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cloud: add new limitations on TiDB serverless for 7.1 #15645

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cloud: Add new limitation on serverless
baiyuqing Dec 11, 2023
41c42cd
updete SEM doc
baiyuqing Dec 11, 2023
d0e2796
fix lint
baiyuqing Dec 11, 2023
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fix lint
baiyuqing Dec 11, 2023
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4 changes: 4 additions & 0 deletions system-variables.md
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Expand Up @@ -4150,6 +4150,10 @@ SHOW WARNINGS;

### tidb_replica_read <span class="version-mark">New in v4.0</span>

>**Note:**
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It's nice to have this note as cross reference.

Unfortunately, all the rest variables and statements did not have this. We should add them all or none.

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Agreed.

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@qiancai qiancai Feb 23, 2024 •
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If you search TiDB Serverless on https://docs.pingcap.com/tidb/dev/system-variables, you'll find there are more than 60 instances that indicate the TiDB Serverless support info.

For example:
image

Therefore, it looks OK to add the support info for this variable too.

>
>This variable is not supported on [TiDB Serverless](https://docs.pingcap.com/tidbcloud/select-cluster-tier#tidb-serverless).

- Scope: SESSION | GLOBAL
- Persists to cluster: Yes
- Type: Enumeration
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15 changes: 14 additions & 1 deletion tidb-cloud/limited-sql-features.md
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Expand Up @@ -223,12 +223,23 @@ TiDB Cloud works with almost all workloads that TiDB supports, but there are som
| `validate_password.policy` | No limitation | Can only be `MEDIUM` or `STRONG` [^10] |
| `validate_password.special_char_count` | No limitation | At least `1` [^10] |
| `wait_timeout` | No limitation | Read-only [^11] |
| `tidb_replica_read` | No limitation | Read-only [^14] |

## Optimizer Hint

| Hint | TiDB Dedicated | TiDB Serverless |
|:-|:-|:-|
| `RESOURCE_GROUP()` | No limitation | Not supported |
| `RESOURCE_GROUP()` | No limitation | Not supported |
| `MEMORY_QUOTA()` | No limitation | Not supported |
| `MAX_EXECUTION_TIME()` | No limitation | Not supported |
| `READ_CONSISTENT_REPLICA()` | No limitation | Not supported [^14] |

[^1]: Configuring data placement is not supported on TiDB Serverless.

[^2]: Configuring resource groups is not supported on TiDB Serverless.

[^3]: To perform [Back up and Restore](/tidb-cloud/backup-and-restore-serverless.md) operations on TiDB Serverless, you can use the TiDB Cloud console instead.
[^3]: To perform [Back up and Restore](/tidb-cloud/backup-and-restore-serverless.md) operations on TiDB Serverless, you can use the TiDB Cloud console instead.

[^4]: The feature is unavailable in [Security Enhanced Mode (SEM)](/system-variables.md#tidb_enable_enhanced_security).

Expand All @@ -249,3 +260,5 @@ TiDB Cloud works with almost all workloads that TiDB supports, but there are som
[^12]: Customizing cache size using [`AUTO_ID_CACHE`](/auto-increment.md#cache-size-control) is temporarily unavailable on TiDB Serverless.

[^13]: Not supported. Enabling `require_secure_transport` for TiDB Dedicated clusters will result in SQL client connection failures.

[^14]: `tidb_replica_read` only supports `leader` on TiDB Serverless.