Also make joins between two index scans individually observable.

src/engine/IndexScan.cpp

@@ -204,15 +204,25 @@
 }
 
 // _____________________________________________________________________________
-Result::Generator IndexScan::chunkedIndexScan() const {
+Result::Generator IndexScan::chunkedIndexScan() {
   auto optBlockSpan = getBlockMetadata();
   if (!optBlockSpan.has_value()) {
     co_return;
   }
   const auto& blockSpan = optBlockSpan.value();
+  size_t numBlocksAll = blockSpan.size();
   // Note: Given a `PrefilterIndexPair` is available, the corresponding
   // prefiltering will be applied in `getLazyScan`.
-  for (IdTable& idTable : getLazyScan({blockSpan.begin(), blockSpan.end()})) {
+  auto innerGenerator = getLazyScan({blockSpan.begin(), blockSpan.end()});
+  auto setDetails = ad_utility::makeOnDestructionDontThrowDuringStackUnwinding(
+      [
+
+          this, numBlocksAll, &innerGenerator]() {
+        auto details = innerGenerator.details();
+        details.numBlocksAll_ = numBlocksAll;
+        updateRuntimeInfoForLazyScan(details);
+      });
+  for (IdTable& idTable : innerGenerator) {
     co_yield {std::move(idTable), LocalVocab{}};
   }
 }
@@ -339,7 +349,14 @@
 // _____________________________________________________________________________
 std::optional<std::vector<CompressedBlockMetadata>>
 IndexScan::getBlockMetadataOptionallyPrefiltered() const {
-  auto optBlockSpan = getBlockMetadata();
+  auto optBlockSpan =
+      [&]() -> std::optional<std::span<const CompressedBlockMetadata>> {
+    if (prefilteredBlocks_.has_value()) {
+      return prefilteredBlocks_.value();
+    } else {
+      return getBlockMetadata();
+    }
+  }();
   std::optional<std::vector<CompressedBlockMetadata>> optBlocks = std::nullopt;
   if (optBlockSpan.has_value()) {
     const auto& blockSpan = optBlockSpan.value();
@@ -389,6 +406,7 @@
 };
 
 // _____________________________________________________________________________
+// TODO<joka921> This can be removed now.
 std::array<Permutation::IdTableGenerator, 2>
 IndexScan::lazyScanForJoinOfTwoScans(const IndexScan& s1, const IndexScan& s2) {
   AD_CONTRACT_CHECK(s1.numVariables_ <= 3 && s2.numVariables_ <= 3);
@@ -656,3 +674,57 @@
   return {createPrefilteredJoinSide(state),
           createPrefilteredIndexScanSide(state)};
 }
+
+// _____________________________________________________________________________
+void IndexScan::setBlocksForJoinOfIndexScans(Operation* left,
+                                             Operation* right) {
+  auto& leftScan = dynamic_cast<IndexScan&>(*left);
+  auto& rightScan = dynamic_cast<IndexScan&>(*right);
+
+  auto getBlocks = [](IndexScan& scan) {
+    auto metaBlocks = scan.getMetadataForScan();
+    if (!metaBlocks.has_value()) {
+      return metaBlocks;
+    }
+    if (scan.prefilteredBlocks_.has_value()) {
+      metaBlocks.value().blockMetadata_ = scan.prefilteredBlocks_.value();
+    }
+    return metaBlocks;
+  };
+
+  auto metaBlocks1 = getBlocks(leftScan);
+  auto metaBlocks2 = getBlocks(rightScan);
+  if (!metaBlocks1.has_value() || !metaBlocks2.has_value()) {
+    return;
+  }
+  auto [blocks1, blocks2] = CompressedRelationReader::getBlocksForJoin(
+      metaBlocks1.value(), metaBlocks2.value());
+  leftScan.prefilteredBlocks_ = std::move(blocks1);
+  rightScan.prefilteredBlocks_ = std::move(blocks2);
+}
+
+// _____________________________________________________________________________
+std::vector<Operation*> IndexScan::getIndexScansForSortVariables(
+    std::span<const Variable> variables) {
+  const auto& sorted = resultSortedOn();
+  if (resultSortedOn().size() < variables.size()) {
+    return {};
+  }
+  const auto& varColMap = getExternallyVisibleVariableColumns();
+  for (size_t i = 0; i < variables.size(); ++i) {
+    auto it = varColMap.find(variables[i]);
+    if (it == varColMap.end() ||
+        it->second.columnIndex_ != resultSortedOn().at(i)) {
+      return {};
+    }
+  }
+  return {this};
+}
+
+// _____________________________________________________________________________
+void IndexScan::setPrefilteredBlocks(
+    std::vector<CompressedBlockMetadata> prefilteredBlocks) {
+  prefilteredBlocks_ = std::move(prefilteredBlocks);
+  // TODO<joka921> once the other PR is merged we have to assert that the result
+  // is never cached AD_CORRECTNESS_CHECK(!canBeStoredInCache());
+}

src/engine/IndexScan.h

@@ -36,6 +36,9 @@ class IndexScan final : public Operation {
   std::vector<ColumnIndex> additionalColumns_;
   std::vector<Variable> additionalVariables_;
 
