```sql
SELECT count()
FROM 
(
    SELECT number
    FROM numbers_mt(100000000)
    ORDER BY number DESC
    LIMIT 100
    UNION ALL
    SELECT number
    FROM numbers_mt(100000000)
    ORDER BY number DESC
    LIMIT 100
    UNION ALL
    SELECT number
    FROM numbers_mt(100000000)
    ORDER BY number DESC
    LIMIT 100
)


SET experimental_use_processors = 0;
-- 1 rows in set. Elapsed: 1.581 sec. Processed 300.00 million rows, 2.40 GB (189.78 million rows/s., 1.52 GB/s.) 

SET experimental_use_processors = 1;
-- 1 rows in set. Elapsed: 3.569 sec. Processed 300.00 million rows, 2.40 GB (84.06 million rows/s., 672.50 MB/s.) 
```

Similar for MergeTree:

```sql
create table test engine=MergeTree order by tuple() as select * from numbers(30000000);

select count() from (select number from test group by number order by number limit 10 union all select number from test group by number order by number limit 10);

set experimental_use_processors=0;
-- Elapsed: 2.664 sec

set experimental_use_processors=1;
-- Elapsed: 3.656 sec
```
}
        if (auto * port = pipe.getExtremesPort())
        {
            assertBlocksHaveEqualStructure(current_header, port->getHeader(), "QueryPipeline");
            extremes.emplace_back(port);
        }
        streams.addStream(&pipe.getPort(), pipe.maxParallelStreams());
        processors.emplace(std::move(pipe).detachProcessors());
    }
    if (!totals.empty())
    {
        if (totals.size() == 1)
            totals_having_port = totals.back();
        else
            totals_having_port = uniteTotals(totals, current_header, processors);
    }
    if (!extremes.empty())
    {
        if (extremes.size() == 1)
            extremes_port = extremes.back();
        else
            extremes_port = uniteExtremes(extremes, current_header, processors);
    }
}
static ProcessorPtr callProcessorGetter(
    const Block & header, const QueryPipeline::ProcessorGetter & getter, QueryPipeline::StreamType)
{
    return getter(header);
}
static ProcessorPtr callProcessorGetter(