Append row number column in batch reader (#78)

Summary:
Pull Request resolved: #78

We extend the nimble velox reader to support an additional row numbers column when present and also create a function to return the row number of the first row in the last read.

Differential Revision: D61506232

dwio/nimble/velox/FieldReader.cpp

@@ -1729,11 +1729,13 @@ class RowFieldReader final : public FieldReader {
       Decoder* decoder,
       std::vector<std::unique_ptr<FieldReader>> childrenReaders,
       Vector<bool>& boolBuffer,
-      folly::Executor* executor)
+      folly::Executor* executor,
+      bool withRowNumbersColumn)
       : FieldReader{pool, std::move(type), decoder},
         childrenReaders_{std::move(childrenReaders)},
         boolBuffer_{boolBuffer},
-        executor_{executor} {}
+        executor_{executor},
+        withRowNumbersColumn_{withRowNumbersColumn} {}
 
   std::optional<std::pair<uint32_t, uint64_t>> estimatedRowSize() const final {
     uint64_t totalBytes{0};
@@ -1791,8 +1793,17 @@ class RowFieldReader final : public FieldReader {
     auto rowCount = scatterCount(count, scatterBitmap);
     auto vector = VectorInitializer<velox::RowVector>::initialize(
         &pool_, output, type_, rowCount);
-    vector->children().resize(childrenReaders_.size());
     vector->unsafeResize(rowCount);
+
+    // If we determine that the presence of an additional child (representing
+    // row numbers) beyond those in the row's type, there is no need to resize
+    // its children since this only happens when the row vector is being reused.
+    bool reuseVector = withRowNumbersColumn_ &&
+        (vector->children().size() == type_->size() + 1);
+    if (!reuseVector) {
+      vector->children().resize(childrenReaders_.size());
+    }
+
     const void* childrenBits = nullptr;
     uint32_t selectedNonNullCount = 0;
 
@@ -1907,6 +1918,7 @@ class RowFieldReader final : public FieldReader {
   std::vector<std::unique_ptr<FieldReader>> childrenReaders_;
   Vector<bool>& boolBuffer_;
   folly::Executor* executor_;
+  bool withRowNumbersColumn_;
 };
 
 class RowFieldReaderFactory final : public FieldReaderFactory {
@@ -1917,11 +1929,13 @@ class RowFieldReaderFactory final : public FieldReaderFactory {
       velox::TypePtr veloxType,
       const Type* type,
       std::vector<std::unique_ptr<FieldReaderFactory>> children,
-      folly::Executor* executor)
+      folly::Executor* executor,
+      bool withRowNumbersColumn)
       : FieldReaderFactory{pool, std::move(veloxType), type},
         children_{std::move(children)},
         boolBuffer_{&pool_},
-        executor_{executor} {}
+        executor_{executor},
+        withRowNumbersColumn_{withRowNumbersColumn} {}
 
   std::unique_ptr<FieldReader> createReader(
       const folly::F14FastMap<offset_size, std::unique_ptr<Decoder>>& decoders)
@@ -1944,7 +1958,8 @@ class RowFieldReaderFactory final : public FieldReaderFactory {
           nulls,
           std::move(childrenReaders),
           boolBuffer_,
-          executor_);
+          executor_,
+          withRowNumbersColumn_);
     }
 
     return std::make_unique<RowFieldReader<true>>(
@@ -1953,13 +1968,15 @@ class RowFieldReaderFactory final : public FieldReaderFactory {
         nulls,
         std::move(childrenReaders),
         boolBuffer_,
-        executor_);
+        executor_,
+        withRowNumbersColumn_);
   }
 
  private:
   std::vector<std::unique_ptr<FieldReaderFactory>> children_;
   Vector<bool> boolBuffer_;
   folly::Executor* executor_;
+  bool withRowNumbersColumn_;
 };
 
 // Represent a keyed value node for flat map
@@ -2886,6 +2903,9 @@ std::unique_ptr<FieldReaderFactory> createFieldReaderFactory(
         children.push_back(std::move(factory));
       }
 
