Loss of interactivity when streaming a large non-materialized result set

[philip-stoev]

What version of Materialize are you using?

v0.8.4-dev (f98fbfdc9)

What was the issue?

This is the original example @benesch gave in #1537. I am creating a separate ticket in order to add context and perf reports and also to underline that the problem this particular case exposed appears to be specifically about streaming large non-materialized results as opposed to e.g. join processing.

Is the issue reproducible? If so, please provide reproduction instructions.

drop view if exists v cascade; 
create materialized view v as values (1), (2), (3);
select * from v, v, v, v, v, v, v, v, v, v, v, v, v, v;

Interactivity is not lost if the select is wrapped inside a materialized view and then the same data is read off that view. The mz_scheduling_histogram of the materialized view does not have any extremes in the duration column.

The perf report looks like this:

-   18.35%    18.33%  tokio:work-12    materialized        [.] <alloc::vec::Vec<T,A> as alloc::vec::spec_extend::SpecExtend<T,I>>::spec_extend                                                               ◆
     16.46% <alloc::vec::Vec<T,A> as alloc::vec::spec_extend::SpecExtend<T,I>>::spec_extend                                                                                                                  ▒
-    5.13%     5.13%  tokio:work-12    materialized        [.] repr::row::read_datum                                                                                                                         ▒
   - 1.32% 0x400000003040000                                                                                                                                                                                 ▒
      - 1.19% 0x46                                                                                                                                                                                           ▒
           repr::row::read_datum                                                                                                                                                                             ▒
   - 1.28% 0x400000002040000                                                                                                                                                                                 ▒
      - 1.17% 0x46                                                                                                                                                                                           ▒
           repr::row::read_datum                                                                                                                                                                             ▒
   - 1.26% 0x400000001040000                                                                                                                                                                                 ▒
      - 1.16% 0x46                                                                                                                                                                                           ▒
           repr::row::read_datum                                                                                                                                                                             ▒
     1.07% repr::row::read_datum                                                                                                                                                                             ▒
-    4.88%     0.00%  tokio:work-12    [unknown]           [.] 0x00007f2ae89ef890                                                                                                                            ▒
   - 0x7f2ae89ef890                                                                                                                                                                                          ▒
        1.25% <bytes::bytes_mut::BytesMut as ore::fmt::FormatBuffer>::write_fmt                                                                                                                              ▒
        0.83% std::io::Write::write_fmt                                                                                                                                                                      ▒
        0.57% pgrepr::value::Value::encode_text                                                                                                                                                              ▒
        0.54% <pgwire::codec::Codec as tokio_util::codec::encoder::Encoder<pgwire::message::BackendMessage>>::encode                                                                                         ▒
        0.51% <bytes::bytes_mut::BytesMut as bytes::buf::buf_mut::BufMut>::put_slice                                                                                                                         ▒
-    4.59%     0.00%  tokio:work-12    [unknown]           [.] 0x0000000000000046                                                                                                                            ▒
   - 0x46                                                                                                                                                                                                    ▒
        3.52% repr::row::read_datum                                                                                                                                                                          ▒
        0.56% repr::row::Row::unpack                                                                                                                                                                         ▒
-    4.59%     0.00%  timely:work-1    [unknown]           [.] 0x0000000000000135                                                                                                                            ▒
   - 0x135                                                                                                                                                                                                   ▒
        4.14% repr::row::Row::try_pack                                                                                                                                                                       ▒
-    4.35%     0.00%  timely:work-1    [unknown]           [.] 0x1056394808568b48                                                                                                                            ▒
   - 0x1056394808568b48                                                                                                                                                                                      ▒
        2.53% <repr::row::DatumListIter as core::iter::traits::iterator::Iterator>::next                                                                                                                     ▒
        0.92% dataflow::render::join::linear_join::<impl dataflow::render::context::Context<G,repr::row::Row,T>>::differential_join_inner::{{closure}}                                                       ▒
+    4.14%     4.13%  timely:work-1    materialized        [.] repr::row::Row::try_pack                                                                                                                      ▒
+    3.62%     3.61%  tokio:work-12    materialized        [.] <alloc::vec::Vec<T> as alloc::vec::spec_from_iter::SpecFromIter<T,I>>::from_iter                                                              ▒
+    3.00%     3.00%  timely:work-1    materialized        [.] <alloc::vec::Vec<T,A> as alloc::vec::spec_extend::SpecExtend<T,I>>::spec_extend                                                               ▒
+    2.75%     2.75%  timely:work-1    materialized        [.] <repr::row::DatumListIter as core::iter::traits::iterator::Iterator>::next                                                                    ▒
+    2.74%     1.54%  timely:work-1    materialized        [.] smallvec::SmallVec<A>::insert_from_slice                                                                                                      ▒
+    2.30%     0.28%  timely:work-1    [kernel.kallsyms]   [k] page_fault                                                                                                                                    ▒
+    2.20%     2.20%  timely:work-1    materialized        [.] dataflow::render::join::linear_join::<impl dataflow::render::context::Context<G,repr::row::Row,T>>::differential_join_inner::{{closure}}      ▒
+    2.19%     2.19%  timely:work-1    libc-2.31.so        [.] __memcmp_avx2_movbe                                                                                                                           ▒
+    2.15%     0.00%  tokio:work-12    [unknown]           [.] 0x0400000003040000                                                                                                                            ▒
+    2.09%     0.00%  tokio:work-12    [unknown]           [.] 0x0400000002040000                                                                                                                            ▒
+    2.03%     0.00%  tokio:work-12    [unknown]           [.] 0x0400000001040000                                                                                                                            ▒
+    2.02%     0.00%  timely:work-1    [unknown]           [k] 0x0000000000000010                                                                                                                            ▒
+    2.02%     0.00%  timely:work-1    [kernel.kallsyms]   [k] do_page_fault                                                                                                                                 ▒
+    2.02%     0.01%  timely:work-1    [kernel.kallsyms]   [k] __do_page_fault                                                                                                       ```

[philip-stoev]

This appears fixed by #7171 . Other SQL clients can successfully issue queries while the cross join above is in progress.