Add shard-row-id-bits.md doc and fix some links (#3239) (#3267)

Signed-off-by: ti-srebot <ti-srebot@pingcap.com>

TOC.md

@@ -204,6 +204,7 @@
       + Attributes
         + [AUTO_INCREMENT](/auto-increment.md)
         + [AUTO_RANDOM](/auto-random.md)
+        + [SHARD_ROW_ID_BITS](/shard-row-id-bits.md)
       + [Literal Values](/literal-values.md)
       + [Schema Object Names](/schema-object-names.md)
       + [Keywords and Reserved Words](/keywords.md)

best-practices/high-concurrency-best-practices.md

@@ -181,7 +181,7 @@ In this case, the table is simple. In other cases, you might also need to consid
 
 **Problem one:**
 
-If a table does not have a primary key, or the primary key is not the `Int` type and you do not want to generate a randomly distributed primary key ID, TiDB provides an implicit `_tidb_rowid` column as the row ID. Generally, when you do not use the `SHARD_ROW_ID_BITS` parameter, the values of the `_tidb_rowid` column are also monotonically increasing, which might causes hotspots too. Refer to [`SHARD_ROW_ID_BITS`](/sql-statements/sql-statement-create-table.md#shard_row_id_bits) for more details.
+If a table does not have a primary key, or the primary key is not the `Int` type and you do not want to generate a randomly distributed primary key ID, TiDB provides an implicit `_tidb_rowid` column as the row ID. Generally, when you do not use the `SHARD_ROW_ID_BITS` parameter, the values of the `_tidb_rowid` column are also monotonically increasing, which might causes hotspots too. Refer to [`SHARD_ROW_ID_BITS`](/shard-row-id-bits.md) for more details.
 
 To avoid the hotspot problem in this situation, you can use `SHARD_ROW_ID_BITS` and `PRE_SPLIT_REGIONS` when creating a table. For more details about `PRE_SPLIT_REGIONS`, refer to [Pre-split Regions](/sql-statements/sql-statement-split-region.md#pre_split_regions).
 

faq/tidb-faq.md

@@ -1089,7 +1089,7 @@ See [The TiDB Command Options](/command-line-flags-for-tidb-configuration.md).
 
 #### How to scatter the hotspots?
 
-In TiDB, data is divided into Regions for management. Generally, the TiDB hotspot means the Read/Write hotspot in a Region. In TiDB, for the table whose primary key (PK) is not an integer or which has no PK, you can properly break Regions by configuring `SHARD_ROW_ID_BITS` to scatter the Region hotspots. For details, see the introduction of `SHARD_ROW_ID_BITS` in [`CREATE TABLE`](/sql-statements/sql-statement-create-table.md#shard_row_id_bits).
+In TiDB, data is divided into Regions for management. Generally, the TiDB hotspot means the Read/Write hotspot in a Region. In TiDB, for the table whose primary key (PK) is not an integer or which has no PK, you can properly break Regions by configuring `SHARD_ROW_ID_BITS` to scatter the Region hotspots. For details, see the introduction of [`SHARD_ROW_ID_BITS`](/shard-row-id-bits.md).
 
 ### TiKV
 

shard-row-id-bits.md

@@ -0,0 +1,23 @@
+---
+title: SHARD_ROW_ID_BITS
+summary: Learn the SHARD_ROW_ID_BITS attribute.
+---
+
+# SHARD_ROW_ID_BITS
+
+This document introduces the `SHARD_ROW_ID_BITS` table attribute, which is used to set the number of bits of the shards after the implicit `_tidb_rowid` is sharded.
+
+## Concept
+
+For the tables with a non-integer primary key or no primary key, TiDB uses an implicit auto-increment row ID. When a large number of `INSERT` operations are performed, the data is written into a single Region, causing a write hot spot.
+
+To mitigate the hot spot issue, you can configure `SHARD_ROW_ID_BITS`. The row IDs are scattered and the data are written into multiple different Regions. But setting an overlarge value might lead to an excessively large number of RPC requests, which increases the CPU and network overheads.
+
+- `SHARD_ROW_ID_BITS = 4` indicates 16 shards
+- `SHARD_ROW_ID_BITS = 6` indicates 64 shards
+- `SHARD_ROW_ID_BITS = 0` indicates the default 1 shard
+
+## Examples
+
+- `CREATE TABLE`: `CREATE TABLE t (c int) SHARD_ROW_ID_BITS = 4;`
+- `ALTER TABLE`: `ALTER TABLE t SHARD_ROW_ID_BITS = 4;`

