cloud: document Essential and Premium transaction limits#22905
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This pull request updates the documentation for TiDB Cloud Essential and Premium plans, clarifying that tidb_replica_read is read-only and Pipelined DML is unsupported. It also updates the default values for tidb_enable_assertion and pessimistic-auto-commit for these specific plans. Feedback focuses on improving clarity and consistency by using active voice, addressing users in the second person, and adopting template variables for plan names.
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| > **Note:** | ||
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| > For TiDB Cloud Essential and TiDB Cloud Premium, `tidb_replica_read` is read-only and fixed to `leader`. Other read modes are not supported. |
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Use active voice and template variables for plan names to maintain consistency with other documentation files in this repository. This also improves readability and simplifies future updates to plan names.
Suggested change
| > For TiDB Cloud Essential and TiDB Cloud Premium, `tidb_replica_read` is read-only and fixed to `leader`. Other read modes are not supported. | |
| > For [{{{ .essential }}}](https://docs.pingcap.com/tidbcloud/select-cluster-tier#essential) and [{{{ .premium }}}](https://docs.pingcap.com/tidbcloud/select-cluster-tier/#premium), `tidb_replica_read` is read-only and fixed to `leader`. These plans do not support other read modes. |
References
- Use consistent terminology and avoid passive voice overuse. (link)
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| > **Note:** | ||
| > | ||
| > Pipelined DML is not supported for TiDB Cloud Essential and TiDB Cloud Premium. You cannot enable Pipelined DML by setting [`tidb_dml_type`](/system-variables.md#tidb_dml_type-new-in-v800) to `"bulk"` or by using the [`SET_VAR`](/optimizer-hints.md#set_varvar_namevar_value) hint. |
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Use active voice and template variables for plan names to ensure consistency across the documentation set.
Suggested change
| > Pipelined DML is not supported for TiDB Cloud Essential and TiDB Cloud Premium. You cannot enable Pipelined DML by setting [`tidb_dml_type`](/system-variables.md#tidb_dml_type-new-in-v800) to `"bulk"` or by using the [`SET_VAR`](/optimizer-hints.md#set_varvar_namevar_value) hint. | |
| > [{{{ .essential }}}](https://docs.pingcap.com/tidbcloud/select-cluster-tier#essential) and [{{{ .premium }}}](https://docs.pingcap.com/tidbcloud/select-cluster-tier/#premium) do not support Pipelined DML. You cannot enable Pipelined DML by setting [`tidb_dml_type`](/system-variables.md#tidb_dml_type-new-in-v800) to `"bulk"` or by using the [`SET_VAR`](/optimizer-hints.md#set_varvar_namevar_value) hint. |
References
- Use consistent terminology and prefer active voice. (link)
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| > **Note:** | ||
| > | ||
| > This variable is read-only for [{{{ .essential }}}](https://docs.pingcap.com/tidbcloud/select-cluster-tier#essential) and [{{{ .premium }}}](https://docs.pingcap.com/tidbcloud/select-cluster-tier/#premium). The value is fixed to `"standard"`, so Pipelined DML cannot be enabled by setting this variable to `"bulk"`. |
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Use active voice to address the user directly, which makes the instruction clearer.
Suggested change
| > This variable is read-only for [{{{ .essential }}}](https://docs.pingcap.com/tidbcloud/select-cluster-tier#essential) and [{{{ .premium }}}](https://docs.pingcap.com/tidbcloud/select-cluster-tier/#premium). The value is fixed to `"standard"`, so Pipelined DML cannot be enabled by setting this variable to `"bulk"`. | |
| > This variable is read-only for [{{{ .essential }}}](https://docs.pingcap.com/tidbcloud/select-cluster-tier#essential) and [{{{ .premium }}}](https://docs.pingcap.com/tidbcloud/select-cluster-tier/#premium). The value is fixed to `"standard"`, so you cannot enable Pipelined DML by setting this variable to `"bulk"`. |
References
- Prefer active voice and address users in the second person. (link)
| > **Note:** | ||
| > | ||
| > This variable is read-only for [{{{ .premium }}}](https://docs.pingcap.com/tidbcloud/select-cluster-tier/#premium). | ||
| > This variable is read-only for [{{{ .essential }}}](https://docs.pingcap.com/tidbcloud/select-cluster-tier#essential) and [{{{ .premium }}}](https://docs.pingcap.com/tidbcloud/select-cluster-tier/#premium). The value is fixed to `leader`, and other read modes are not supported. |
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Use active voice to improve clarity and follow the general writing principles.
