Description of Changes

Avoid building a temporary Vec in execute_plan by exposing a list-building interface instead.

• The old fn encode_list is rewritten in terms of this list-building interface.
• The BsatnRowList and BsatnRowListBuilder types are split into two entirely separate types. The latter now tries to recognize the case where there isn't a known static layout, but where the BSATN lengths happen to be the same for all rows anyways. In those cases, the allocation of RowSizeHint::RowOffsets is avoided in favor of just storing the found length in bytes. This is in particular useful for small table updates as statistically, the fewer rows, the more chance of the lengths being all equal. In the case of a single row, the chance is notably 100%. It is also good for the case of when we don't have RelValue::Row or Row::Ptr but where the underlying table that actually has a static layout.

In the future, we might want to avoid these lists in incremental as well.

Benchmarks

Benchmark numbers vs. master using cargo bench --bench subscription -- --baseline subs on i7-7700K, 64GB RAM:

footprint-scan          time:   [28.731 ms 28.924 ms 29.171 ms]
                        change: [-49.728% -49.006% -48.388%] (p = 0.00 < 0.05)
                        Performance has improved.

Performance goes from roughly 56.721 ms to 28.795 ms.

API and ABI breaking changes

None

Expected complexity level and risk

2, fairly local change to just subscriptions.

Testing

Covered by existing tests.