docs/design: add proposal for invisible index #15338
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wjhuang2016
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Mar 12, 2020
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| MySQL supports [Invisible indexes](https://dev.mysql.com/doc/refman/8.0/en/invisible-indexes.html); that is, indexes that are not used by the optimizer. | ||
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| This is a useful feature when you want to drop an index in a safe way. Invisible indexes make it possible to test the effect of removing an index on query performance, without making a destructive change that must be undone should the index turn out to be required. Dropping and re-adding an index can be expensive for a large table, whereas making it invisible and visible are fast, in-place operations. |
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should the index turn out to be required ?
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This statement is copied from mysql docs, translating into Chinese:
不可见的索引可以测试移除索引对查询性能的影响，而不会做出破坏性的更改，如果（移除后）发现索引是必需的，则必须撤销这些更改。
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@wjhuang2016, PTAL. |
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@wjhuang2016, @AilinKid, PTAL. |
Deardrops
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status/LGT2
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@bb7133 This PR is ready for merge, PTAL |
wjhuang2016
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status/can-merge
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/run-all-tests |
ngaut
approved these changes
Mar 18, 2020
bb7133
reviewed
Mar 18, 2020
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| ## Abstract | ||
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| MySQL supports [Invisible indexes](https://dev.mysql.com/doc/refman/8.0/en/invisible-indexes.html); that is, indexes that are not used by the optimizer. |
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Suggested change
| MySQL supports [Invisible indexes](https://dev.mysql.com/doc/refman/8.0/en/invisible-indexes.html); that is, indexes that are not used by the optimizer. | |
| MySQL supports [invisible indexes](https://dev.mysql.com/doc/refman/8.0/en/invisible-indexes.html); that is, indexes that are not used by the optimizer. |
| {VISIBLE | INVISIBLE} | ||
| ``` | ||
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| Also, consider the following: |
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Suggested change
| Also, consider the following: | |
| Also, the following behaviors need to be supported as well: |
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| ## Proposal | ||
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| Adding an option (visible or not) to the index. If it is not visible, it's called **Invisible Index**. Invisible Index cannot be used by the optimizer (with the `use_invisible_indexes` switch on), but the index is maintained during DML operations. For a query statement, invisible index has the same effect as ignoring the index through Index Hint. |
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Suggested change
| Adding an option (visible or not) to the index. If it is not visible, it's called **Invisible Index**. Invisible Index cannot be used by the optimizer (with the `use_invisible_indexes` switch on), but the index is maintained during DML operations. For a query statement, invisible index has the same effect as ignoring the index through Index Hint. | |
| Adding an option (visible or not) to the index. If it is not visible, it's called **Invisible Index**. Invisible indexes cannot be used by the optimizer (with the `use_invisible_indexes` switch on), but the index is maintained during DML operations. For a query statement, invisible indexes have the same effect as ignoring the index through Index Hint. |
| ALTER TABLE table_name ALTER INDEX index_name { INVISIBLE | VISIBLE }; | ||
| ``` | ||
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| Or set option `INVISIBLE` when creating an index: |
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Suggested change
| Or set option `INVISIBLE` when creating an index: | |
| Or by setting option `INVISIBLE` when creating an index: |
| ## Compatibility and Migration Plan | ||
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| This the a new feature and it's absolutly compatible with old TiDB versions, also, it's not impact any data migration. | ||
| The syntax and functions are basically compatible with MySQL. Expect one: |
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Suggested change
| The syntax and functions are basically compatible with MySQL. Expect one: | |
| The syntax and functions are basically compatible with MySQL expect: |
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| ## Compatibility and Migration Plan | ||
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| This the a new feature and it's absolutly compatible with old TiDB versions, also, it's not impact any data migration. |
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Suggested change
| This the a new feature and it's absolutly compatible with old TiDB versions, also, it's not impact any data migration. | |
| This the a new feature and it's absolutly compatible with old TiDB versions, also, it does not impact any data migration. |
| The syntax and functions are basically compatible with MySQL. Expect one: | ||
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| When use invisible index in `SQL Hint`, and set `use_invisible_indexes = false`, MySQL allow use the invisible index. | ||
| But in TiDB, It's **not allowed**, and will throw a `Unresolved name` error, Because the behavior is more reasonable. |
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Suggested change
| But in TiDB, It's **not allowed**, and will throw a `Unresolved name` error, Because the behavior is more reasonable. | |
| But in TiDB, It's **not allowed** and an `Unresolved name` error will be thrown. |
| ## Testing Plan | ||
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| - Unit test | ||
| - Port All mysql test related to invisible index |
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Suggested change
| - Port All mysql test related to invisible index | |
| - Learn from MySQL test cases related to invisible indexes |
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What problem does this PR solve?
This PR adds a proposal for full invisible index support in TiDB.
An issue has been created for the discussions on this proposal:
#9246