LUCENE-8810: Honor MaxClausesCount in BooleanQuery (#787)

During Flattening, BooleanQuery will always try to flatten nested clauses during rewrite. However, this can cause the maximum number of clauses to be violated by the new query. This commit disables flattening in the specific case.
apache · Jul 15, 2019 · 8739d5e · 8739d5e
1 parent 4c83fbb
commit 8739d5e
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Showing 2 changed files with 31 additions and 12 deletions.
diff --git a/lucene/core/src/java/org/apache/lucene/search/BooleanQuery.java b/lucene/core/src/java/org/apache/lucene/search/BooleanQuery.java
@@ -481,23 +481,27 @@ public Query rewrite(IndexReader reader) throws IOException {
       BooleanQuery.Builder builder = new BooleanQuery.Builder();
       builder.setMinimumNumberShouldMatch(minimumNumberShouldMatch);
       boolean actuallyRewritten = false;
-      for (BooleanClause clause : clauses) {
-        if (clause.getOccur() == Occur.SHOULD && clause.getQuery() instanceof BooleanQuery) {
-          BooleanQuery innerQuery = (BooleanQuery) clause.getQuery();
-          if (innerQuery.isPureDisjunction()) {
-            actuallyRewritten = true;
-            for (BooleanClause innerClause : innerQuery.clauses()) {
-              builder.add(innerClause);
+      try {
+        for (BooleanClause clause : clauses) {
+          if (clause.getOccur() == Occur.SHOULD && clause.getQuery() instanceof BooleanQuery) {
+            BooleanQuery innerQuery = (BooleanQuery) clause.getQuery();
+            if (innerQuery.isPureDisjunction()) {
+              actuallyRewritten = true;
+              for (BooleanClause innerClause : innerQuery.clauses()) {
+                builder.add(innerClause);
+              }
+            } else {
+              builder.add(clause);
             }
           } else {
             builder.add(clause);
           }
-        } else {
-          builder.add(clause);
         }
-      }
-      if (actuallyRewritten) {
-        return builder.build();
+        if (actuallyRewritten) {
+          return builder.build();
+        }
+      } catch (TooManyClauses exception) {
+        // No-op : Do not flatten when the new query will violate max clause count
       }
     }
 

diff --git a/lucene/core/src/test/org/apache/lucene/search/TestBooleanRewrites.java b/lucene/core/src/test/org/apache/lucene/search/TestBooleanRewrites.java
@@ -598,4 +598,19 @@ public void testDiscardShouldClauses() throws IOException {
     w.close();
     dir.close();
   }
+
+  public void testFlattenInnerDisjunctionsWithMoreThan1024Terms() throws IOException {
+    IndexSearcher searcher = newSearcher(new MultiReader());
+
+    BooleanQuery.Builder builder1024 = new BooleanQuery.Builder();
+    for(int i = 0; i < 1024; i++) {
+      builder1024.add(new TermQuery(new Term("foo", "bar-" + i)), Occur.SHOULD);
+    }
+    Query inner = builder1024.build();
+    Query query = new BooleanQuery.Builder()
+        .add(inner, Occur.SHOULD)
+        .add(new TermQuery(new Term("foo", "baz")), Occur.SHOULD)
+        .build();
+    assertSame(query, searcher.rewrite(query));
+  }
 }