+  // TODO<joka921> Comment
+  std::optional<std::vector<CompressedBlockMetadata>> prefilteredBlocks_;
+
  public:
   IndexScan(QueryExecutionContext* qec, Permutation::Enum permutation,
             const SparqlTriple& triple, Graphs graphsToFilter = std::nullopt,
@@ -108,6 +111,9 @@ class IndexScan final : public Operation {
   std::pair<Result::Generator, Result::Generator> prefilterTables(
       Result::Generator input, ColumnIndex joinColumn);
 
+  // TODO<joka921> Comment
+  static void setBlocksForJoinOfIndexScans(Operation* left, Operation* right);
+
  private:
   // Implementation detail that allows to consume a generator from two other
   // cooperating generators. Needs to be forward declared as it is used by
@@ -202,7 +208,7 @@ class IndexScan final : public Operation {
       PrefilterIndexPair prefilter) const;
 
   // Return the (lazy) `IdTable` for this `IndexScan` in chunks.
-  Result::Generator chunkedIndexScan() const;
+  Result::Generator chunkedIndexScan();
   // Get the `IdTable` for this `IndexScan` in one piece.
   IdTable materializedIndexScan() const;
 
@@ -234,4 +240,11 @@ class IndexScan final : public Operation {
   Permutation::IdTableGenerator getLazyScan(
       std::vector<CompressedBlockMetadata> blocks) const;
   std::optional<Permutation::MetadataAndBlocks> getMetadataForScan() const;
+
+  // TODO<joka921> Comment.
+  void setPrefilteredBlocks(
+      std::vector<CompressedBlockMetadata> prefilteredBlocks);
+
+  std::vector<Operation*> getIndexScansForSortVariables(
+      std::span<const Variable> variables) override;
 };

src/engine/Join.cpp

@@ -181,6 +181,16 @@
   auto rightResIfCached = getCachedOrSmallResult(*_right);
   checkCancellation();
 
+  // TODO<joka921> Copy and move to separate function.
+  std::span joinVarSpan{&_joinVar, 1};
+  auto leftIndexScans = _left->getIndexScansForSortVariables(joinVarSpan);
+  auto rightIndexScans = _right->getIndexScansForSortVariables(joinVarSpan);
+  for (auto* left : leftIndexScans) {
+    for (auto* right : rightIndexScans) {
+      IndexScan::setBlocksForJoinOfIndexScans(left, right);
+    }
+  }
+
   auto leftIndexScan =
       std::dynamic_pointer_cast<IndexScan>(_left->getRootOperation());
   if (leftIndexScan &&
@@ -189,9 +199,6 @@
       AD_CORRECTNESS_CHECK(rightResIfCached->isFullyMaterialized());
       return computeResultForIndexScanAndIdTable<true>(
           requestLaziness, std::move(rightResIfCached), leftIndexScan);
-
-    } else if (!leftResIfCached) {
-      return computeResultForTwoIndexScans(requestLaziness);
     }
   }
 
@@ -216,9 +223,10 @@
     if (leftRes->isFullyMaterialized()) {
       return computeResultForIndexScanAndIdTable<false>(
           requestLaziness, std::move(leftRes), rightIndexScan);
+    } else if (!leftIndexScan) {
+      return computeResultForIndexScanAndLazyOperation(
+          requestLaziness, std::move(leftRes), rightIndexScan);
     }
-    return computeResultForIndexScanAndLazyOperation(
-        requestLaziness, std::move(leftRes), rightIndexScan);
   }
 