+      // Support row number column only at root level.
+      bool withRowNumbersColumn = level == 0 && parameters.withRowNumbersColumn;
+
       // Underlying reader may return a different vector type than what
       // specified, (eg. flat map read as struct). So create new ROW type based
       // on children types. Note this special logic is only for Row type based
@@ -2897,7 +2917,8 @@ std::unique_ptr<FieldReaderFactory> createFieldReaderFactory(
               std::move(childTypes)),
           nimbleType.get(),
           std::move(children),
-          executor);
+          executor,
+          withRowNumbersColumn);
     }
     case velox::TypeKind::MAP: {
       NIMBLE_CHECK(

dwio/nimble/velox/FieldReader.h

@@ -51,6 +51,10 @@ struct FieldReaderParams {
   // Callback to populate feature projection stats when needed
   std::function<void(velox::dwio::common::flatmap::FlatMapKeySelectionStats)>
       keySelectionCallback{nullptr};
+
+  // If true, we'll expect a row number column to be present as the last child
+  // of each velox row vector.
+  bool withRowNumbersColumn{false};
 };
 
 class FieldReader {

dwio/nimble/velox/VeloxReader.cpp

@@ -260,6 +260,7 @@ VeloxReader::VeloxReader(
         lastRow_ = rows + stripeRowCount;
       }
     }
+    firstRowInStripe_[i] = rows;
     rows += stripeRowCount;
   }
 
@@ -372,13 +373,10 @@ uint64_t VeloxReader::estimatedRowSize() {
 }
 
 bool VeloxReader::next(uint64_t rowCount, velox::VectorPtr& result) {
-  if (rowsRemainingInStripe_ == 0) {
-    if (nextStripe_ < lastStripe_) {
-      loadNextStripe();
-    } else {
-      return false;
-    }
+  if (!hasMoreRows()) {
+    return false;
   }
+
   uint64_t rowsToRead = std::min(rowsRemainingInStripe_, rowCount);
   std::optional<std::chrono::steady_clock::time_point> startTime;
   if (parameters_.decodingTimeCallback) {
@@ -547,4 +545,22 @@ uint32_t VeloxReader::getCurrentRowInStripe() const {
       static_cast<uint32_t>(rowsRemainingInStripe_);
 }
 
+uint64_t VeloxReader::getRowNumber() {
+  if (hasMoreRows()) {
+    return firstRowInStripe_[loadedStripe_.value()] + getCurrentRowInStripe();
+  }
+  return lastRow_;
+}
+
+bool VeloxReader::hasMoreRows() {
+  if (rowsRemainingInStripe_ == 0) {
+    if (nextStripe_ < lastStripe_) {
+      loadNextStripe();
+    } else {
+      return false;
+    }
+  }
+  return true;
+}
+
 } // namespace facebook::nimble

dwio/nimble/velox/VeloxReader.h

@@ -114,6 +114,10 @@ class VeloxReader {
     return pool_;
   }
 
+  // Returns the current row number the reader is pointing to. If there are no
+  // more rows to read in the file, this will return the last row number.
+  uint64_t getRowNumber();
+
   // Seeks to |rowNumber| from the beginning of the file (row 0).
   // If |rowNumber| is greater than the number of rows in the file, the
   // seek will stop at the end of file and following reads will return
@@ -163,6 +167,8 @@ class VeloxReader {
 
   uint32_t getCurrentRowInStripe() const;
 
+  bool hasMoreRows();
+
   velox::memory::MemoryPool& pool_;
   std::shared_ptr<const TabletReader> tabletReader_;
   std::optional<TabletReader::StripeIdentifier> stripeIdentifier_;
@@ -174,6 +180,7 @@ class VeloxReader {
   std::unique_ptr<FieldReaderFactory> rootFieldReaderFactory_;
   std::unique_ptr<FieldReader> rootReader_;
   mutable std::optional<std::map<std::string, std::string>> metadata_;
+  std::map<uint32_t, uint64_t> firstRowInStripe_;
   uint32_t firstStripe_;
   uint32_t lastStripe_;
   uint64_t firstRow_;