make use of projections if the projected data is used by an IndexNode's condition (#8001)

arangod/RocksDBEngine/RocksDBOptimizerRules.cpp

@@ -91,7 +91,7 @@ void RocksDBOptimizerRules::reduceExtractionToProjectionRule(
     ExecutionNode* current = n->getFirstParent();
     while (current != nullptr) {
       bool doRegularCheck = false;
-
+    
       if (current->getType() == EN::REMOVE) {
         RemoveNode const* removeNode = ExecutionNode::castTo<RemoveNode const*>(current);
         if (removeNode->inVariable() == v) {
@@ -145,6 +145,22 @@ void RocksDBOptimizerRules::reduceExtractionToProjectionRule(
             attributes.emplace(it.attributePath[0]);
           }
         }
+      } else if (current->getType() == EN::INDEX) {
+        Condition const* condition = ExecutionNode::castTo<IndexNode const*>(current)->condition();
+
+        if (condition != nullptr && condition->root() != nullptr) {
+          AstNode const* node = condition->root();
+          vars.clear();
+          current->getVariablesUsedHere(vars);
+
+          if (vars.find(v) != vars.end()) {
+            if (!Ast::getReferencedAttributes(node, v, attributes)) {
+              stop = true;
+              break;
+            }
+            optimize = true;
+          }
+        }
       } else {
         // all other node types mandate a check
         doRegularCheck = true;
@@ -170,12 +186,8 @@ void RocksDBOptimizerRules::reduceExtractionToProjectionRule(
 
     // projections are currently limited (arbitrarily to 5 attributes)
     if (optimize && !stop && !attributes.empty() && attributes.size() <= 5) {
-      std::vector<std::string> r;
-      for (auto& it : attributes) {
-        r.emplace_back(std::move(it));
-      }
       // store projections in DocumentProducingNode
-      e->projections(std::move(r));
+      e->projections(std::move(attributes));
 
       if (n->getType() == ExecutionNode::INDEX) {
         // need to update _indexCoversProjections value in an IndexNode

arangod/RocksDBEngine/RocksDBPrimaryIndex.cpp

@@ -288,7 +288,6 @@ bool RocksDBPrimaryIndexInIterator::nextCovering(DocumentCallback const& cb, siz
   }
 
   while (limit > 0) {
-    // TODO: prevent copying of the value into result, as we don't need it here!
     LocalDocumentId documentId = _index->lookupKey(_trx, StringRef(*_iterator));
     if (documentId.isSet()) {
       cb(documentId, *_iterator);

tests/js/server/aql/aql-optimizer-rule-reduce-extraction-to-projection-rocksdb.js

@@ -228,15 +228,36 @@ function optimizerRuleTestSuite () {
         result = AQL_EXECUTE(query[0], { "@cn" : cn });
         assertEqual(query[1], result.json);
       });
+    },
+
+    testJoin : function () {
+      c.ensureIndex({ type: "skiplist", fields: ["value"] });
+
+      let queries = [
+        "FOR doc1 IN @@cn FOR doc2 IN @@cn FILTER doc1.value == doc2._key RETURN [doc1._key, doc2._key]",
+        "FOR doc1 IN @@cn FOR doc2 IN @@cn FILTER doc1.value == doc2._key RETURN [doc1.value, doc2._key]",
+      ];
+      
+      queries.forEach(function(query) {
+        let result = AQL_EXPLAIN(query, { "@cn" : cn });
+        assertNotEqual(-1, result.plan.rules.indexOf(ruleName), query);
+      
+        let found = 0;
+        result.plan.nodes.filter(function(node) { 
+          return node.type === 'IndexNode' || node.type === 'EnumerateCollectionNode';
+        }).forEach(function(node) {
+          assertNotEqual([], node.projections);
+          ++found;
+        });
+
+        assertEqual(2, found);
+      });
     }
     
   };
 }
 
-////////////////////////////////////////////////////////////////////////////////
 /// @brief executes the test suite
-////////////////////////////////////////////////////////////////////////////////
-
 jsunity.run(optimizerRuleTestSuite);
 
 return jsunity.done();