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https://issues.apache.org/jira/browse/CALCITE-3167?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16877833#comment-16877833
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jin xing commented on CALCITE-3167:
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Thanks a lot for reply [~julianhyde]
# I also think it's a good idea to prohibit overriding {{equals}} and
{{hashCode}} for {{RelNode}} and users should define the identity case by case;
# As for overriding {{equals}} and {{hashCode}} in {{AbstractRelNode}} and
making them final, how about implement by {{digest ?}} i.e. {{RelNodes equals
with each other when they have the same}} {{digests}} and we generate
{{hashCode}} of {{RelNode}} by {{digest}}'s {{hashCode}}. User should guarantee
that all key information should be included in {{digest}}
# I think the idea in CALCITE-1216 is straightforward. Before that change,
'materialization-substitution' only happens at the very start of
{{findBestExp}}. After the change, {{MaterializedViewFilterScanRule.java does}}
the materialization-substitution during running optimization-rules. Thus query
plan has a chance to be 'normalized' after some optimization rules and then
get optimized by materialization-substitution. This might introduce extra cost
since the materialization-substitution tends to be a heavy process.
# Digging the code, I did't find any necessity for the {{overrides}} in
{{EnumerableScan}}. After removing them, I passed all the tests. I think
existing tests are sufficient. Because {{EnumerableTableScanRule}} will create
a new EnumerableTableScan every time it meets a LogicalTableScan, i.e.
{{query}} and {{materialization}} don't share the same Java object for
table-scan.
> Remove overriding equals and hashCode methods in EnumerableTableScan
> --------------------------------------------------------------------
>
> Key: CALCITE-3167
> URL: https://issues.apache.org/jira/browse/CALCITE-3167
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Affects Versions: 1.19.0
> Reporter: jin xing
> Priority: Minor
> Labels: pull-request-available
> Time Spent: 20m
> Remaining Estimate: 0h
>
> In current code of {{EnumerableTableScan}}, methods of equals and hashCode
> are overridden for matching of {{EnumerableTableScan}}s.
> While after optimizing with the same HEP planner, {{EnumerableTableScan}}s
> from two plans but with the same digest will the share the same Java object.
> See
> [RelOptMaterializations|https://github.com/apache/calcite/blob/adf4cc4dc5cdb9f5e49c85d10f46a2fdcd831ccf/core/src/main/java/org/apache/calcite/plan/RelOptMaterializations.java#L192].
> I think it's ok to remove the redundant overriding methods in
> {{EnumerableTableScan}}.
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