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https://issues.apache.org/jira/browse/CALCITE-3786?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17133205#comment-17133205
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Vladimir Sitnikov commented on CALCITE-3786:
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>so that we can finally compare 2 RexCall using member equals, and it works
>well.
1) There are code parts that still use #toString() for the comparison (e.g.
RexSimplify)
2) I had exactly that suggestion (normalize RexNodes on creation), however, you
have cast -1 multiple times because that would alter string representation of
the plans with little gain.
[https://lists.apache.org/thread.html/d89103671efdd813fac768fbc2336bd125e925f0790e9137a2a16375%40%3Cdev.calcite.apache.org%3E]
My suggestion was
Vladimir: It turned out "b" (sort operands in computeDigest) is easier to
implement.
Vladimir: I've filed a PR: [https://github.com/apache/calcite/pull/1703
]
and your response was "I’m strongly -1 for this way, because it beaks the plan
test where almost all of the change are meaningless."
Note: PR1703 was updated since that discussion, and the actual implementation
normalizes nodes at the planning time only, while the user-visible plans are
displayed without normalization.
> 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
> Time Spent: 50m
> 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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