system-variables: update from generated source #7737

morgo · 2022-03-02T23:39:29Z

What is changed, added or deleted? (Required)

This updates the system-variables docs, as generated by linking against the tidb source code. There are a lot of small edits, I will explain each in-line.

This only affects tidb-master safely. There might be some smaller updates which need to be cherry picked to 5.4.

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ti-chi-bot · 2022-03-02T23:39:31Z

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morgo · 2022-03-02T23:40:21Z

system-variables.md

-### placement_checks <span class="version-mark">New in v5.3.0</span>
-
- Scope: SESSION | GLOBAL
- Default value: `ON`
- This variable controls whether DDL statements validate [Placement Rules in SQL](/placement-rules-in-sql.md).
- It is intended to be used by logical dump/restore tools to ensure that tables can always be created even if placement rules are violated. This is similar to how mysqldump writes `SET FOREIGN_KEY_CHECKS=0;` to the start of every dump file.
-


This variable has been removed in TiDB 5.4. A new variable tidb_placement_mode exists instead (I will document it separately).

Is this change will be in 5.4.1? i checked in 5.4.0, 'placement_checks' still exist, and no 'tidb_placement_mode' in system variable list.

Here is the PR: pingcap/tidb#31093

It looks like it was created before 5.4 code freeze, but merged after. So my understanding was not correct - it is a 6.0 only change.

morgo · 2022-03-02T23:41:06Z

system-variables.md

- Scope: SESSION | GLOBAL
+- Scope: GLOBAL


This behavior change is intentional and only affects master. See: https://github.com/pingcap/tidb/blob/master/docs/design/2021-12-08-instance-scope.md

morgo · 2022-03-02T23:41:29Z

system-variables.md

-### tidb_enable_alter_placement
-
-> **Warning:**
->
-> Currently, Placement Rules in SQL is an experimental feature. It is not recommended that you use it in production environments.
-
- Scope: GLOBAL
- Default value: `OFF`
- This variable enables or disables [Placement Rules in SQL](/placement-rules-in-sql.md).
-


This is an experimental flag, but the feature is being declared stable in master.

morgo · 2022-03-02T23:42:09Z

system-variables.md

@@ -779,6 +758,10 @@ Constraint checking is always performed in place for pessimistic transactions (d
 >
 > - Since v5.4.0, for a newly deployed TiDB cluster, this variable is enabled by default.

+- Scope: SESSION | GLOBAL
+- Default value: `ON`
+- This variable is used to control whether to enable the index merge feature.


This just moves the comment above the feature specification, to be consistent. We generate it this way in every other case.

morgo · 2022-03-02T23:42:31Z

system-variables.md

- Scope: SESSION | GLOBAL
+- Scope: GLOBAL


This behavior change is intentional and only affects master. See: https://github.com/pingcap/tidb/blob/master/docs/design/2021-12-08-instance-scope.md

morgo · 2022-03-02T23:43:20Z

system-variables.md

+### tidb_enable_top_sql <span class="version-mark">New in v5.4.0</span>
+
+> **Warning:**
+>
+> Currently, Top SQL is an experimental feature. It is not recommended that you use it for production environments.
+
+- Scope: GLOBAL
+- Default value: `OFF`
+- This variable is used to control whether to enable the [Top SQL](/dashboard/top-sql.md) feature.
+


This was previously at the bottom of the page (non alphabetical order). Chronological order doesn't make sense to users, so the order is fixed.

the default value of tidb_enable_top_sql is "ON" in v6.0.0

morgo · 2022-03-02T23:44:28Z

system-variables.md

- Default value: `0`
+- Default value: ""


According the the source, the default is "". But it might be a bug: pingcap/tidb#32763

In either case, it's correct right now - but it should be changed in future to be numeric. This will also help improve the docs as the type is shown.

morgo · 2022-03-02T23:45:10Z

system-variables.md

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

-> **WARNING:**
+> **Warning:**


These two variables were in the wrong alphabetical order. Warning is also in upper case (inconsistent).

morgo · 2022-03-02T23:46:25Z

system-variables.md

- Scope: SESSION | GLOBAL
+- Scope: GLOBAL
 - Default value: `24`
 - Range: `[0, 255]`
 - This variable is used to set the history capacity of [statement summary tables](/statement-summary-tables.md).

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

- Scope: SESSION | GLOBAL
+- Scope: GLOBAL
 - Default value: `OFF`
 - This variable is used to control whether to include the SQL information of TiDB in [statement summary tables](/statement-summary-tables.md).

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

- Scope: SESSION | GLOBAL
+- Scope: GLOBAL
 - Default value: `4096`
 - Range: `[0, 2147483647]`
 - This variable is used to control the length of the SQL string in [statement summary tables](/statement-summary-tables.md).

