByteBuffer;
 import java.nio.charset.Charset;
@@ -33,6 +33,7 @@ import java.util.concurrent.Callable;
 import java.util.concurrent.atomic.AtomicLong;
 import java.util.function.Function;
 import java.util.function.ToIntFunction;
+import org.apache.lucene.analysis.Analyzer;
 import org.apache.lucene.document.Document;
 import org.apache.lucene.document.Field;
 import org.apache.lucene.document.FloatPoint;
@@ -41,9 +42,10 @@ import org.apache.lucene.document.LongPoint;
 import org.apache.lucene.document.SortedNumericDocValuesField;
 import org.apache.lucene.document.StringField;
 import org.apache.lucene.document.TextField;
+import org.apache.lucene.index.IndexReader;
 import org.apache.lucene.index.IndexableField;
 import org.apache.lucene.index.Term;
-import org.apache.lucene.queries.mlt.MoreLikeThis;
+import it.cavallium.dbengine.lucene.mlt.MultiMoreLikeThis;
 import org.apache.lucene.search.BooleanClause.Occur;
 import org.apache.lucene.search.BooleanQuery;
 import org.apache.lucene.search.ConstantScoreQuery;
@@ -51,10 +53,11 @@ import org.apache.lucene.search.MatchAllDocsQuery;
 import org.apache.lucene.search.MatchNoDocsQuery;
 import org.apache.lucene.search.Query;
 import org.apache.lucene.search.ScoreMode;
-import org.apache.lucene.search.SearcherManager;
 import org.apache.lucene.search.Sort;
 import org.apache.lucene.search.SortField;
 import org.apache.lucene.search.SortedNumericSortField;
+import org.apache.lucene.search.similarities.ClassicSimilarity;
+import org.apache.lucene.search.similarities.Similarity;
 import org.apache.lucene.search.similarities.TFIDFSimilarity;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
@@ -397,9 +400,11 @@ public class LLUtils {
 	}
 
 	public static Mono<LocalQueryParams> getMoreLikeThisQuery(
-			LLIndexSearcher indexSearcher,
+			List<LLIndexSearcher> indexSearchers,
 			@Nullable LLSnapshot snapshot,
 			LocalQueryParams localQueryParams,
+			Analyzer analyzer,
+			Similarity similarity,
 			Flux<Tuple2<String, Set<String>>> mltDocumentFieldsFlux) {
 		Query luceneAdditionalQuery;
 		try {
@@ -409,33 +414,38 @@ public class LLUtils {
 		}
 		return mltDocumentFieldsFlux
 				.collectMap(Tuple2::getT1, Tuple2::getT2, HashMap::new)
-				.flatMap(mltDocumentFields -> {
+				.flatMap(mltDocumentFields -> Mono.fromCallable(() -> {
 					mltDocumentFields.entrySet().removeIf(entry -> entry.getValue().isEmpty());
 					if (mltDocumentFields.isEmpty()) {
-						return Mono.just(new LocalQueryParams(new MatchNoDocsQuery(),
+						return new LocalQueryParams(new MatchNoDocsQuery(),
 								localQueryParams.offset(),
 								localQueryParams.limit(),
 								localQueryParams.minCompetitiveScore(),
 								localQueryParams.sort(),
 								localQueryParams.scoreMode()
-						));
+						);
 					}
-					new IndexSearcher
-					return indexSearcher.getIndexSearcher().search(snapshot, indexSearcher -> Mono.fromCallable(() -> {
-						var mlt = new MoreLikeThis(indexSearcher.getIndexReader());
-						mlt.setAnalyzer(llLocalLuceneIndex.indexWriter.getAnalyzer());
+					MultiMoreLikeThis mlt;
+					if (indexSearchers.size() == 1) {
+						mlt = new MultiMoreLikeThis(indexSearchers.get(0).getIndexReader(), null);
+					} else {
+						IndexReader[] indexReaders = new IndexReader[indexSearchers.size()];
+						for (int i = 0, size = indexSearchers.size(); i < size; i++) {
+							indexReaders[i] = indexSearchers.get(i).getIndexReader();
+						}
+						mlt = new MultiMoreLikeThis(indexReaders, null);
+					}
+					mlt.setAnalyzer(analyzer);
 					mlt.setFieldNames(mltDocumentFields.keySet().toArray(String[]::new));
 					mlt.setMinTermFreq(1);
 					mlt.setMinDocFreq(3);
 					mlt.setMaxDocFreqPct(20);
 					mlt.setBoost(localQueryParams.scoreMode().needsScores());
 					mlt.setStopWords(EnglishItalianStopFilter.getStopWordsString());
-						var similarity = llLocalLuceneIndex.getSimilarity();
-						if (similarity instanceof TFIDFSimilarity) {
-							mlt.setSimilarity((TFIDFSimilarity) similarity);
+					if (similarity instanceof TFIDFSimilarity tfidfSimilarity) {
+						mlt.setSimilarity(tfidfSimilarity);
 					} else {
-							LLLocalLuceneIndex.logger.trace(MARKER_ROCKSDB, "Using an unsupported similarity algorithm for MoreLikeThis:"
-									+ " {}. You must use a similarity instance based on TFIDFSimilarity!", similarity);
+						mlt.setSimilarity(new ClassicSimilarity());
 					}
 
 					// Get the reference docId and apply it to MoreLikeThis, to generate the query
@@ -451,17 +461,14 @@ public class LLUtils {
 						luceneQuery = mltQuery;
 					}
 
-						return luceneQuery;
-					})
-					.subscribeOn(Schedulers.boundedElastic())
-					.map(luceneQuery -> new LocalQueryParams(luceneQuery,
+					return new LocalQueryParams(luceneQuery,
 							localQueryParams.offset(),
 							localQueryParams.limit(),
 							localQueryParams.minCompetitiveScore(),
 							localQueryParams.sort(),
 							localQueryParams.scoreMode()
-					)));
-				});
+					);
+				}).subscribeOn(Schedulers.boundedElastic()));
 	}
 
 	public static record DirectBuffer(@NotNull Send<Buffer> buffer, @NotNull ByteBuffer byteBuffer) {}