[
https://issues.apache.org/jira/browse/FLINK-33996?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17803524#comment-17803524
]
Feng Jin commented on FLINK-33996:
----------------------------------
[~xuyangzhong] Introducing a new rule may be a better way, otherwise we would
need to modify multiple rules listed above.
> Support disabling project rewrite when multiple exprs in the project
> reference the same sub project field.
> ----------------------------------------------------------------------------------------------------------
>
> Key: FLINK-33996
> URL: https://issues.apache.org/jira/browse/FLINK-33996
> Project: Flink
> Issue Type: Improvement
> Components: Table SQL / Runtime
> Affects Versions: 1.18.0
> Reporter: Feng Jin
> Priority: Major
>
> When multiple top projects reference the same bottom project, project rewrite
> rules may result in complex projects being calculated multiple times.
> Take the following SQL as an example:
> {code:sql}
> create table test_source(a varchar) with ('connector'='datagen');
> explan plan for select a || 'a' as a, a || 'b' as b FROM (select
> REGEXP_REPLACE(a, 'aaa', 'bbb') as a FROM test_source);
> {code}
> The final SQL plan is as follows:
> {code:sql}
> == Abstract Syntax Tree ==
> LogicalProject(a=[||($0, _UTF-16LE'a')], b=[||($0, _UTF-16LE'b')])
> +- LogicalProject(a=[REGEXP_REPLACE($0, _UTF-16LE'aaa', _UTF-16LE'bbb')])
> +- LogicalTableScan(table=[[default_catalog, default_database,
> test_source]])
> == Optimized Physical Plan ==
> Calc(select=[||(REGEXP_REPLACE(a, _UTF-16LE'aaa', _UTF-16LE'bbb'),
> _UTF-16LE'a') AS a, ||(REGEXP_REPLACE(a, _UTF-16LE'aaa', _UTF-16LE'bbb'),
> _UTF-16LE'b') AS b])
> +- TableSourceScan(table=[[default_catalog, default_database, test_source]],
> fields=[a])
> == Optimized Execution Plan ==
> Calc(select=[||(REGEXP_REPLACE(a, 'aaa', 'bbb'), 'a') AS a,
> ||(REGEXP_REPLACE(a, 'aaa', 'bbb'), 'b') AS b])
> +- TableSourceScan(table=[[default_catalog, default_database, test_source]],
> fields=[a])
> {code}
> It can be observed that after project write, regex_place is calculated twice.
> Generally speaking, regular expression matching is a time-consuming operation
> and we usually do not want it to be calculated multiple times. Therefore, for
> this scenario, we can support disabling project rewrite.
> After disabling some rules, the final plan we obtained is as follows:
> {code:sql}
> == Abstract Syntax Tree ==
> LogicalProject(a=[||($0, _UTF-16LE'a')], b=[||($0, _UTF-16LE'b')])
> +- LogicalProject(a=[REGEXP_REPLACE($0, _UTF-16LE'aaa', _UTF-16LE'bbb')])
> +- LogicalTableScan(table=[[default_catalog, default_database,
> test_source]])
> == Optimized Physical Plan ==
> Calc(select=[||(a, _UTF-16LE'a') AS a, ||(a, _UTF-16LE'b') AS b])
> +- Calc(select=[REGEXP_REPLACE(a, _UTF-16LE'aaa', _UTF-16LE'bbb') AS a])
> +- TableSourceScan(table=[[default_catalog, default_database,
> test_source]], fields=[a])
> == Optimized Execution Plan ==
> Calc(select=[||(a, 'a') AS a, ||(a, 'b') AS b])
> +- Calc(select=[REGEXP_REPLACE(a, 'aaa', 'bbb') AS a])
> +- TableSourceScan(table=[[default_catalog, default_database,
> test_source]], fields=[a])
> {code}
> After testing, we probably need to modify these few rules:
> org.apache.flink.table.planner.plan.rules.logical.FlinkProjectMergeRule
> org.apache.flink.table.planner.plan.rules.logical.FlinkCalcMergeRule
> org.apache.flink.table.planner.plan.rules.logical.FlinkProjectCalcMergeRule
--
This message was sent by Atlassian Jira
(v8.20.10#820010)