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

- Scope: SESSION | GLOBAL
+- Scope: GLOBAL
 - Default value: `3000`
 - Range: `[1, 32767]`
 - This variable is used to set the maximum number of statements that [statement summary tables](/statement-summary-tables.md) store in memory.

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

- Scope: SESSION | GLOBAL


This behavior change is intentional and only affects master. See: https://github.com/pingcap/tidb/blob/master/docs/design/2021-12-08-instance-scope.md

morgo · 2022-03-02T23:46:44Z

system-variables.md

-### `tidb_enable_top_sql` <span class="version-mark">New in v5.4.0</span>
-
- Scope: GLOBAL
- Default value: `OFF`
- This variable is used to control whether to enable the [Top SQL](/dashboard/top-sql.md) feature.
-
-> **Warning:**
->
-> Currently, Top SQL is an experimental feature. It is not recommended that you use it for production environments.
-


This was moved higher up in the document (correct alphabetical order).

morgo · 2022-03-02T23:47:35Z

system-variables.md

- Default value: `lower, md5, reverse, upper, vitess_hash`
+- Default value: `lower, md5, reverse, tidb_shard, upper, vitess_hash`


This is according to the generated source. The default has changed.

morgo · 2022-03-04T16:09:42Z

I think there will be other updates. It looks like a lot of new sysvars were added which are not documented yet:

 124                 variable.TiDBSuperReadOnly,
 125                 variable.TiDBTableCacheLease,
 126                 variable.TiDBTopSQLMaxMetaCount,
 127                 variable.TiDBTopSQLMaxTimeSeriesCount,
 128                 variable.TiDBTxnAssertionLevel,
 129                 variable.TiDBPlacementMode,
 130                 variable.TiDBReadConsistency,
 131                 variable.TiDBEnableMutationChecker,
 132                 variable.TiDBLastDDLInfo,
 133                 variable.TiDBMemQuotaBindCache,
 134                 variable.SysdateIsNow

So it would be good to merge this first if that's possible :-)

mjonss

LGTM and thank you for the helpful comments!

bb7133

LGTM

bb7133 · 2022-03-15T16:25:14Z

/merge

ti-chi-bot · 2022-03-15T16:25:16Z

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morgo · 2022-03-22T02:17:23Z

/merge

ti-chi-bot · 2022-03-22T02:17:26Z

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seiya-annie · 2022-03-22T02:35:17Z

system-variables.md

- This variable controls how TiDB behaves when the waiting time of SQL optimization reaches the timeout to synchronously load complete column statistics. The default value `OFF` means that SQL execution fails after the timeout. If you set this variable to `ON`, the SQL optimization gets back to using pseudo statistics after the timeout.
+- Scope: SESSION | GLOBAL
+- Default value: `0`
+- Range: `[0, 2147483647]`


Does the value range changed? from [0, 4294967295]` changed to [0, 2147483647]?

It's not specifically changed, it was always wrong. See: pingcap/tidb#30026 where it was introduced.

math.MaxInt32 == 32 bit signed integer (max = 2147483647).

morgo · 2022-03-22T02:47:13Z

/merge

ti-chi-bot · 2022-03-22T02:47:15Z

@morgo: /merge in this pull request requires 2 approval(s).

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/merge

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TomShawn · 2022-03-22T02:49:03Z

/remove-status LGT1
/status LGT3

TomShawn · 2022-03-22T02:49:14Z

/merge

ti-chi-bot · 2022-03-22T02:49:16Z

This pull request has been accepted and is ready to merge.

Commit hash: 9f240cb

system-variables: update from generated source

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ti-chi-bot requested a review from TomShawn March 2, 2022 23:39

ti-chi-bot added missing-translation-status This PR does not have translation status info. size/L Denotes a PR that changes 100-499 lines, ignoring generated files. labels Mar 2, 2022

morgo commented Mar 2, 2022

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Update system-variables.md

9f240cb

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The order of system variables is messy. pingcap/tidb#33086

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ti-chi-bot merged commit 8c84c9c into pingcap:master Mar 22, 2022

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system-variables: update from generated source pingcap/docs-cn#8720

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update statement summary variables scope #8268

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docs for instance scoped system variables #7897

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update statement summary variables scope (#8268) #8613

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system-variables: update from generated source #7737

system-variables: update from generated source #7737

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		- Default value: `lower, md5, reverse, upper, vitess_hash`
		- Default value: `lower, md5, reverse, tidb_shard, upper, vitess_hash`

system-variables: update from generated source #7737

system-variables: update from generated source #7737

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morgo commented Mar 2, 2022 • edited by TomShawn Loading

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