[GitHub] [druid] jihoonson commented on pull request #10401: vectorized expressions and expression virtual columns

[GitBox <gi...@apache.org>]

jihoonson commented on pull request #10401:
URL: https://github.com/apache/druid/pull/10401#issuecomment-698015060


   Leaving a comment before I forget.. I tagged this PR with "Release Notes" as the vectorized operation can lead to a different query result when it computes floats and doubles. For example, in `DoubleSumVectorAggregator`, it first computes the `sum` of the given vector and then adds it to the accumulated sum in the buffer, while `DoubleSumBufferAggregator` keeps updating the accumulated sum directly. This change is not strictly caused in this PR (actually the issue was introduced in https://github.com/apache/druid/pull/6794), but I guess people will likely see this issue more often, since now SQL expressions can be vectorized. Perhaps we should update all release notes to call out this issue since 0.16.


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