[jira] [Commented] (CALCITE-3786) Add Digest interface to enable efficient hashCode(equals) for RexNode and RelNode

["Haisheng Yuan (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CALCITE-3786?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17129415#comment-17129415 ] 

Haisheng Yuan commented on CALCITE-3786:
----------------------------------------

I noticed Danny opened a pull request, thanks for taking this, Danny!

But frankly speaking, I am still against this idea, digest should not be used at all. The reason remains unchanged.

> 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
>
> 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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