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https://issues.apache.org/jira/browse/IMPALA-5861?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16758405#comment-16758405
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Tim Armstrong commented on IMPALA-5861:
---------------------------------------
This one looks so trivial we should just fix it.
> HdfsParquetScanner::GetNextInternal() IsZeroSlotTableScan() case double counts
> ------------------------------------------------------------------------------
>
> Key: IMPALA-5861
> URL: https://issues.apache.org/jira/browse/IMPALA-5861
> Project: IMPALA
> Issue Type: Bug
> Components: Backend
> Affects Versions: Impala 2.10.0
> Reporter: Dan Hecht
> Assignee: Tim Armstrong
> Priority: Major
>
> It appears that this code is double counting into {{rows_read_counter()}},
> since {{row_group_rows_read_}} is already accumulating:
> {code:title=HdfsParquetScanner::GetNextInternal()}
> } else if (scan_node_->IsZeroSlotTableScan()) {
> // There are no materialized slots and we are not optimizing count(*),
> e.g.
> // "select 1 from alltypes". We can serve this query from just the file
> metadata.
> // We don't need to read the column data.
> if (row_group_rows_read_ == file_metadata_.num_rows) {
> eos_ = true;
> return Status::OK();
> }
> assemble_rows_timer_.Start();
> DCHECK_LE(row_group_rows_read_, file_metadata_.num_rows);
> int64_t rows_remaining = file_metadata_.num_rows - row_group_rows_read_;
> int max_tuples = min<int64_t>(row_batch->capacity(), rows_remaining);
> TupleRow* current_row = row_batch->GetRow(row_batch->AddRow());
> int num_to_commit = WriteTemplateTuples(current_row, max_tuples);
> Status status = CommitRows(row_batch, num_to_commit);
> assemble_rows_timer_.Stop();
> RETURN_IF_ERROR(status);
> row_group_rows_read_ += num_to_commit;
> COUNTER_ADD(scan_node_->rows_read_counter(), row_group_rows_read_);
> <======
> return Status::OK();
> }
> {code}
> Repro in impala-shell:
> {noformat}
> set batch_size=16; set num_nodes=1; select count(*) from
> functional.alltypesmixedformat; profile
> ....
> - RowsRead: 3.94K (3936)
> - RowsReturned: 1.20K (1200)
> {noformat}
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