Merge branch 'master' into missing_sysvars_2

TOC.md

@@ -557,17 +557,20 @@
   + [All Releases](/releases/release-notes.md)
   + v5.2
     + [5.2.1](/releases/release-5.2.1.md)
-    + [5.2.0](/releases/release-5.2.0.md)  
+    + [5.2.0](/releases/release-5.2.0.md)
   + v5.1
+    + [5.1.2](/releases/release-5.1.2.md)
     + [5.1.1](/releases/release-5.1.1.md)
     + [5.1.0](/releases/release-5.1.0.md)
   + v5.0
+    + [5.0.4](/releases/release-5.0.4.md)
     + [5.0.3](/releases/release-5.0.3.md)
     + [5.0.2](/releases/release-5.0.2.md)
     + [5.0.1](/releases/release-5.0.1.md)
     + [5.0 GA](/releases/release-5.0.0.md)
     + [5.0.0-rc](/releases/release-5.0.0-rc.md)
   + v4.0
+    + [4.0.15](/releases/release-4.0.15.md)
     + [4.0.14](/releases/release-4.0.14.md)
     + [4.0.13](/releases/release-4.0.13.md)
     + [4.0.12](/releases/release-4.0.12.md)

adopters.md

@@ -14,7 +14,6 @@ This is a list of TiDB adopters in various industries.
 |[VNG](https://en.wikipedia.org/wiki/VNG_Corporation)|Mobile Payment|English [#1](https://pingcap.com/case-studies/tidb-at-zalopay-infrastructure-lesson-learned/), [#2](https://pingcap.com/case-studies/zalopay-using-a-scale-out-mysql-alternative-to-serve-millions-of-users)|
 |[Ping++](https://www.crunchbase.com/organization/ping-5)|Mobile Payment||
 |[LianLian Tech](https://www.crunchbase.com/organization/lianlian-pay)|Mobile Payment||
-|[Pinterest](https://en.wikipedia.org/wiki/Pinterest)|Media and Entertainment|[English](https://pingcap.com/case-studies/how-pinterest-reduced-costs-and-improved-data-consistency-with-newsql-database)|
 |[U-Next](https://www.crunchbase.com/organization/u-next)|Media and Entertainment|[English](https://pingcap.com/case-studies/running-a-scale-out-database-on-arm-as-mysql-alternative/)|
 |[Dailymotion](https://en.wikipedia.org/wiki/Dailymotion)|Media and Entertainment||
 |[iQiyi](https://en.wikipedia.org/wiki/IQiyi)|Media and Entertainment|[English](https://pingcap.com/case-studies/tidb-in-iqiyi/)|
@@ -66,6 +65,7 @@ This is a list of TiDB adopters in various industries.
 |[SEA group](https://sea-group.org/?lang=en)|Gaming||
 |[Zhaopin.com](https://www.crunchbase.com/organization/zhaopin)|Recruiting||
 |[BIGO](https://www.crunchbase.com/organization/bigo-technology)|Live Streaming|[English](https://pingcap.com/case-studies/why-we-chose-an-htap-database-over-mysql-for-horizontal-scaling-and-complex-queries/); [Chinese](https://pingcap.com/cases-cn/user-case-bigo/)|
+|[Huya Live](https://en.wikipedia.org/wiki/Huya_Live)|Live Streaming|[English](https://pingcap.com/case-studies/how-we-scale-out-databases-and-get-big-data-queries-6x-faster-with-a-mysql-alternative); [Chinese](https://pingcap.com/zh/case/user-case-huya)|
 |[Panda.tv](https://www.crunchbase.com/organization/panda-tv)|Live Streaming||
 |[Phoenix New Media](https://www.crunchbase.com/organization/phoenix-new-media)|Media||
 |[Tencent OMG](https://en.wikipedia.org/wiki/Tencent)|Media||

enable-tls-between-clients-and-servers.md

@@ -38,7 +38,7 @@ Similar to MySQL, the encrypted connections in TiDB consist of single connection
 
 ## Configure TiDB to use encrypted connections
 
-See the following desrciptions about the related parameters to enable encrypted connections:
+See the following descriptions about the related parameters to enable encrypted connections:
 
 - [`ssl-cert`](/tidb-configuration-file.md#ssl-cert): specifies the file path of the SSL certificate
 - [`ssl-key`](/tidb-configuration-file.md#ssl-key): specifies the private key that matches the certificate

faq/sql-faq.md

@@ -187,11 +187,12 @@ SELECT column_name FROM table_name USE INDEX（index_name）WHERE where_conditio
 
 TiDB handles the SQL statement using the `schema` of the time and supports online asynchronous DDL change. A DML statement and a DDL statement might be executed at the same time and you must ensure that each statement is executed using the same `schema`. Therefore, when the DML operation meets the ongoing DDL operation, the `Information schema is changed` error might be reported. Some improvements have been made to prevent too many error reportings during the DML operation.
 
-Now, there are still a few reasons for this error reporting (the latter two are unrelated to tables):
+Now, there are still a few reasons for this error reporting (only the first one is related to tables):
 
 + Some tables involved in the DML operation are the same tables involved in the ongoing DDL operation.
 + The DML operation goes on for a long time. During this period, many DDL statements have been executed, which causes more than 1024 `schema` version changes. You can modify this default value by modifying the `tidb_max_delta_schema_count` variable.
 + The TiDB server that accepts the DML request is not able to load `schema information` for a long time (possibly caused by the connection failure between TiDB and PD or TiKV). During this period, many DDL statements have been executed, which causes more than 100 `schema` version changes.
++ After TiDB restarts and before the first DDL operation is executed, the DML operation is executed and then encounters the first DDL operation (which means before the first DDL operation is executed, the transaction corresponding to the DML is started. And after the first `schema` version of the DDL is changed, the transaction corresponding to the DML is committed), this DML operation reports this error.
 
