Fix results ordering

src/main/java/it/cavallium/dbengine/lucene/LuceneUtils.java

@@ -30,7 +30,9 @@ import java.util.HashMap;
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.NoSuchElementException;
+import java.util.Objects;
 import java.util.Set;
+import java.util.function.Function;
 import java.util.stream.Collectors;
 import org.apache.lucene.analysis.Analyzer;
 import org.apache.lucene.analysis.LowerCaseFilter;
@@ -349,32 +351,49 @@ public class LuceneUtils {
 	public static Flux<LLKeyScore> convertHits(ScoreDoc[] hits,
 			IndexSearchers indexSearchers,
 			String keyFieldName,
-			Scheduler scheduler) {
+			Scheduler scheduler,
+			boolean preserveOrder) {
 
 		return Flux
 				.fromArray(hits)
-				.parallel()
+				.transform(hitsFlux -> {
-				.runOn(scheduler)
+					if (preserveOrder) {
-				.map(hit -> {
+						return hitsFlux
-					int shardDocId = hit.doc;
+								.publishOn(scheduler)
-					int shardIndex = hit.shardIndex;
+								.mapNotNull(hit -> mapHitBlocking(hit, indexSearchers, keyFieldName));
-					float score = hit.score;
+					} else {
-					var indexSearcher = indexSearchers.shard(shardIndex);
+						return hitsFlux
-					try {
+								.parallel()
-						//noinspection BlockingMethodInNonBlockingContext
+								.runOn(scheduler)
-						String collectedDoc = keyOfTopDoc(shardDocId, indexSearcher.getIndexReader(), keyFieldName);
+								.map(hit -> {
-						return new LLKeyScore(shardDocId, score, Mono.just(collectedDoc));
+									var result = mapHitBlocking(hit, indexSearchers, keyFieldName);
-					} catch (NoSuchElementException ex) {
+									// The "else" value is an errored key score, to filter out next
-						logger.debug("Error: document " + shardDocId + " key is not present!");
+									return Objects.requireNonNullElseGet(result, () -> new LLKeyScore(-1, -1, Mono.empty()));
-						// Errored key score, to filter out next
+								})
-						return new LLKeyScore(-1, -1, Mono.empty());
+								.sequential()
-					} catch (Exception ex) {
+								// Filter out the errored key scores
-						return new LLKeyScore(shardDocId, score, Mono.error(ex));
+								.filter(ks -> !(ks.docId() == -1 && ks.score() == -1));
 					}
-				})
+				});
-				// Filter out the errored key scores
+	}
-				.filter(ks -> !(ks.docId() == -1 && ks.score() == -1))
+
-				.sequential();
+	@Nullable
+	private static LLKeyScore mapHitBlocking(ScoreDoc hit,
+			IndexSearchers indexSearchers,
+			String keyFieldName) {
+		int shardDocId = hit.doc;
+		int shardIndex = hit.shardIndex;
+		float score = hit.score;
+		var indexSearcher = indexSearchers.shard(shardIndex);
+		try {
+			String collectedDoc = keyOfTopDoc(shardDocId, indexSearcher.getIndexReader(), keyFieldName);
+			return new LLKeyScore(shardDocId, score, Mono.just(collectedDoc));
+		} catch (NoSuchElementException ex) {
+			logger.debug("Error: document " + shardDocId + " key is not present!");
+			return null;
+		} catch (Exception ex) {
+			return new LLKeyScore(shardDocId, score, Mono.error(ex));
+		}
 	}
 
 	/**

src/main/java/it/cavallium/dbengine/lucene/searcher/ScoredSimpleLuceneShardSearcher.java

@@ -81,7 +81,7 @@ class ScoredSimpleLuceneShardSearcher implements LuceneShardSearcher {
 						indexSearchers = IndexSearchers.of(indexSearchersArray);
 					}
 					Flux<LLKeyScore> firstPageHits = LuceneUtils
-							.convertHits(result.scoreDocs, indexSearchers, keyFieldName, scheduler);
+							.convertHits(result.scoreDocs, indexSearchers, keyFieldName, scheduler, true);
 
 					Flux<LLKeyScore> nextHits = Flux.defer(() -> {
 						if (paginationInfo.forceSinglePage()
@@ -136,7 +136,7 @@ class ScoredSimpleLuceneShardSearcher implements LuceneShardSearcher {
 								)
 								.subscribeOn(scheduler)
 								.flatMapSequential(topFieldDoc -> LuceneUtils
-										.convertHits(topFieldDoc.scoreDocs, indexSearchers, keyFieldName, scheduler)
+										.convertHits(topFieldDoc.scoreDocs, indexSearchers, keyFieldName, scheduler, true)
 								);
 					});
 

src/main/java/it/cavallium/dbengine/lucene/searcher/SimpleLuceneLocalSearcher.java

@@ -53,7 +53,8 @@ public class SimpleLuceneLocalSearcher implements LuceneLocalSearcher {
 									firstPageTopDocs.scoreDocs,
 									IndexSearchers.unsharded(indexSearcher),
 									keyFieldName,
-									scheduler
+									scheduler,
+									true
 							)
 							.take(queryParams.limit(), true);
 
@@ -96,7 +97,7 @@ public class SimpleLuceneLocalSearcher implements LuceneLocalSearcher {
 									)
 									.subscribeOn(scheduler)
 									.flatMapSequential(topFieldDoc -> LuceneUtils
-											.convertHits(topFieldDoc.scoreDocs, IndexSearchers.unsharded(indexSearcher), keyFieldName, scheduler)
+											.convertHits(topFieldDoc.scoreDocs, IndexSearchers.unsharded(indexSearcher), keyFieldName, scheduler, true)
 									);
 						});
 					}

src/main/java/it/cavallium/dbengine/lucene/searcher/UnscoredPagedLuceneShardSearcher.java

@@ -73,7 +73,7 @@ class UnscoredPagedLuceneShardSearcher implements LuceneShardSearcher {
 						indexSearchers = IndexSearchers.of(indexSearchersArray);
 					}
 					Flux<LLKeyScore> firstPageHits = LuceneUtils
-							.convertHits(result.scoreDocs, indexSearchers, keyFieldName, scheduler);
+							.convertHits(result.scoreDocs, indexSearchers, keyFieldName, scheduler, false);
 
 					Flux<LLKeyScore> nextHits = Flux.defer(() -> {
 						if (paginationInfo.forceSinglePage() || paginationInfo.totalLimit() - paginationInfo.firstPageLimit() <= 0) {
@@ -124,7 +124,7 @@ class UnscoredPagedLuceneShardSearcher implements LuceneShardSearcher {
 								)
 								.subscribeOn(scheduler)
 								.flatMapSequential(topFieldDoc -> LuceneUtils
-										.convertHits(topFieldDoc.scoreDocs, indexSearchers, keyFieldName, scheduler)
+										.convertHits(topFieldDoc.scoreDocs, indexSearchers, keyFieldName, scheduler, false)
 								);
 					});
 

src/main/java/it/cavallium/dbengine/lucene/searcher/UnscoredUnsortedContinuousLuceneMultiSearcher.java

@@ -148,7 +148,8 @@ public class UnscoredUnsortedContinuousLuceneMultiSearcher implements LuceneMult
 												.flatMap(scoreDocs -> LuceneUtils.convertHits(scoreDocs.toArray(ScoreDoc[]::new),
 														indexSearchers,
 														keyFieldName,
-														scheduler
+														scheduler,
+														false
 												));
 
 										return new LuceneSearchResult(1, resultsFlux, release);