Avoid deserialization when no columns are needed #16595
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This improves performance for count(const) or count(*) queris on formats that use GenericHiveRecordCursor.
electrum
approved these changes
Mar 17, 2023
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Note that as of now, all formats except Avro use the native Trino readers by default. @jklamer is working on Avro. |
raunaqmorarka
approved these changes
Mar 17, 2023
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Description
Even when no columns are accessed for a scan, GenericHiveRecordCursor pays the cost of deserializing the record - which is never used to get values out. This change avoids that deserialization and improves performance for count(const) or count(*) queries on formats that use GenericHiveRecordCursor.
Practically observed ~3x-4x improvement in CPU consumption for some queries.
We still need to fetch the data as long as we're dependent on RecordReader API since it doesn't provide a way to get counts.
Additional context and related issues
Test exists in
BaseHiveConnectorTest#testReadNoColumnsRelease notes
( ) This is not user-visible or docs only and no release notes are required.
( ) Release notes are required, please propose a release note for me.
( ) Release notes are required, with the following suggested text: