Frank Chen created CALCITE-7809:
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Summary: Avoid copying unchanged SQL and Rex operands
Key: CALCITE-7809
URL: https://issues.apache.org/jira/browse/CALCITE-7809
Project: Calcite
Issue Type: Sub-task
Reporter: Frank Chen
RexShuttle and SqlShuttle visit every child and return either the original
child or a replacement. They currently copy operand collections before knowing
whether any child changes, then discard those copies when the traversal is
read-only.
Make these operand collections copy-on-write. Allocate only when the first
changed child is encountered, while preserving RexShuttle's immutable-result
contract and SqlShuttle's explicit alwaysCopy behavior.
The isolated Druid benchmark reduced allocation by 2.72% at 100,000 string
literals and 1.55% at 1,000,000 string literals.
Pull request: [PR #5283|https://github.com/apache/calcite/pull/5283]
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