**Describe the situation**

```
SELECT * FROM test.hits INTO OUTFILE 'dump.csv' FORMAT CSV

8873898 rows in set. Elapsed: 32.487 sec. Processed 8.87 million rows, 8.46 GB (273.15 thousand rows/s., 260.42 MB/s.)
```

is bounded by single CPU core. Too slow :(
const char * next_query_begin = after_query_iterator->begin;
    // We include the entire line if the next query starts after
    // it. This is a generic case of trailing in-line comment.
    // The "equals" condition is for case of end of input (they both equal
    // all_queries_end
    if (newline )
    {
        assert(newline >= this_query_end
        this_query_end = newline;
    }
    else
    {
        // Many queries on one line, can't do anything. By the way, this
        // syntax is probably going to work as expected:
        // select nonexistent /* { serverError 12345 } */; select 1
    }
}
/// Convert external tables to ExternalTableData and send them using the connection.
void ClientBase::sendExternalTables(ASTPtr parsed_query)
{
    const auto * select = parsed_query->as<ASTSelectWithUnionQuery>(
    if (!select && !external_tables.empty())
        throw Exception("External tables could be sent only with select query", ErrorCodes::BAD_ARGUMENTS
    std::vector<ExternalTableDataPtr> data;
    for (auto & table : external_tables)
        data.emplace_back(table.getData(global_context)
    if (send_external_tables)
        connection->sendExternalTablesData(data
}
void ClientBase::onData(Block & block, ASTPtr parsed_query)