Zoltán Borók-Nagy created IMPALA-9228:
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Summary: ORC scanner could be vectorized
Key: IMPALA-9228
URL: https://issues.apache.org/jira/browse/IMPALA-9228
Project: IMPALA
Issue Type: Improvement
Reporter: Zoltán Borók-Nagy
The ORC scanners uses an external library to read ORC files. The library reads
the file contents into its own memory representation. It is a vectorized
representation similar to the Arrow format.
Impala needs to convert the ORC row batch to an Impala row batch. Currently the
conversion happens row-wise and column-by-column via a virtual function call:
[https://github.com/apache/impala/blob/85425b81f04c856d7d5ec375242303f78ec7964e/be/src/exec/hdfs-orc-scanner.cc#L671]
[https://github.com/apache/impala/blob/85425b81f04c856d7d5ec375242303f78ec7964e/be/src/exec/orc-column-readers.cc#L352]
Instead of this approach it could work similarly to the Parquet scanner that
fills the columns one-by-one into a scratch batch, then evaluate the conjuncts
on the scratch batch. For more details see HdfsParquetScanner::AssembleRows():
[https://github.com/apache/impala/blob/85425b81f04c856d7d5ec375242303f78ec7964e/be/src/exec/parquet/hdfs-parquet-scanner.cc#L1077-L1088]
This way we'll need a lot less virtual function calls, also the memory
reads/writes will be much more localized and predictable.
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