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https://issues.apache.org/jira/browse/CALCITE-3786?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17137805#comment-17137805
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Laurent Goujon commented on CALCITE-3786:
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{quote}
Laurent Goujon It seems that you have some promotion ideas for the Digest code,
feel free to do that, i tried to answer each message you left in the PR, hope
it helps. But i would not revert the PR for no other strong reason, sorry.
{quote}
The thing is that you left no time to answer back (sorry, I'm not working over
the weekend), or did you send a courtesy check on either the pull request and
the jira issue to see people got their questions answers/concerns alleviated.
We usually try to reach a consensus on issues and code changes, but it doesn't
seem to be the case here. And it's a bit disappointed you are not ready to
revert temporarily your change unless there are strong reason whereas (ignoring
my comments/concerns on github) the lack of concrete evaluation regarding
memory usage and performance impact seems quite a strong reason to do so...
> Add Digest interface to enable efficient hashCode(equals) for RexNode and
> 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
> Assignee: Danny Chen
> Priority: Major
> Fix For: 1.24.0
>
> Time Spent: 5h 20m
> Remaining Estimate: 0h
>
> 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".
> A 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
> String toString(); // e.g. for debugging purposes
> int compareTo(Digest); // e.g. for debugging purposes.
> }
> {code}
> Note how fields in Kotlin are aligned much better, and it makes it easier to
> read:
> {code:java}
> class Digest { // immutable
> val hashCode: Int // speedup hashCode and equals
> val contents: Array<Any> // The values are either other Digest objects or
> Strings
> fun toString(): String // e.g. for debugging purposes
> fun compareTo(other: Digest): Int // e.g. for debugging purposes.
> }
> {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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