Updated on 2025-08-29 GMT+08:00

Constraints

Usage Constraints

  • Data is synchronized from OLTP to OLAP through binlogs. Large transactions and substantial data updates on the OLTP side can lead to significant latency in OLAP data.
  • When you query data in an HTAP instance, character string comparison and the names of databases, tables, views, users, and roles are case sensitive, but the names of columns and partitions are case insensitive.
  • A Duplicate Key table is used when tables without primary keys in a TaurusDB instance are synchronized to an HTAP instance.
  • A primary key value can be a maximum of 128 bytes long.
  • The names of the databases and tables to be synchronized cannot contain Chinese characters.
  • To improve performance, you can use the following methods to optimize queries:
    • Simplify SQL statements by reducing invalid calculations, deleting unused fields, and avoiding SELECT.
    • Instead of querying all columns, delete those that are unnecessary.
  • Tables to be synchronized use the OLAP engine and primary key model by default.
  • After connecting to a standard HTAP instance, run the following command to view the databases synchronized from a TaurusDB instance to the standard HTAP instance and the synchronization status.
    This command queries binlog details in the TaurusDB instance and occupies the instance's hourly query quota. So, do not run this command too frequently. You are advised to run this command less than once per minute.
    show sync job;

DDL Synchronization Constraints

Some DDL statements executed on TaurusDB instances cannot be synchronized to HTAP instances. Attempting to synchronize these statements may cause synchronization failures or data inconsistencies.

The DDL statements that can be synchronized and cannot be synchronized are as follows:

View Synchronization Constraints

  • Views are not synchronized by default. If sync_view is set to true, data and views are synchronized. If sync_view is set to only_sync_view, only views are synchronized. only_sync_view is only supported for non-instance-level synchronization.
  • You can only create a view synchronization task after creating a data synchronization task.
  • View synchronization can be enabled for only one synchronization task of a given database.
  • When you select a synchronization view, the source database name must be the same as the destination database name.
  • Some view-related DDL statements cannot be synchronized, for example, the rename table statement used to rename a view.
  • A cross-database view may fail to be synchronized if dependent databases are not synchronized.
  • If a function or syntax that is not supported by HTAP instances is used in a view, the view cannot be synchronized.
  • If a view fails to be synchronized, you can manually create it on an HTAP instance after the fault is rectified.
  • When view synchronization fails, alarms and error information are reported. You can connect to an HTAP instance and run show sync job to view SyncErrViews (views that failed to be synchronized) and SyncErrMsg (detailed error information). To clear alarms and error information, you can run alter sync synchronization_task_name setting "SyncErrViewMsg" = "", "SyncErrViews"="";
  • View synchronization failures do not affect table data synchronization.
  • The kernel version of your TaurusDB instance must be 2.0.57.240900 or later. For details about how to check the kernel version, see How Can I Check the Version of a TaurusDB Instance?