malinjawi commented on issue #9003:
URL: https://github.com/apache/gluten/issues/9003#issuecomment-5895372728

   > [@philo-he](https://github.com/philo-he) 
[@zhztheplayer](https://github.com/zhztheplayer), 
[@malinjawi](https://github.com/malinjawi) I wanted to raise this issue as it 
is the main cause of Delta UT failures, 226 of 963 failures are because of 
this, besides the fact that it is providing incorrect metrics in the Delta Log.
   
   @felipepessoto thanks for the push on this, I picked it up. Root cause is on 
our side: the Delta project transformer strips every IncrementMetric and the 
metrics updater credits each one with the operator's output rows, so the 
counters MERGE keeps inside its CASE WHEN branches get every row. That's also 
why a no-op MERGE shows changes in CDF.
   
   Fix is up in #13158: we only offload an IncrementMetric where Spark would 
evaluate it once per output row, everything else stays on Spark. DELETE/UPDATE 
keep their offload, only MERGE's write projection falls back. 
   
   @rui-mo to your question: the expression is Delta-only, but the bug is 
Gluten's accounting, no Velox change needed for this step. Counting it natively 
(so MERGE's projection can go back to native) is the follow-up.
   
   @zhztheplayer @philo-he @felipepessoto @zhouyuan would appreciate a review 
on #13158 


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