pendingData linked list in Llap IO elevator (LlapRecordReader.java) may grow indefinitely when Llap IO is faster than processing pipeline. Since we don't have backpressure to slow down the IO, this can lead to indefinite growth of pending data leading to severe GC pressure and eventually lead to OOM.
This specific instance of LLAP was running on HDFS on top of EBS volume backed by SSD. The query that triggered this is issue was ANALYZE STATISTICS .. FOR COLUMNS which also gather bitvectors. Fast IO and Slow processing case.