Suggested change
| > This variable is read-only for [{{{ .essential }}}](https://docs.pingcap.com/tidbcloud/select-cluster-tier#essential) and [{{{ .premium }}}](https://docs.pingcap.com/tidbcloud/select-cluster-tier/#premium). The value is fixed to `leader`, and other read modes are not supported. | |
| > This variable is read-only for [{{{ .essential }}}](https://docs.pingcap.com/tidbcloud/select-cluster-tier#essential) and [{{{ .premium }}}](https://docs.pingcap.com/tidbcloud/select-cluster-tier/#premium). The value is fixed to `leader`, and these plans do not support other read modes. |
References
- Avoid passive voice overuse. (link)
| + For scenarios with no conflicts, if there are many auto-commit transactions (the specific number is determined by the real scenarios. For example, the number of auto-commit transactions accounts for more than half of the total number of applications), and a single transaction operates a large data volume, enabling this configuration causes performance regression. For example, the auto-commit `INSERT INTO SELECT` statement. | ||
| + When the session-level system variable [`tidb_dml_type`](/system-variables.md#tidb_dml_type-new-in-v800) is set to `"bulk"`, the effect of this configuration in the session is equivalent to setting it to `false`. | ||
| + Default value: `false` | ||
| + Default value: `true` for [TiDB Cloud Essential](https://docs.pingcap.com/tidbcloud/select-cluster-tier#essential) and [TiDB Cloud Premium](https://docs.pingcap.com/tidbcloud/select-cluster-tier/#premium); `false` for other deployment options |
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Use template variables for plan names to maintain consistency with other documentation files and facilitate easier updates.
Suggested change
| + Default value: `true` for [TiDB Cloud Essential](https://docs.pingcap.com/tidbcloud/select-cluster-tier#essential) and [TiDB Cloud Premium](https://docs.pingcap.com/tidbcloud/select-cluster-tier/#premium); `false` for other deployment options | |
| + Default value: `true` for [{{{ .essential }}}](https://docs.pingcap.com/tidbcloud/select-cluster-tier#essential) and [{{{ .premium }}}](https://docs.pingcap.com/tidbcloud/select-cluster-tier/#premium); `false` for other deployment options |
References
- Use consistent terminology. (link)
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Pull request overview
This PR documents TiDB Cloud Essential and Premium limitations/defaults for transaction-related variables and feature behavior.
Changes:
- Adds Cloud-specific defaults for
pessimistic-auto-commitandtidb_txn_assertion_level. - Updates
tidb_dml_typeandtidb_replica_readnotes for Starter, Essential, and Premium plans. - Adds plan-specific notes to Pipelined DML and Follower Read docs.
Reviewed changes
Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.
| File | Description |
|---|---|
tidb-configuration-file.md |
Documents Cloud-specific default for pessimistic-auto-commit. |
system-variables.md |
Updates Cloud plan notes and defaults for transaction/read-related system variables. |
pipelined-dml.md |
Adds Essential/Premium unsupported note for Pipelined DML. |
follower-read.md |
Adds Essential/Premium fixed tidb_replica_read=leader note. |
💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.
| - Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): No | ||
| - Type: Enumeration | ||
| - Default value: `FAST` | ||
| - Default value: `STRICT` for [{{{ .essential }}}](https://docs.pingcap.com/tidbcloud/select-cluster-tier#essential) and [{{{ .premium }}}](https://docs.pingcap.com/tidbcloud/select-cluster-tier/#premium); `FAST` for other deployment options |
| + For scenarios with no conflicts, if there are many auto-commit transactions (the specific number is determined by the real scenarios. For example, the number of auto-commit transactions accounts for more than half of the total number of applications), and a single transaction operates a large data volume, enabling this configuration causes performance regression. For example, the auto-commit `INSERT INTO SELECT` statement. | ||
| + When the session-level system variable [`tidb_dml_type`](/system-variables.md#tidb_dml_type-new-in-v800) is set to `"bulk"`, the effect of this configuration in the session is equivalent to setting it to `false`. | ||
| + Default value: `false` | ||
| + Default value: `true` for [TiDB Cloud Essential](https://docs.pingcap.com/tidbcloud/select-cluster-tier#essential) and [TiDB Cloud Premium](https://docs.pingcap.com/tidbcloud/select-cluster-tier/#premium); `false` for other deployment options |
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| > **Note:** | ||
| > | ||
| > For TiDB Cloud Essential and TiDB Cloud Premium, `tidb_replica_read` is read-only and fixed to `leader`. Other read modes are not supported. |
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| > **Note:** | ||
| > | ||
| > Pipelined DML is not supported for TiDB Cloud Essential and TiDB Cloud Premium. You cannot enable Pipelined DML by setting [`tidb_dml_type`](/system-variables.md#tidb_dml_type-new-in-v800) to `"bulk"` or by using the [`SET_VAR`](/optimizer-hints.md#set_varvar_namevar_value) hint. |
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What is changed, added or deleted? (Required)
Document TiDB Cloud Essential and TiDB Cloud Premium behavior differences for transaction-related variables and configuration:
tidb_dml_typeis fixed to"standard", so Pipelined DML cannot be enabled by setting it to"bulk".tidb_replica_readis fixed toleader, and other read modes are not supported.tidb_txn_assertion_leveldefaults toSTRICT.pessimistic-auto-commitdefaults totrue.Which TiDB version(s) do your changes apply to? (Required)
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Do your changes match any of the following descriptions?