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system-variables: improve restricted-read-only docs (#8401) #8406

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May 9, 2022
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system-variables: improve restricted-read-only docs (#8401) #8406

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system-variables: improve restricted-read-only docs
morgo Apr 28, 2022
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Update system-variables.md
TomShawn May 9, 2022
d2a004a
Update system-variables.md
TomShawn May 9, 2022
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5 changes: 2 additions & 3 deletions system-variables.md
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Expand Up @@ -1551,9 +1551,8 @@ SET tidb_query_log_max_len = 20
### tidb_restricted_read_only <span class="version-mark">New in v5.2.0</span>

- Scope: GLOBAL
- Default value: `0`
- Value options: `0`, `1`
- This variable controls the read-only status of the entire cluster. If the variable is enabled (which means that the value is `1`), all TiDB servers in the entire cluster are in the read-only mode. In this case, TiDB only executes the statements that do not modify data, such as `SELECT`, `USE`, and `SHOW`. For other statements such as `INSERT` and `UPDATE`, TiDB rejects executing those statements in the read-only mode.
- Default value: `OFF`
- This variable controls the read-only status of the entire cluster. When the variable is `ON`, all TiDB servers in the entire cluster are in the read-only mode. In this case, TiDB only executes the statements that do not modify data, such as `SELECT`, `USE`, and `SHOW`. For other statements such as `INSERT` and `UPDATE`, TiDB rejects executing those statements in the read-only mode.
- Enabling the read-only mode using this variable only ensures that the entire cluster finally enters the read-only status. If you have changed the value of this variable in a TiDB cluster but the change has not yet propagated to other TiDB servers, the un-updated TiDB servers are still **not** in the read-only mode.
- When this variable is enabled, the SQL statements being executed are not affected. TiDB only performs the read-only check for the SQL statements **to be** executed.
- When this variable is enabled, TiDB handles the uncommitted transactions in the following ways:
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