Github user chunhui-shi commented on the issue: https://github.com/apache/drill/pull/638 The performance degradation is worse with larger tables. The degradation is >300% on a 15GB table. After this fix, this degradation disappears. There are other visible performance gains of this fix even when there is no degradation: For a simple query on ORC/Parquet table through HiveReaders, I observed the improvement is about 10%-25% and the average improved percentage is 17.6%. For TPCH tests on a 10 node cluster with Parquet tables + HiveReaders, the average improvement (of two runs) is 5.1%
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