Implementation outline of MultiDependencySingleRowFetcher::skipSome for subqueryDepth > 0

arangod/Aql/MultiDependencySingleRowFetcher.cpp

@@ -34,7 +34,7 @@ MultiDependencySingleRowFetcher::DependencyInfo::DependencyInfo()
 
 MultiDependencySingleRowFetcher::MultiDependencySingleRowFetcher(
     DependencyProxy<BlockPassthrough::Disable>& executionBlock)
-    : _dependencyProxy(&executionBlock) {}
+    : _dependencyProxy{&executionBlock}, _dependencyInfos{}, _nextSkipDependencyIndex{0} {}
 
 std::pair<ExecutionState, SharedAqlItemBlockPtr> MultiDependencySingleRowFetcher::fetchBlockForDependency(
     size_t dependency, size_t atMost) {
@@ -148,7 +148,7 @@ std::pair<ExecutionState, ShadowAqlItemRow> MultiDependencySingleRowFetcher::fet
 }
 
 MultiDependencySingleRowFetcher::MultiDependencySingleRowFetcher()
-    : _dependencyProxy(nullptr) {}
+    : _dependencyProxy{nullptr}, _dependencyInfos{}, _nextSkipDependencyIndex{0} {}
 
 RegisterId MultiDependencySingleRowFetcher::getNrInputRegisters() const {
   return _dependencyProxy->getNrInputRegisters();
@@ -229,7 +229,7 @@ std::pair<ExecutionState, InputAqlItemRow> MultiDependencySingleRowFetcher::fetc
 }
 
 std::pair<ExecutionState, size_t> MultiDependencySingleRowFetcher::skipRowsForDependency(
-    size_t const dependency, size_t const atMost, size_t const subqueryDepth) {
+    size_t const dependency, size_t const atMost) {
   TRI_ASSERT(dependency < _dependencyInfos.size());
   auto& depInfo = _dependencyInfos[dependency];
 
@@ -258,7 +258,7 @@ std::pair<ExecutionState, size_t> MultiDependencySingleRowFetcher::skipRowsForDe
   TRI_ASSERT(!indexIsValid(depInfo));
   ExecutionState state;
   size_t skipped;
-  std::tie(state, skipped) = skipSomeForDependency(dependency, atMost, subqueryDepth);
+  std::tie(state, skipped) = skipSomeForDependency(dependency, atMost, 0);
   if (state == ExecutionState::HASMORE && skipped < atMost) {
     state = ExecutionState::DONE;
   }
@@ -349,11 +349,50 @@ bool MultiDependencySingleRowFetcher::fetchBlockIfNecessary(size_t const depende
   return true;
 }
 
-std::pair<ExecutionState, size_t> MultiDependencySingleRowFetcher::skipRows(
+std::pair<ExecutionState, size_t> MultiDependencySingleRowFetcher::skipSome(size_t atMost,
-    size_t const atMost, size_t const subqueryDepth) {
+                                                                            size_t subqueryDepth) {
-  // Must not be called for the current level
+  // Must not be called for the subqueryDepth == 0. It does not make sense for
+  // this fetcher to use anything but skipRowsForDependency() for the current level!
   TRI_ASSERT(subqueryDepth > 0);
-  // not yet implemented
+
-  TRI_ASSERT(false);
+  TRI_ASSERT(_nextSkipDependencyIndex < _dependencyInfos.size());
-  THROW_ARANGO_EXCEPTION(TRI_ERROR_NOT_IMPLEMENTED);
+
+  { // Skip deps that are DONE
+
+    // TODO Think this through. Is this necessary, and is it correct? What to do with DONE dependencies?
+    while (_nextSkipDependencyIndex < _dependencyInfos.size() &&
+           _dependencyInfos[_nextSkipDependencyIndex]._upstreamState == ExecutionState::DONE) {
+      auto& depInfo = _dependencyInfos[_nextSkipDependencyIndex];
+      // TODO skip local shadow rows with depth >= subqueryDepth first
+      depInfo._currentBlock = nullptr;
+      depInfo._rowIndex = 0;
+      ++_nextSkipDependencyIndex;
+    }
+    if (_nextSkipDependencyIndex >= _dependencyInfos.size()) {
+      _nextSkipDependencyIndex = 0;
+      return {ExecutionState::DONE, 0};
+    }
+  }
+
+  TRI_ASSERT(_nextSkipDependencyIndex < _dependencyInfos.size());
+
+  ExecutionState state{};
+  size_t skipped{};
+  while (_nextSkipDependencyIndex < _dependencyInfos.size()) {
+    auto& depInfo = _dependencyInfos[_nextSkipDependencyIndex];
+
+    // TODO skip local shadow rows with depth >= subqueryDepth first
+    std::tie(state, skipped) = _dependencyProxy->skipSome(atMost, subqueryDepth);
+    if (state == ExecutionState::WAITING) {
+      TRI_ASSERT(skipped = 0);
+      return {ExecutionState::WAITING, 0};
+    }
+    depInfo._currentBlock = nullptr;
+    depInfo._rowIndex = 0;
+    ++_nextSkipDependencyIndex;
+  }
+  TRI_ASSERT(_nextSkipDependencyIndex == _dependencyInfos.size());
+  TRI_ASSERT(state != ExecutionState::WAITING);
+
+  return {state, skipped};
 }