sql-statements/sql-statement-alter-table.md

@@ -59,21 +59,6 @@ mysql> EXPLAIN SELECT * FROM t1 WHERE c1 = 3;
 2 rows in set (0.00 sec)
 ```
 
-## SHARD_ROW_ID_BITS
-
-For tables with a non-integer `PRIMARY KEY` or without a `PRIMARY KEY`, TiDB uses an implicit auto-increment ROW ID. Because regions are automatically sharded using a range-based scheme on the `PRIMARY KEY`, hotspots can occur when there are a large number of `INSERT` operations.
-
-To mitigate the hot spot issue, you can configure `SHARD_ROW_ID_BITS`. The ROW ID is scattered and the data is written into multiple different Regions. But setting an overlarge value might lead to an excessively large number of RPC requests, which increases the CPU and network overhead.
-
-- `SHARD_ROW_ID_BITS = 4` indicates 16 shards
-- `SHARD_ROW_ID_BITS = 6` indicates 64 shards
-- `SHARD_ROW_ID_BITS = 0` indicates the default 1 shard
-
-Usage:
-
-- `CREATE TABLE`: `CREATE TABLE t (c int) SHARD_ROW_ID_BITS = 4;`
-- `ALTER TABLE`: `ALTER TABLE t SHARD_ROW_ID_BITS = 4;`
-
 ## MySQL compatibility
 
 * All of the data types except spatial types are supported. For other unsupported cases, refer to: [compatibility of DDL statements with MySQL](/mysql-compatibility.md#ddl).

sql-statements/sql-statement-create-table.md

@@ -224,7 +224,7 @@ table_option:
   | STATS_PERSISTENT [=] {DEFAULT|0|1}
 ```
 
-The `table_option` currently only supports `AUTO_INCREMENT`, `SHARD_ROW_ID_BITS`, `PRE_SPLIT_REGIONS`, `CHARACTER SET`, `COLLATE`, and `COMMENT`, while the others are only supported in syntax. The clauses are separated by a comma `,`. See the following table for details:
+The `table_option` currently only supports `AUTO_INCREMENT`, [`SHARD_ROW_ID_BITS`](/shard-row-id-bits.md), `PRE_SPLIT_REGIONS`, `CHARACTER SET`, `COLLATE`, and `COMMENT`, while the others are only supported in syntax. The clauses are separated by a comma `,`. See the following table for details:
 
 | Parameters | Description | Example |
 | ---------- | ---------- | ------- |
@@ -269,21 +269,6 @@ mysql> SELECT * FROM t1;
 1 row in set (0.00 sec)
 ```
 
-## SHARD_ROW_ID_BITS
-
-For tables with a non-integer `PRIMARY KEY` or without a `PRIMARY KEY`, TiDB uses an implicit auto-increment ROW ID. Because regions are automatically sharded using a range-based scheme on the `PRIMARY KEY`, hotspots can occur when there are a large number of `INSERT` operations.
-
-To mitigate the hot spot issue, you can configure `SHARD_ROW_ID_BITS`. The ROW ID is scattered and the data is written into multiple different Regions. But setting an overlarge value might lead to an excessively large number of RPC requests, which increases the CPU and network overhead.
-
-- `SHARD_ROW_ID_BITS = 4` indicates 16 shards
-- `SHARD_ROW_ID_BITS = 6` indicates 64 shards
-- `SHARD_ROW_ID_BITS = 0` indicates the default 1 shard
-
-Usage:
-
-- `CREATE TABLE`: `CREATE TABLE t (c int) SHARD_ROW_ID_BITS = 4;`
-- `ALTER TABLE`: `ALTER TABLE t SHARD_ROW_ID_BITS = 4;`
-
 ## MySQL compatibility
 
 * TiDB does not support temporary tables, but it ignores the `CREATE TEMPORARY TABLE` syntax.