```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
```
{
    checkInitializedAndNotCompleted();
    checkSource(source, false);
    assertBlocksHaveEqualStructure(current_header, source->getOutputs().front().getHeader(), "QueryPipeline");
    IProcessor::PortNumbers delayed_streams = { streams.size() };
    streams.addStream(&source->getOutputs().front(), 0);
    processors.emplace(std::move(source));
    auto processor = std::make_shared<DelayedPortsProcessor>(current_header, streams.size(), delayed_streams);
    addPipe({ std::move(processor) });
}
void QueryPipeline::resize(size_t num_streams, bool force, bool strict)