[opt](dphyper)optimize dphyper's statistics calculation (#64559) - #68204
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Problem Summary:
After DPHyp join enumeration copies projected join alternatives into the
memo, the memo statistics are stale — DPHyp uses a lightweight heuristic
cost model that does not produce accurate row counts or column
distributions. Without a full statistics refresh, the subsequent
cascades optimization phase (OptimizeGroupJob) sees incorrect costs and
can produce suboptimal plans.
This PR introduces MemoStatsAndCostRecomputer, a bottom-up statistics
and cost recomputation pass that runs after DPHyp and before cascades
optimization. It re-estimates logical row counts for every memo group,
aggregates them according to a configurable policy, and rebuilds
physical costs from the refreshed statistics.
Key changes:
1. MemoStatsAndCostRecomputer (new)
- Bottom-up logical row-count re-estimation for every memo group.
- Trust-join-count aggregation policy: scores each candidate
expression by counting joins whose equal-join predicates have
high-confidence (ndv/rowCount > 0.9) column statistics, keeping
only the candidates with the most trusted joins.
- Per-group isStatsReliable tracking that stays consistent with the
selected/aggregated statistics instead of leaking from the last
candidate estimated in the loop.
- Project-group stats divergence protection: when two LogicalProject
alternatives diverge by >1000x in row count, the stats from the
currently-best PhysicalProject are preserved to avoid a misleading
aggregate (average/median).
- Two-pass logical re-estimation for CTE queries so consumers can
settle on refreshed producer stats.
- Physical-cost recomputation: clears and rebuilds per-group
lowest-cost-plan tables from the refreshed statistics.
2. countTrustJoins / getGroupTrustJoinCount
- Deterministic trust-join scoring: replaced child.getFirstLogical-
Expression() (memo-insertion-order dependent) with a per-group max
across all alternatives, memoized via groupTrustJoinCountCache.
- Cache is cleared before each logical re-estimation pass so CTE
producer stat changes are reflected.
3. hasTrustableEqualCondition (JoinEstimation)
- Rejects unknown column stats (ColumnStatistic.UNKNOWN) before the
NDV-ratio check. Unknown stats carry ndv=1, which could falsely
pass the >0.9 threshold on one-row tables.
4. GraphSimplifier cache isolation
- deriveStats and calCost now snapshot and restore their caches
between alternative join-order evaluations, preventing the second
alternative from reading column statistics derived for the first
alternative's join order.
5. DPHyp shape-check regression tests
- TPC-DS SF1000: 99 queries
- TPC-H SF1000: 22 queries
(cherry picked from commit 9e45962)
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pick #64559
What problem does this PR solve?
Issue Number: close #xxx
Related PR: #xxx
Problem Summary:
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