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update TTL doc to allow split tasks for utf8 column #18713

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Oct 16, 2024
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update TTL doc to allow split tasks for utf8 column #18713

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update TTL doc to allow split tasks for utf8 colum
lcwangchao Aug 27, 2024
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hfxsd Sep 6, 2024
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hfxsd Sep 10, 2024
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Update time-to-live.md
lcwangchao Sep 14, 2024
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lcwangchao Sep 14, 2024
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11 changes: 10 additions & 1 deletion time-to-live.md
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Expand Up @@ -257,7 +257,16 @@
* The TTL attribute cannot be set on temporary tables, including local temporary tables and global temporary tables.
* A table with the TTL attribute does not support being referenced by other tables as the primary table in a foreign key constraint.
* It is not guaranteed that all expired data is deleted immediately. The time when expired data is deleted depends on the scheduling interval and scheduling window of the background cleanup job.
* For tables that use [clustered indexes](/clustered-indexes.md), if the primary key is neither an integer nor a binary string type, the TTL job cannot be split into multiple tasks. This will cause the TTL job to be executed sequentially on a single TiDB node. If the table contains a large amount of data, the execution of the TTL job might become slow.
* For tables that use [clustered indexes](/clustered-indexes.md), a TTL job can be split into multiple subtasks only in the following scenarios:
- The first column of the primary key or composite primary key is of `INTEGER` or binary string types. The binary string types mainly refer to the following:
- `CHAR(N) CHARACTER SET BINARY`
- `VARCHAR(N) CHARACTER SET BINARY`
- `BINARY(N)`
- `VARBINARY(N)`
- `BIT(N)`
- The character set of the first column of the primary key or composite primary key is `utf8` or `utf8mb4` and the collate is `utf8_bin`, `utf8mb4_bin` or `utf8mb4_0900_bin`.
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- For tables where the primary key column type is `utf8` or `utf8mb4`, subtasks are split only based on the range of visible ASCII characters. If many primary key values have the same ASCII prefix, it might cause uneven task splitting.

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[PingCAP.Ambiguous] Consider using a clearer word than 'many' because it may cause confusion.

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{"message": "[PingCAP.Ambiguous] Consider using a clearer word than 'many' because it may cause confusion.", "location": {"path": "time-to-live.md", "range": {"start": {"line": 268, "column": 151}}}, "severity": "INFO"}
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- For tables that do not support splitting a TTL job into multiple subtasks, the TTL job will be executed sequentially on a single TiDB node. If the table contains a large amount of data, the execution of the TTL job might become slow.

## FAQs

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