SOLR-17130: edismax MatchAllDocsQuery (*:*) Optimization (#2218)

Author: risdenk

solr/CHANGES.txt

@@ -274,6 +274,8 @@ Optimizations
 
 * SOLR-17801: Use TotalHitCountCollector to collect count when no rows needed (Kevin Risden)
 
+* SOLR-17130: edismax MatchAllDocsQuery (*:*) Optimization (Kevin Risden)
+
 Bug Fixes
 ---------------------
 * SOLR-17629: If SQLHandler failed to open the underlying stream (e.g. Solr returns an error; could be user/syntax problem),

solr/core/src/java/org/apache/solr/search/ExtendedDismaxQParser.java

@@ -186,10 +186,19 @@ public Query parse() throws SyntaxError {
       query.add(f, BooleanClause.Occur.SHOULD);
     }
 
-    //
-    // create a boosted query (scores multiplied by boosts)
-    //
     Query topQuery = QueryUtils.build(query, this);
+
+    // If topQuery is a boolean query, unwrap the boolean query to check if it is just
+    // a MatchAllDocsQuery. Using MatchAllDocsQuery by itself enables later optimizations
+    BooleanQuery topQueryBoolean = (BooleanQuery) topQuery;
+    if (topQueryBoolean.clauses().size() == 1) {
+      Query onlyQuery = topQueryBoolean.clauses().get(0).getQuery();
+      if (onlyQuery instanceof MatchAllDocsQuery) {
+        topQuery = onlyQuery;
+      }
+    }
+
+    // create a boosted query (scores multiplied by boosts)
     List<ValueSource> boosts = getMultiplicativeBoosts();
     if (boosts.size() > 1) {
       ValueSource prod = new ProductFloatFunction(boosts.toArray(new ValueSource[0]));

solr/core/src/test/org/apache/solr/search/TestExtendedDismaxParser.java

@@ -25,6 +25,7 @@
 import static org.hamcrest.Matchers.allOf;
 import static org.hamcrest.Matchers.anyOf;
 import static org.hamcrest.Matchers.containsString;
+import static org.hamcrest.Matchers.isA;
 
 import java.util.Arrays;
 import java.util.HashSet;
@@ -41,6 +42,7 @@
 import org.apache.lucene.search.BoostQuery;
 import org.apache.lucene.search.DisjunctionMaxQuery;
 import org.apache.lucene.search.FuzzyQuery;
+import org.apache.lucene.search.MatchAllDocsQuery;
 import org.apache.lucene.search.Query;
 import org.apache.lucene.search.TermQuery;
 import org.apache.solr.SolrTestCaseJ4;
@@ -143,6 +145,18 @@ public void testSyntax() throws Exception {
     }
   }
 
+  @Test
+  public void testMatchAllDocs() throws Exception {
+    for (String sow : Arrays.asList("true", "false")) {
+      for (String q : Arrays.asList("*:*", "*")) {
+        try (SolrQueryRequest req = req("sow", sow, "qf", "id")) {
+          QParser qParser = QParser.getParser(q, "edismax", req);
+          assertThat(qParser.getQuery(), isA(MatchAllDocsQuery.class));
+        }
+      }
+    }
+  }
+
   public void testTrailingOperators() throws Exception {
     for (String sow : Arrays.asList("true", "false")) {
       // really just test that exceptions aren't thrown by