arangod/Aql/MultiDependencySingleRowFetcher.h

@@ -126,8 +126,7 @@ class MultiDependencySingleRowFetcher {
   TEST_VIRTUAL std::pair<ExecutionState, InputAqlItemRow> fetchRowForDependency(
       size_t dependency, size_t atMost = ExecutionBlock::DefaultBatchSize());
 
-  std::pair<ExecutionState, size_t> skipRowsForDependency(size_t dependency, size_t atMost,
+  std::pair<ExecutionState, size_t> skipRowsForDependency(size_t dependency, size_t atMost);
-                                                          size_t subqueryDepth);
 
   std::pair<ExecutionState, ShadowAqlItemRow> fetchShadowRow(
       size_t atMost = ExecutionBlock::DefaultBatchSize());
@@ -138,7 +137,7 @@ class MultiDependencySingleRowFetcher {
     THROW_ARANGO_EXCEPTION(TRI_ERROR_NOT_IMPLEMENTED);
   }
 
-  std::pair<ExecutionState, size_t> skipRows(size_t atMost, size_t subqueryDepth);
+  std::pair<ExecutionState, size_t> skipSome(size_t atMost, size_t subqueryDepth);
 
  private:
   DependencyProxy<BlockPassthrough::Disable>* _dependencyProxy;
@@ -148,6 +147,8 @@ class MultiDependencySingleRowFetcher {
    */
   std::vector<DependencyInfo> _dependencyInfos;
 
+  size_t _nextSkipDependencyIndex;
+
  private:
   /**
    * @brief Delegates to ExecutionBlock::fetchBlock()

arangod/Aql/SortingGatherExecutor.cpp

@@ -464,7 +464,7 @@ std::tuple<ExecutionState, SortingGatherExecutor::Stats, size_t> SortingGatherEx
     while (state != ExecutionState::DONE && _skipped < atMost) {
       std::size_t skippedNow;
       std::tie(state, skippedNow) =
-          _fetcher.skipRowsForDependency(_dependencyToFetch, 0, atMost - _skipped);
+          _fetcher.skipRowsForDependency(_dependencyToFetch, atMost - _skipped);
       if (state == ExecutionState::WAITING) {
         TRI_ASSERT(skippedNow == 0);
         return {state, NoStats{}, 0};

tests/Aql/MultiDepFetcherHelper.cpp

@@ -62,7 +62,7 @@ void arangodb::tests::aql::runFetcher(arangodb::aql::MultiDependencySingleRowFet
       void operator()(ConcreteFetcherIOPair<SkipRowsForDependency> const& iop) {
         auto const& args = iop.first;
         auto const& expected = iop.second;
-        auto actual = testee.skipRowsForDependency(args.dependency, args.atMost, 0);
+        auto actual = testee.skipRowsForDependency(args.dependency, args.atMost);
         EXPECT_EQ(expected, actual) << "during step " << i;
       }
       void operator()(ConcreteFetcherIOPair<FetchShadowRow> const& iop) {