executor: add placement policy name / direct placement to is.tables/partitions

[mjonss]

What problem does this PR solve?

Related to #18030 and #26681.

Problem Summary:
Missing ways to get placement from tables and partitions in an easy way or machine readable.
I added two new columns to both information_schema.tables and information_schema.partitions:
TIDB_PLACEMENT_POLICY_NAME and TIDB_DIRECT_PLACEMENT, which are NULLable varchar.

TIDB_PLACEMENT_POLICY_NAME refers to the named placement policy, and can be expanded either with SHOW PLACEMENT FOR POLICY <policy name> or through information_schema.placement_rules (like SELECT * FROM information_schema.tables t left join information_schema.placement_rules pr on t.TIDB_PLACEMENT_POLICY_NAME = pr.POLICY_NAME WHERE t.TABLE_NAME = 't'

What is changed and how it works?

What's Changed:
Two new columns in is.tables and is.partitions

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility - New columns in is.tables and is.partitions

Release note

Added TIDB_PLACEMENT_POLICY_NAME and TIDB_DIRECT_PLACEMENT columns to information_schema tables `tables` and `partitions`

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• morgo
• xhebox

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[djshow832]

Please add some test cases.

[morgo]

/run-check_title

[morgo]

I like it. Please add tests :-)

[xhebox]

I like it. Please add tests :-)

Do we need to record it in the RFC?

[morgo]

Do we need to record it in the RFC?

I will update it in another PR.

[morgo]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: eee83f7

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