Julian Hyde created CALCITE-4986:
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Summary: Make HepProgram thread-safe
Key: CALCITE-4986
URL: https://issues.apache.org/jira/browse/CALCITE-4986
Project: Calcite
Issue Type: Bug
Reporter: Julian Hyde
{{HepProgram}} uses mutable fields for its working state and is therefore not
thread-safe. If two threads are planning queries simultaneously and are using
the same {{HepProgram}} instances they might conflict with each other. I
suspect that this happens several times in Calcite's standard set of rules.
This change would move the mutable state out of {{HepProgram}}, so that
{{HepProgram}} is fully immutable and therefore thread-safe.
It would also modernize some of the internals; for instance, {{class
HepInstruction.MatchLimit}} has a field {{int limit}} that could be made final
and assigned in the constructor.
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