[jira] [Created] (CALCITE-3786) Add Digest (HashStrategy?) interface to enable efficient hashCode/equals for RexNode, RelNode

["Vladimir Sitnikov (Jira)" <ji...@apache.org>]

Vladimir Sitnikov created CALCITE-3786:
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             Summary: 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


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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