Alena0704 opened a new pull request, #1937:
URL: https://github.com/apache/cloudberry/pull/1937
gp_percentile_cont() / gp_percentile_disc() are the split ordered-set
aggregates ORCA rewrites percentile_cont(), percentile_disc() and median()
into. Two bugs in their transition functions. Only the ORCA path reaches
these aggregates on its own, so percentile_* WITHIN GROUP on the Postgres
planner is unaffected.
1. The catalog declares the wrong number of arguments
The transition functions read five arguments in C (state + the four
aggregate arguments), but pg_proc.dat declares four. As transition
functions they are called correctly; a direct SQL call makes
PG_GETARG_INT64(4) pick up garbage — wrong results, an assertion on
pfree(NULL), or a segfault.
2. The isnull flag is lost when the previous state is returned
When the current row isn't one the percentile is computed from, the
previous state is handed back untouched. On the first call that state is
NULL, and returning a bare Datum(0) with isnull false drops the flag: 0
instead of NULL for by-value types, a NULL pointer dereference for
by-reference ones — an empty input set crashed the backend for interval,
timestamp and timestamptz.
Both ported from Greengage commit 477b04a (ADBDEV-7770).
The bug reproduction:
```
-- Bug 1: pg_proc.dat declares four arguments, the code reads five
select gp_percentile_disc_transition(NULL::numeric, 1, 1, 1); -- garbage or
crash
-- after the fix the five-argument form resolves and works:
select gp_percentile_disc_transition(NULL::numeric, 1::numeric, 1, 1, 1);
-- 1
-- Bug 2, by-value: silently wrong answer
select gp_percentile_cont(0::float8, 0, 0, 0); -- 0, expecting
NULL
-- Bug 2, by-reference: backend crash
select gp_percentile_cont('0 hour'::interval, 0, 0, 0); -- server closed
the connection
-- Bug 2, the 6c289ad regression: a selected value whose Datum is 0 turns
into NULL
select gp_percentile_disc(0::float8, 0, 1, 1); -- NULL,
expecting 0
select gp_percentile_disc(0::int, 0, 1, 1); -- NULL,
expecting 0
-- The same, end to end: ORCA and the Postgres planner disagree
create table perczero (a int, b float8) distributed by (a);
insert into perczero select i, (i - 1)::float8 from generate_series(1, 10) i;
select percentile_disc(0) within group (order by b) from perczero; -- NULL
set optimizer = off;
select percentile_disc(0) within group (order by b) from perczero; -- 0
```
### Type of Change
- [x] Bug fix (non-breaking change)
- [ ] New feature (non-breaking change)
- [ ] Breaking change (fix or feature with breaking changes)
- [ ] Documentation update
### Breaking Changes
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### Test Plan
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- [ ] Unit tests added/updated
- [ ] Integration tests added/updated
- [ ] Passed `make installcheck`
- [ ] Passed `make -C src/test installcheck-cbdb-parallel`
### Impact
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**Performance:**
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**User-facing changes:**
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**Dependencies:**
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### Checklist
- [x] Followed [contribution
guide](https://cloudberry.apache.org/contribute/code)
- [ ] Added/updated documentation
- [ ] Reviewed code for security implications
- [ ] This PR contains AI-assisted code generation
- [x] Requested review from [cloudberry
committers](https://github.com/orgs/apache/teams/cloudberry-committers)
### Additional Context
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