Feng Jin created FLINK-33996:
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Summary: Support disabling project rewrite when multiple exprs in
the project reference the same project.
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
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.FlinkProjectMergeRule
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