information_schema: Update IS_VISIBLE description

[dveeden]

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Hello @dveeden, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

Summary of Changes

This pull request updates the description of the IS_VISIBLE field in the STATISTICS table of the information_schema. The change clarifies that IS_VISIBLE indicates whether an index is visible or not, and it provides a reference to the documentation on invisible indexes. The PR affects versions master, v9.0, and v8.5.

Highlights

• Documentation update: The description of the IS_VISIBLE field in the STATISTICS table is updated to improve clarity.
• Invisible index reference: A link to the documentation on invisible indexes is added to the IS_VISIBLE field description.

Changelog

• information-schema/information-schema-statistics.md
  • Updated the description of the IS_VISIBLE field to clarify its meaning.
  • Added a reference to the documentation on invisible indexes.

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Code Review

The pull request updates the description of the IS_VISIBLE field in the STATISTICS table of the information schema to clarify its meaning and provide a reference to the invisible index feature. This is a good change that improves the documentation's clarity and accuracy.

Merge Readiness

The pull request is ready to be merged. The change is straightforward and improves the documentation. I am unable to approve the pull request, and users should have others review and approve this code before merging.

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[dveeden]

Example:

mysql-8.0.11-TiDB-v9.0.0-beta.1.pre-491-g446952c> CREATE TABLE t1 (id INT PRIMARY KEY, c1 INT, KEY(c1) INVISIBLE);
Query OK, 0 rows affected (0.05 sec)

mysql-8.0.11-TiDB-v9.0.0-beta.1.pre-491-g446952c> SELECT * FROM information_schema.STATISTICS WHERE TABLE_NAME='t1' AND TABLE_SCHEMA='test'\G
*************************** 1. row ***************************
TABLE_CATALOG: def
 TABLE_SCHEMA: test
   TABLE_NAME: t1
   NON_UNIQUE: 0
 INDEX_SCHEMA: test
   INDEX_NAME: PRIMARY
 SEQ_IN_INDEX: 1
  COLUMN_NAME: id
    COLLATION: A
  CARDINALITY: 0
     SUB_PART: NULL
       PACKED: NULL
     NULLABLE: 
   INDEX_TYPE: BTREE
      COMMENT: 
INDEX_COMMENT: 
   IS_VISIBLE: YES
   Expression: NULL
*************************** 2. row ***************************
TABLE_CATALOG: def
 TABLE_SCHEMA: test
   TABLE_NAME: t1
   NON_UNIQUE: 1
 INDEX_SCHEMA: test
   INDEX_NAME: c1
 SEQ_IN_INDEX: 1
  COLUMN_NAME: c1
    COLLATION: A
  CARDINALITY: 0
     SUB_PART: NULL
       PACKED: NULL
     NULLABLE: YES
   INDEX_TYPE: BTREE
      COMMENT: 
INDEX_COMMENT: 
   IS_VISIBLE: NO
   Expression: NULL
2 rows in set (0.00 sec)

Note that tidb_opt_use_invisible_indexes can make invisible indexes visible to the optimizer, which doesn't really match with the current description of IS_VISIBLE.