Add TiDB limitations (#2899)

* Add TiDB limitations

* Update tidb-limitations.md

* address comments from lilian

* Update tidb-limitations.md

Co-authored-by: Keke Yi <40977455+yikeke@users.noreply.github.com>
Co-authored-by: Lilian Lee <lilin@pingcap.com>
Co-authored-by: ti-srebot <66930949+ti-srebot@users.noreply.github.com>

TOC.md

@@ -11,6 +11,7 @@
   + [Key Features](/key-features.md)
   + Compatibility
     + [MySQL Compatibility](/mysql-compatibility.md)
+  + [TiDB Limitations](/tidb-limitations.md)
 + Quick Start
   + [Try Out TiDB](/quick-start-with-tidb.md)
   + [Learn TiDB SQL](/basic-sql-operations.md)

tidb-limitations.md

@@ -0,0 +1,74 @@
+---
+title: TiDB Limitations
+summary: Learn the usage limitations of TiDB.
+category: introduction
+---
+
+# TiDB Limitations
+
+This document describes the common usage limitations of TiDB, including the maximum identifier length and the maximum number of supported databases, tables, indexes, partitioned tables, and sequences.
+
+## Limitations on identifier length
+
+| Identifier type | Maximum length (number of characters allowed) |
+|:---------|:--------------|
+| Database | 64 |
+| Table    | 64 |
+| Column   | 64 |
+| Index    | 64 |
+| View     | 64 |
+| Sequence | 64 |
+
+## Limitations on the total number of databases, tables, views, and connections
+
+| Identifier type  | Maximum number  |
+|:----------|:----------|
+| Databases | unlimited |
+| Tables    | unlimited |
+| Views     | unlimited |
+| Connections| unlimited|
+
+## Limitations on a single database
+
+| Type       | Upper limit   |
+|:----------|:----------|
+| Tables    | unlimited  |
+
+## Limitations on a single table
+
+| Type       | Upper limit   |
+|:----------|:----------|
+| Columns   | 512       |
+| Indexes    | 64        |
+| Rows      | unlimited |
+| Size      | unlimited |
+| Partitions | 1024      |
+
+## Limitation on a single row
+
+| Type       | Upper limit   |
+|:----------|:----------|
+| Size       | 6 MB       |
+
+## Limitation on a single column
+
+| Type       | Upper limit   |
+|:----------|:----------|
+| Size       | 6 MB       |
+
+## Limitations on string types
+
+| Type       | Upper limit   |
+|:----------|:----------|
+| CHAR       | 256 characters      |
+| BINARY     | 256 characters      |
+| VARBINARY  | 65535 characters    |
+| VARCHAR    | 16383 characters    |
+| TEXT       | 6 MB bytes      |
+| BLOB       | 6 MB bytes      |
+
+## Limitations on SQL statements
+
+| Type       | Upper limit   |
+|:----------|:----------|
+| The maximum number of SQL statements in a single transaction |  When the optimistic transaction is used and the transaction retry is enabled, the default upper limit is 5000, which can be modified using [`stmt-count-limit`](/tidb-configuration-file.md#stmt-count-limit). |