Usage Instructions
Last updated: 2025-09-11 14:38:00
Since TDSQL for MySQL (TDStore engine) is highly consistent with MySQL 8.0 in use, users can use it as a MySQL 8.0 instance. However, they should pay attention to the following points:
Syntax Not Supported by the TDStore Engine
The CREATE/ALTER/DROP syntax of the following objects is not supported.
event
resource group
instance
server
tablespace
spatial
SET GLOBAL log_output = TABLE: Outputting general_log and slow_log to the table is not supported, and only outputting to the file (namely slow query log file) is supported.
LOCK TABLE syntax is not currently supported (for data import and export tools that depend on LOCK TABLE syntax by default, it is recommended to use parameter settings to skip the execution of LOCK TABLE to avoid reporting errors, for example, mysqldump --lock-tables = false).
DDL operations on any system tables under the MySQL database are prohibited.
Foreign keys are not currently supported.
Modification of the table's storage engine is not allowed.
Virtual columns, GEOMETRY types, and descending indexes are not currently supported.
ALTER TABLE .. EXCHANGE PARTITION is not supported.
SAVEPOINT is not supported.
Spatial indexes are not supported.
Transportable tablespace is not supported.
Multi-valued indexes are not supported.
Fulltext indexes are not supported.
Group Replication is not supported.
Partial Update of LOB in InnoDB is not supported.
Adding columns containing DEFAULT EXPRESS using the INPLACE or ONLINE mode is not supported.
For example: ALTER TABLE t ADD COLUMN col INT DEFAULT 10 is supported, while ALTER TABLE t ADD COLUMN col INT DEFAULT (10) is not supported.
Experimental feature: The feature of the trigger in the current version is experimental. Therefore, it is not recommended for users to use it for formal production.
Note:
Each experimental feature has its independent switch and default value. To enable/disable it, users should connect to a TDStore instance and execute the following SQL statement (using tdsql_enable_trigger as an example):
SET PERSIST tdsql_enable_trigger=ON.Feature Name | Switch | Default Value |
Trigger | tdsql_enable_trigger | OFF |
Usage Differences Between TDStore Engine and MySQL 8.0
Currently, TDStore auto-increment fields are only guaranteed to be globally unique, and global monotonic increasing is not guaranteed.
Adding columns and adding/dropping indexes support online non-blocking read-write. Changing the column type and character set also supports online unlocked tables. Currently, the DDL operations that lock tables mainly include:
Add/drop the primary key.
rename column
Add/drop/change the auto-increment field.
When a column is added, the default value is in the form of an expression, for example, add column default (a+a).
The table does not have a primary key.
The table has an associated trigger.
When the system detects the DDL that does not support the online mode, it will give an error prompt. At this time, users can set set tdsql_use_online_copy_ddl = 0 to execute this type of DDL by locking the table.
set global xxx only sets the variable on a node. You need to use /*# broadcast */ set global xxx to broadcast it to all nodes for it to take effect globally.
show variables and show global status display the status information of the currently connected compute node. The information displayed may be different when different compute nodes are connected.
show processlist displays the processlist of the currently connected node. To display that of all nodes, you need to use /*# broadcast */show processlist.
Limit on the Number of Tables Created for TDStore Instances
The number of tables that can be created for each TDStore instance is limited as follows. This limit is related to the node specifications and the number of nodes constituting the instance. If this limit is exceeded, the corresponding error code (EC_MC_DATA_OBJ_LIMIT_EXCEEDED) will be returned.
Node Specification (CPU and Memory) | Maximum Number of Creatable Tables for Basic Edition Instances (Single-Node) | Maximum Number of Creatable Tables for Cluster Edition Instance (Three-Node) |
1 core and 2 GB | 10000 | 10000 |
2 cores and 4 GB | 10000 | 10000 |
4 cores and 8 GB | 10000 | 20000 |
8 cores and 16 GB | 10000 | 20000 |
16 cores and 32 GB | 20000 | 40000 |
32 cores and 64 GB | 40000 | 80000 |
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