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ti-chi-bot merged 4 commits into from
Sep 28, 2022
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add 6 system variables introduced in 6.3 but have no user doc #10564

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add 6 system variables introduced in 6.3 but have no user doc
shichun-0415 Sep 27, 2022
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shichun-0415 Sep 27, 2022
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shichun-0415 Sep 28, 2022
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64 changes: 64 additions & 0 deletions system-variables.md
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Expand Up @@ -909,6 +909,18 @@ MPP is a distributed computing framework provided by the TiFlash engine, which a
- Range: `[0, 9223372036854775807]`
- This variable is used to set the number of retries when the DDL operation fails. When the number of retries exceeds the parameter value, the wrong DDL operation is canceled.

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### `tidb_ddl_flashback_concurrency` <span class="version-mark">New in v6.3.0</span>

> **Warning:**
>
> The feature controlled by this variable is not fully functional in the current TiDB version. Do not change the default value.

- Scope: GLOBAL
- Persists to cluster: Yes
- Default value: `64`
- Range: `[1, 256]`
- This variable controls the concurrency of `flashback cluster`.

### tidb_ddl_reorg_batch_size

- Scope: GLOBAL
Expand Down Expand Up @@ -1211,6 +1223,28 @@ MPP is a distributed computing framework provided by the TiFlash engine, which a
- This variable is used to set whether to enable the statistics `Fast Analyze` feature.
- If the statistics `Fast Analyze` feature is enabled, TiDB randomly samples about 10,000 rows of data as statistics. When the data is distributed unevenly or the data size is small, the statistics accuracy is low. This might lead to a non-optimal execution plan, for example, selecting a wrong index. If the execution time of the regular `Analyze` statement is acceptable, it is recommended to disable the `Fast Analyze` feature.

### `tidb_enable_foreign_key` <span class="version-mark">New in v6.3.0</span>

> **Warning:**
>
> The feature controlled by this variable is not fully functional in the current TiDB version. Do not change the default value.

- Scope: GLOBAL
- Persists to cluster: Yes
- Default value: `OFF`
- This variable controls whether to enable the `FOREIGN KEY` feature.

### `tidb_enable_general_plan_cache` <span class="version-mark">New in v6.3.0</span>

> **Warning:**
>
> The feature controlled by this variable is not fully functional in the current TiDB version. Do not change the default value.

- Scope: SESSION | GLOBAL
- Persists to cluster: Yes
- Default value: `OFF`
- This variable controls whether to enable the General Plan Cache feature.

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

> **Note:**
Expand Down Expand Up @@ -1320,6 +1354,13 @@ MPP is a distributed computing framework provided by the TiFlash engine, which a
* When you use `SELECT` to read a `noop` variable, TiDB returns the `"variable *variable_name* has no effect in TiDB"` warning.
- To check whether a TiDB instance has set and read the `noop` variable, you can use the `SELECT * FROM INFORMATION_SCHEMA.CLIENT_ERRORS_SUMMARY_GLOBAL;` statement.

### `tidb_enable_null_aware_anti_join` <span class="version-mark">New in v6.3.0</span>

- Scope: SESSION ｜GLOBAL
- Persists to cluster: Yes
- Default value: `OFF`
- This variable controls whether TiDB applies Null Aware Hash Join when ANTI JOIN is generated by subqueries led by special set operators `NOT IN` and `!= ALL`.

### tidb_enable_outer_join_reorder <span class="version-mark">New in v6.1.0</span>

- Scope: SESSION | GLOBAL
Expand Down Expand Up @@ -1496,6 +1537,17 @@ Query OK, 0 rows affected (0.09 sec)

</CustomContent>

### `tidb_enable_tiflash_read_for_write_stmt` <span class="version-mark">New in v6.3.0</span>

> **Warning:**
>
> The feature controlled by this variable is not fully functional in the current TiDB version. Do not change the default value.

- Scope: SESSION | GLOBAL
- Persists to cluster: Yes
- Default value: `OFF`
- This variable controls whether read requests in SQL write statements can be pushed down to TiFlash.

### tidb_enable_top_sql <span class="version-mark">New in v5.4.0</span>

<CustomContent platform="tidb-cloud">
Expand Down Expand Up @@ -1814,6 +1866,18 @@ For a system upgraded to v5.0 from an earlier version, if you have not modified

</CustomContent>

### `tidb_general_plan_cache_size` <span class="version-mark">New in v6.3.0</span>

> **Warning:**
>
> The feature controlled by this variable is not fully functional in the current TiDB version. Do not change the default value.

- Scope: SESSION | GLOBAL
- Persists to cluster: Yes
- Default value: `100`
- Range: `[1, 100000]`
- This variable controls the maximum number of execution plans that can be cached by General Plan Cache.

### tidb_guarantee_linearizability <span class="version-mark">New in v5.0</span>

- Scope: SESSION | GLOBAL
Expand Down