LuciferYang commented on issue #9883:
URL: https://github.com/apache/paimon/issues/9883#issuecomment-5710616065

   Scope update: #9909 fixes the fully-unevaluable half of this issue (the 
scalar index cannot evaluate the predicate at all, so the old empty bitmap 
dropped every index-covered row). It intentionally does not close this issue.
   
   Still open here: a partially-evaluable predicate keeps the index fast path 
and can return a wrong top-K, because the scalar evaluator drops the 
unsupported conjunct and returns a non-null superset. Two shapes:
   
   - different fields, e.g. `a = 1 AND tags IS NOT NULL` where the array 
conjunct is unsupported;
   - same field, e.g. `id >= 0 AND CAST(id AS BIGINT) > 0` where the CAST 
conjunct is unsupported.
   
   Field coverage (`contributingFieldIds`) is not sufficient to prove 
exactness: the second shape covers every referenced field yet is still inexact. 
A fix needs an expression-level exactness signal or residual predicate from the 
evaluator, then either raw fallback or candidate re-checking with extra 
retrieval to refill the filtered top-K (filtering only the initial K would 
still miss qualifying rows displaced from that candidate set).
   


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