 > **Note:**
 >

functions-and-operators/aggregate-group-by-functions.md

@@ -154,3 +154,7 @@ group by id, val;
 The following aggregate functions are currently unsupported in TiDB. You can track our progress in [TiDB #7623](https://github.com/pingcap/tidb/issues/7623):
 
 - `JSON_ARRAYAGG`
+
+## Related system variables
+
+The `group_concat_max_len` variable sets the maximum number of items for the `GROUP_CONCAT()` function.

functions-and-operators/date-and-time-functions.md

@@ -74,3 +74,7 @@ TiDB supports all of the [date and time functions](https://dev.mysql.com/doc/ref
 | [`YEARWEEK()`](https://dev.mysql.com/doc/refman/5.7/en/date-and-time-functions.html#function_yearweek) | Return the year and week                 |
 
 For details, see [Date and Time Functions](https://dev.mysql.com/doc/refman/5.7/en/date-and-time-functions.html).
+
+## Related system variables
+
+The `default_week_format` variable affects the `WEEK()` function.

functions-and-operators/encryption-and-compression-functions.md

@@ -32,6 +32,10 @@ TiDB supports most of the [encryption and compression functions](https://dev.mys
 | [`ASYMMETRIC_SIGN()`](https://dev.mysql.com/doc/refman/5.7/en/enterprise-encryption-functions.html#function_asymmetric-sign)                          | Generate signature from digest                    |
 | [`ASYMMETRIC_VERIFY()`](https://dev.mysql.com/doc/refman/5.7/en/enterprise-encryption-functions.html#function_asymmetric-verify)                      | Verify that signature matches digest              |
 
+## Related system variables
+
+The `block_encryption_mode` variable sets the encryption mode that is used for `AES_ENCRYPT()` and `AES_DECRYPT()`.
+
 ## Unsupported functions
 
 * `DES_DECRYPT()`, `DES_ENCRYPT()`, `OLD_PASSWORD()`, `ENCRYPT()`: these functions were deprecated in MySQL 5.7 and removed in 8.0.

mysql-compatibility.md

@@ -6,7 +6,7 @@ aliases: ['/docs/dev/mysql-compatibility/','/docs/dev/reference/mysql-compatibil
 
 # MySQL Compatibility
 
-TiDB is fully compatible with the MySQL 5.7 protocol and the common features and syntax of MySQL 5.7. The ecosystem tools for MySQL 5.7 (PHPMyAdmin, Navicat, MySQL Workbench, mysqldump, and Mydumper/myloader) and the MySQL client can be used for TiDB.
+TiDB is highly compatible with the MySQL 5.7 protocol and the common features and syntax of MySQL 5.7. The ecosystem tools for MySQL 5.7 (PHPMyAdmin, Navicat, MySQL Workbench, mysqldump, and Mydumper/myloader) and the MySQL client can be used for TiDB.
 
 However, some features of MySQL are not supported. This could be because there is now a better way to solve the problem (such as XML functions superseded by JSON), or a lack of current demand versus effort required (such as stored procedures and functions). Some features might also be difficult to implement as a distributed system.
 

pd-configuration-file.md

@@ -268,11 +268,15 @@ Configuration items related to scheduling
 + Determines whether to enable the merging of cross-table Regions
 + Default value: `true`
 
-### `region-score-formula-version`
+### `region-score-formula-version` <span class="version-mark">New in v5.0</span> 
 
 + Controls the version of the Region score formula
 + Default value: `v2`
-+ Optional values: `v1` and `v2`
++ Optional values: `v1` and `v2`. Compared to v1, the changes in v2 are smoother, and the scheduling jitter caused by space reclaim is improved.
+
+> **Note:**
+>
+> If you have upgraded your cluster from a TiDB 4.0 version to the current version, the new formula version is automatically disabled by default to ensure consistent PD behavior before and after the upgrading. If you want to change the formula version, you need to manually switch through the `pd-ctl` setting. For details, refer to [PD Control](/pd-control.md#config-show--set-option-value--placement-rules).
 
 ### `enable-joint-consensus` <span class="version-mark">New in v5.0</span>
 
@@ -317,6 +321,10 @@ Configuration items related to replicas
 + Default value: 3
 + PD rounds the lowest digits of the flow number, which reduces the update of statistics caused by the changes of the Region flow information. This configuration item is used to specify the number of lowest digits to round for the Region flow information. For example, the flow `100512` will be rounded to `101000` because the default value is `3`. This configuration replaces `trace-region-flow`.
 
+> **Note:**
+>
+> If you have upgraded your cluster from a TiDB 4.0 version to the current version, the behavior of `flow-round-by-digit` after the upgrading and the behavior of `trace-region-flow` before the upgrading are consistent by default. This means that if the value of  `trace-region-flow` is false before the upgrading, the value of `flow-round-by-digit` after the upgrading is 127; if the value of `trace-region-flow` is `true` before the upgrading, the value of `flow-round-by-digit` after the upgrading is `3`.
+
 ## `label-property`
 
 Configuration items related to labels