Stamatis Zampetakis created HIVE-27831:
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Summary: Set hive.cbo.fallback.strategy to NEVER by default
Key: HIVE-27831
URL: https://issues.apache.org/jira/browse/HIVE-27831
Project: Hive
Issue Type: Task
Components: CBO
Reporter: Stamatis Zampetakis
Assignee: Stamatis Zampetakis
The hive.cbo.fallback.strategy property defines when Hive fallbacks to legacy
optimizer if an error occurs during the CBO phase.
At the moment the default value is CONSERVATIVE, which is the backward
compatible option, and automatically fallbacks to legacy optimizer when certain
errors occur.
The legacy optimizer is (hive.cbo.enable=false) is gonna soon be officially
deprecated (HIVE-27830); unofficially it was treated as such for a long time
now.
To reduce maintenance cost and improve CBO coverage and stability we should
NEVER fallback to the legacy optimizer after a CBO error.
NEVER should be the default behavior in newer releases; users can still set the
property to CONSERVATIVE as a temporary workaround till the CBO error is
addressed.
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