arangodb · KVS85 · Sep 3, 2021 · Aug 26, 2021 · Aug 26, 2021 · Aug 26, 2021
diff --git a/CHANGELOG b/CHANGELOG
@@ -1,6 +1,9 @@
 v3.8.2 (XXXX-XX-XX)
 -------------------
 
+* SEARCH-238: Improved SortNodes placement optimization in cluster so late
+  materialization could cover more cases.
+
 * Fix rare case of invalid data could be inserted in the ArangoSearch index if
   several clients concurrently inserts data and use custom analyzer with
   non-string return type.

diff --git a/arangod/Aql/OptimizerRules.cpp b/arangod/Aql/OptimizerRules.cpp
@@ -4870,6 +4870,7 @@ void arangodb::aql::distributeSortToClusterRule(Optimizer* opt,
                                                 OptimizerRule const& rule) {
   ::arangodb::containers::SmallVector<ExecutionNode*>::allocator_type::arena_type a;
   ::arangodb::containers::SmallVector<ExecutionNode*> nodes{a};
+  VarSet usedBySort;
   plan->findNodesOfType(nodes, EN::GATHER, true);
 
   bool modified = false;
@@ -4931,14 +4932,37 @@ void arangodb::aql::distributeSortToClusterRule(Optimizer* opt,
 
         case EN::SORT: {
           auto thisSortNode = ExecutionNode::castTo<SortNode*>(inspectNode);
-
+          usedBySort.clear();
+          thisSortNode->getVariablesUsedHere(usedBySort);
           // remember our cursor...
           parents = inspectNode->getParents();
           // then unlink the filter/calculator from the plan
           plan->unlinkNode(inspectNode);
           // and re-insert into plan in front of the remoteNode
           if (thisSortNode->_reinsertInCluster) {
-            plan->insertDependency(rn, inspectNode);
+            // let's look for the best place for that SORT.
+            // We could skip over several calculations if
+            // they are not needed for our sort. So we could calculate
+            // more lazily and even make late materialization possible
+            ExecutionNode* insertPoint = rn;
+            auto current  = insertPoint->getFirstDependency();
+            while (current != nullptr &&
+                   current->getType() == EN::CALCULATION) {
+              auto nn = ExecutionNode::castTo<CalculationNode*>(current);
+              if (!nn->expression()->isDeterministic()) {
+                // let's not touch non-deterministic calculation
+                // as results may depend on calls count and sort could change this
+                break;
+              }
+              auto variable = nn->outVariable();
+              if (usedBySort.find(variable) == usedBySort.end()) {
+                insertPoint = current;
+              } else {
+                break;  // first node used by sort. We should stop here.
+              }
+              current = current->getFirstDependency();
+            }
+            plan->insertDependency(insertPoint, inspectNode);
           }
 
           gatherNode->elements(thisSortNode->elements());

diff --git a/tests/js/server/aql/aql-optimizer-rule-late-document-materialization-arangosearch.inc b/tests/js/server/aql/aql-optimizer-rule-late-document-materialization-arangosearch.inc
@@ -380,6 +380,34 @@
         });
         assertEqual(0, expected.size);
       },
+      testConstrainedSortOnDbServer() {
+        let query = "FOR d IN " + vn  + " SEARCH d.value > 9 SORT BM25(d) LIMIT 10 RETURN {key: d._key, value: d.value}";
+        let plan = AQL_EXPLAIN(query).plan;
+        assertNotEqual(-1, plan.rules.indexOf(ruleName));
+        let materializeNodeFound = false;
+        let nodeDependency = null;
+        plan.nodes.forEach(function(node) {
+          if( node.type === "MaterializeNode") {
+            assertFalse(materializeNodeFound);
+            // FIXME: temporary relaxed assertion
+            // We need to fix node placement in oneshard mode
+            // first. And than we indeed will get expected node placement
+            // assertEqual(nodeDependency.type, isCluster ? "SortNode" : "LimitNode");
+            assertTrue(nodeDependency.type === "SortNode" ||  nodeDependency.type === "LimitNode");
+            materializeNodeFound = true;
+          }
+          nodeDependency = node;
+        });
+        assertTrue(materializeNodeFound);
+        let result = AQL_EXECUTE(query);
+        assertEqual(4, result.json.length);
+        let expected = new Set(['c_0', 'c_1', 'c_2', 'c_3']);
+        result.json.forEach(function(doc) {
+          assertTrue(expected.has(doc.key));
+          expected.delete(doc.key);
+        });
+        assertEqual(0, expected.size);
+      }
     };
   };
 }());

diff --git a/tests/js/server/aql/aql-optimizer-rule-late-document-materialization.js b/tests/js/server/aql/aql-optimizer-rule-late-document-materialization.js
@@ -607,6 +607,31 @@ function lateDocumentMaterializationRuleTestSuite () {
       let result = AQL_EXECUTE(query);
       assertEqual(1, result.json.length);
       assertEqual(result.json[0]._key, 'c0');
+    },
    testConstrainedSortOnDbServer() {
+      let query = "FOR d IN " + prefixIndexCollectionName  + " FILTER d.obj.b == {sb: 'b_val_0'} " +
+                  "SORT d.obj.b LIMIT 10 RETURN {key: d._key, value:  d.some_value_from_doc}";
+      let plan = AQL_EXPLAIN(query).plan;
+      assertNotEqual(-1, plan.rules.indexOf(ruleName));
+      let materializeNodeFound = false;
+      let nodeDependency = null;
+      plan.nodes.forEach(function(node) {
+        if( node.type === "MaterializeNode") {
+          assertFalse(materializeNodeFound);
+          assertEqual(nodeDependency.type, isCluster ? "SortNode" : "LimitNode");
+          materializeNodeFound = true;
+        }
+        nodeDependency = node;
+      });
+      assertTrue(materializeNodeFound);
+      let result = AQL_EXECUTE(query);
+      assertEqual(1, result.json.length);
+      let expected = new Set(['c0']);
+      result.json.forEach(function(doc) {
+        assertTrue(expected.has(doc.key));
+        expected.delete(doc.key);
+      });
+      assertEqual(0, expected.size);
     }
   };
 }

diff --git a/tests/js/server/aql/aql-queries-optimizer-limit-cluster.js b/tests/js/server/aql/aql-queries-optimizer-limit-cluster.js
@@ -601,7 +601,17 @@ function ahuacatlQueryOptimizerLimitTestSuite () {
       var actual = getQueryResults(query);
       assertEqual(0, actual.length);
 
-      assertEqual([ "SingletonNode", "EnumerateCollectionNode", "CalculationNode", "CalculationNode", "SortNode", "RemoteNode", "GatherNode", "LimitNode", "FilterNode", "ReturnNode" ], explain(query));
+      assertEqual([ "SingletonNode", "EnumerateCollectionNode", "CalculationNode", "SortNode", "CalculationNode",
+	                "RemoteNode", "GatherNode", "LimitNode", "FilterNode", "ReturnNode" ], explain(query));
+    },
+    testLimitFullCollectionSort3_DoubleCalculation : function () {
+      var query = "FOR c IN " + cn + " SORT c.value LIMIT 0, 10 FILTER c.value >= 20 && c.value < 30 RETURN c.value2";
+
+      var actual = getQueryResults(query);
+      assertEqual(0, actual.length);
+
+      assertEqual([ "SingletonNode", "EnumerateCollectionNode", "CalculationNode", "SortNode", "CalculationNode",
+	                "CalculationNode", "RemoteNode", "GatherNode", "LimitNode", "FilterNode", "ReturnNode" ], explain(query));
     },
 
 ////////////////////////////////////////////////////////////////////////////////