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https://issues.apache.org/jira/browse/CALCITE-3786?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17035616#comment-17035616
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Rui Wang commented on CALCITE-3786:
-----------------------------------
Maybe need to exclude some classes. E.g RexLiteral and RexInputRef which can
compare their member variables directly.
> Add Digest (HashStrategy?) interface to enable efficient hashCode/equals for
> RexNode, RelNode
> ---------------------------------------------------------------------------------------------
>
> Key: CALCITE-3786
> URL: https://issues.apache.org/jira/browse/CALCITE-3786
> Project: Calcite
> Issue Type: New Feature
> Components: core
> Affects Versions: 1.21.0
> Reporter: Vladimir Sitnikov
> Priority: Major
>
> Current digests for RexNode, RelNode, RelType, and similar cases use String
> concatenation.
> It is easy to implement, however, it has drawbacks:
> 1) String objects cannot be reused. For instance, RexCall has operands,
> however, the digest is duplicated. It causes extra memory use, and extra CPU
> for string copying
> 2) There's no way to have multiple #toString() methods. RelType might need
> multiple digests: "including field names", "excluding field names".
> Suggested resolution might be behind the lines of
> {code:java}
> class Digest { // immutable
> final int hashCode; // speedup hashCode and equals
> final Object[] contents; // The values are either other Digest objects or
> Strings
> }
> {code}
> Then the digest for RexCall could be the bits relevant to RexCall itself +
> digests of the operands (which can be reused as is)
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