Method FinalizeTupleTransfer

be/src/exec/scratch-tuple-batch.h:124–150

Finalize transfer of 'num_to_commit' tuples to 'dst_batch' and transfer memory to 'dst_batch' if at the end of 'scratch_batch'. The tuples must not yet be committed to 'dst_batch'. Only needs to be called when materialising non-empty tuples.

  /// committed to 'dst_batch'. Only needs to be called when materialising non-empty
  /// tuples.
  void FinalizeTupleTransfer(RowBatch* dst_batch, int num_to_commit) {
    DCHECK_GE(num_to_commit, 0);
    DCHECK_LE(dst_batch->num_rows() + num_to_commit, dst_batch->capacity());
    DCHECK_LE(num_tuples_transferred + num_to_commit, num_tuples);
    DCHECK(tuple_mem != nullptr);
    num_tuples_transferred += num_to_commit;
    if (!AtEnd()) return;
    // We're at the end of the scratch batch. Transfer memory that may be referenced by
    // transferred tuples or that we can't reuse to 'dst_batch'.

    // Future tuples won't reference data in 'aux_mem_pool' - always transfer so that
    // we don't accumulate unneeded memory in the scratch batch.
    dst_batch->tuple_data_pool()->AcquireData(&aux_mem_pool, false);

    // Try to avoid the transfer of 'tuple_mem' for selective scans by compacting the
    // output batch. This avoids excessive allocation and transfer of memory, which
    // can lead to performance problems like IMPALA-4923.
    // Compaction is unsafe if the scratch batch was split across multiple output batches
    // because the batch we returned earlier may hold a reference into 'tuple_mem'.
    if (num_tuples_transferred > num_to_commit
        || num_tuples_transferred * MIN_SELECTIVITY_TO_COMPACT > num_tuples
        || !TryCompact(dst_batch, num_to_commit)) {
      // Didn't compact - rows in 'dst_batch' reference 'tuple_mem'.
      dst_batch->tuple_data_pool()->AcquireData(&tuple_mem_pool, false);
      tuple_mem = nullptr;
    }
  }

  /// Try to compact 'num_uncommitted_tuples' uncommitted tuples that were added to
  /// the end of 'dst_batch' by copying them to memory allocated from