fatemehp commented on code in PR #14142:
URL: https://github.com/apache/arrow/pull/14142#discussion_r975741230
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cpp/src/parquet/column_reader.cc:
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@@ -1328,6 +1329,156 @@ class TypedRecordReader : public
ColumnReaderImplBase<DType>,
return records_read;
}
+
+ // Skip records that we have in our buffer. This function is only for
+ // non-repeated fields.
+ int64_t SkipRecordsInBufferNonRepeated(int64_t num_records) {
+ ARROW_DCHECK(this->max_rep_level_ == 0);
+ ARROW_DCHECK(this->has_values_to_process());
+
+ int64_t remaining_records = levels_written_ - levels_position_;
+ int64_t skipped_records = std::min(num_records, remaining_records);
+ int64_t start_levels_position = levels_position_;
+ // Since there is no repetition, number of levels equals number of records.
+ levels_position_ += skipped_records;
+ // We skipped the levels by incrementing 'levels_position_'. For values
+ // we do not have a buffer, so we need to read them and throw them away.
+ // First we need to figure out how many present/not-null values there are.
+ std::shared_ptr<::arrow::ResizableBuffer> valid_bits;
+ valid_bits = AllocateBuffer(this->pool_);
+ PARQUET_THROW_NOT_OK(
+ valid_bits->Resize(bit_util::BytesForBits(skipped_records), true));
+ ValidityBitmapInputOutput validity_io;
+ validity_io.values_read_upper_bound = skipped_records;
+ validity_io.valid_bits = valid_bits->mutable_data();
+ validity_io.valid_bits_offset = 0;
+ DefLevelsToBitmap(def_levels() + start_levels_position,
+ levels_position_ - start_levels_position,
+ this->leaf_info_, &validity_io);
+ int64_t values_to_read = validity_io.values_read - validity_io.null_count;
+ ReadAndThrowAway(values_to_read);
+ // Mark the levels as read in the underlying column reader.
+ this->ConsumeBufferedValues(skipped_records);
+ return skipped_records;
+ }
+
+ // Skip records for repeated fields. Returns number of skipped records.
+ // Skip records for repeated fields. Returns number of skipped records.
+ int64_t SkipRecordsRepeated(int64_t num_records) {
+ ARROW_DCHECK_GT(this->max_rep_level_, 0);
+
+ // For repeated fields, we are technically reading and throwing away the
+ // levels and values since we do not know the record boundaries in advance.
+ // Keep filling the buffer and skipping until we reach the desired number
+ // of records or we run out of values in the column chunk.
+ int64_t skipped_records = 0;
+ int64_t level_batch_size = std::max<int>(kMinLevelBatchSize, num_records);
+ // If 'at_record_start_' is false, but (skip_records == num_records), it
+ // means that for the last record that was counted, we have not seen all
+ // of it's values yet.
+ while (!at_record_start_ || skipped_records < num_records) {
+ // Is there more data to read in this row group?
+ // HasNextInternal() will advance to the next page if necessary.
+ if (!this->HasNextInternal()) {
+ if (!at_record_start_) {
+ // We ended the row group while inside a record that we haven't seen
+ // the end of yet. So increment the record count for the last record
+ // in the row group
+ ++skipped_records;
+ at_record_start_ = true;
+ }
+ break;
+ }
+
+ // Read some more levels.
+ int64_t batch_size =
+ std::min(level_batch_size, available_values_current_page());
+ // No more data in column. This must be an empty page.
+ // If we had exhausted the last page, HasNextInternal() must have
advanced
+ // to the next page. So there must be available values to process.
+ if (batch_size == 0) {
+ break;
+ }
+
+ ReserveLevels(batch_size);
+
+ int16_t* def_levels = this->def_levels() + levels_written_;
Review Comment:
When reading repetition and definition levels, we append them to the buffer
that we already have. When we figure out how many of those we need to skip, we
shift the values to the left to skip them.
Your comment revealed a bug where I was not shifting the values. I fixed it
and checked that in the tests.
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