HappenLee opened a new pull request, #68545:
URL: https://github.com/apache/doris/pull/68545
### What problem does this PR solve?
Issue Number: N/A
Related PR: #68246
Backport #68246 to `branch-4.1`. A zero `space_expand_rate` previously
produced a zero candidate capacity, so partial-state serialization discarded
every TOPN candidate and two-stage aggregation could return an empty result.
Treat non-positive rates as unlimited intermediate candidate retention for
`topn`, `topn_array`, and `topn_weighted`; `top_num` still limits the final
result. Positive and default rates retain their existing behavior.
Branch-specific conflict resolution:
- Keep the production fix, standalone TOPN unit tests, regression suite, and
the expected output generated in the original PR.
- Omit modifications to `agg_state_parameters_test.cpp` and
`test_agg_state_parameters.groovy`: neither file nor the associated
aggregate-state parameter validation exists in branch-4.1. This backport does
not introduce that separate master feature.
- Remove `SET enable_bucketed_hash_agg = false` from the regression suite
because branch-4.1 has no such session variable. Keep coverage for aggregation
phases 1 and 2.
### Release note
`topn`, `topn_array`, and `topn_weighted` interpret a non-positive
`space_expand_rate` as unlimited intermediate candidate retention. The final
result remains limited by `top_num`. Retaining all distinct candidates can
increase intermediate-state memory and network traffic.
### Check List (For Author)
- Test: Unit Test / Regression test included; local execution not completed
- Repository clang-format 16 formatting and check scripts passed.
- Diff whitespace check passed with the original generated `.out`
trailing blank line preserved.
- Attempted `./run-be-ut.sh -j 48 --run
--filter='AggregateFunctionTopN*.*:*/AggregateFunctionTopN*.*:AggTest.topn*'`.
Stopped during dependency preparation; the isolated checkout has no installed
third-party dependency bundle. No local 4.1 unit-test pass is claimed.
- Regression tests were not run locally against a 4.1 cluster. Expected
output is copied unchanged from #68246.
- Branch-4.1 does not contain `build-support/check-build-hygiene.sh`; no
successful hygiene or clang-tidy run is claimed.
- Behavior changed: Yes. Non-positive expansion rates retain all
intermediate candidates.
- Does this need documentation: Yes. The function documentation should
describe non-positive expansion rates; the documentation follow-up noted by
#68246 remains applicable.
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