   std::shared_ptr<const Result> rightRes =
@@ -647,47 +655,6 @@
   }
 }
 
-// ______________________________________________________________________________________________________
-ProtoResult Join::computeResultForTwoIndexScans(bool requestLaziness) const {
-  return createResult(
-      requestLaziness,
-      [this](std::function<void(IdTable&, LocalVocab&)> yieldTable) {
-        auto leftScan =
-            std::dynamic_pointer_cast<IndexScan>(_left->getRootOperation());
-        auto rightScan =
-            std::dynamic_pointer_cast<IndexScan>(_right->getRootOperation());
-        AD_CORRECTNESS_CHECK(leftScan && rightScan);
-        // The join column already is the first column in both inputs, so we
-        // don't have to permute the inputs and results for the
-        // `AddCombinedRowToIdTable` class to work correctly.
-        AD_CORRECTNESS_CHECK(_leftJoinCol == 0 && _rightJoinCol == 0);
-        auto rowAdder = makeRowAdder(std::move(yieldTable));
-
-        ad_utility::Timer timer{
-            ad_utility::timer::Timer::InitialStatus::Started};
-        auto [leftBlocksInternal, rightBlocksInternal] =
-            IndexScan::lazyScanForJoinOfTwoScans(*leftScan, *rightScan);
-        runtimeInfo().addDetail("time-for-filtering-blocks", timer.msecs());
-
-        auto leftBlocks = convertGenerator(std::move(leftBlocksInternal));
-        auto rightBlocks = convertGenerator(std::move(rightBlocksInternal));
-
-        ad_utility::zipperJoinForBlocksWithoutUndef(leftBlocks, rightBlocks,
-                                                    std::less{}, rowAdder);
-
-        leftScan->updateRuntimeInfoForLazyScan(leftBlocks.details());
-        rightScan->updateRuntimeInfoForLazyScan(rightBlocks.details());
-
-        AD_CORRECTNESS_CHECK(leftBlocks.details().numBlocksRead_ <=
-                             rightBlocks.details().numElementsRead_);
-        AD_CORRECTNESS_CHECK(rightBlocks.details().numBlocksRead_ <=
-                             leftBlocks.details().numElementsRead_);
-        auto localVocab = std::move(rowAdder.localVocab());
-        return Result::IdTableVocabPair{std::move(rowAdder).resultTable(),
-                                        std::move(localVocab)};
-      });
-}
-
 // ______________________________________________________________________________________________________
 template <bool idTableIsRightInput>
 ProtoResult Join::computeResultForIndexScanAndIdTable(
@@ -834,3 +801,11 @@
       1, IdTable{getResultWidth(), allocator()}, cancellationHandle_,
       CHUNK_SIZE, std::move(callback)};
 }
+// _____________________________________________________________________________
+std::vector<Operation*> Join::getIndexScansForSortVariables(
+    std::span<const Variable> variables) {
+  auto result = _left->getIndexScansForSortVariables(variables);
+  auto right = _right->getIndexScansForSortVariables(variables);
+  result.insert(result.end(), right.begin(), right.end());
+  return result;
+}

src/engine/Join.h

@@ -141,6 +141,10 @@ class Join : public Operation {
   static void hashJoin(const IdTable& dynA, ColumnIndex jc1,
                        const IdTable& dynB, ColumnIndex jc2, IdTable* dynRes);
 
+  // TODO<joka921> Comment.
+  std::vector<Operation*> getIndexScansForSortVariables(
+      std::span<const Variable> variables) override;
+
  protected:
   virtual string getCacheKeyImpl() const override;
 
@@ -149,11 +153,6 @@ class Join : public Operation {
 
   VariableToColumnMap computeVariableToColumnMap() const override;
 
-  // A special implementation that is called when both children are
-  // `IndexScan`s. Uses the lazy scans to only retrieve the subset of the
-  // `IndexScan`s that is actually needed without fully materializing them.
-  ProtoResult computeResultForTwoIndexScans(bool requestLaziness) const;
-
   // A special implementation that is called when exactly one of the children is
   // an `IndexScan` and the other one is a fully materialized result. The
   // argument `idTableIsRightInput` determines whether the `IndexScan` is the

src/engine/Operation.h

@@ -426,6 +426,12 @@ class Operation {
       RuntimeInformation::Status status =
           RuntimeInformation::Status::optimizedOut);
 
+  // TODO<joka921> Comment.
+  virtual std::vector<Operation*> getIndexScansForSortVariables(
+      [[maybe_unused]] std::span<const Variable> variables) {
+    return {};
+  }
+
  private:
   // Create the runtime information in case the evaluation of this operation has
   // failed.

src/engine/QueryExecutionTree.cpp

@@ -225,3 +225,18 @@ QueryExecutionTree::getVariableAndInfoByColumnIndex(ColumnIndex colIdx) const {
   AD_CONTRACT_CHECK(it != varColMap.end());
   return *it;
 }
+
+// _____________________________________________________________________________
+std::vector<Operation*> QueryExecutionTree::getIndexScansForSortVariables(
+    std::span<const Variable> variables) {
+  auto result = rootOperation_->getIndexScansForSortVariables(variables);
+  if (result.empty()) {
+    return result;
+  }
+  // TODO<joka921> We have to disable the caching as soon as the PR for that is
+  // merged.
+  // rootOperation_->disableCaching();
+  cachedResult_.reset();
+  sizeEstimate_.reset();
+  return result;
+}

src/engine/QueryExecutionTree.h

@@ -122,6 +122,10 @@ class QueryExecutionTree {
     return rootOperation_->collectWarnings();
   }
 
+  // TODO<joka921> Comment.
+  virtual std::vector<Operation*> getIndexScansForSortVariables(
+      std::span<const Variable> variables) final;
+
   template <typename F>
   void forAllDescendants(F f) {
     static_assert(

src/index/CompressedRelation.h

@@ -466,7 +466,7 @@ class CompressedRelationReader {
   // to be performed.
   struct ScanSpecAndBlocks {
     ScanSpecification scanSpec_;
-    const std::span<const CompressedBlockMetadata> blockMetadata_;
+    std::span<const CompressedBlockMetadata> blockMetadata_;
   };
 
   // This struct additionally contains the first and last triple of the scan