TDengine

Supported since 5.4.0.

Through the TDengine (opens new window) connector, Ontop is able to construct VKGs on TDengine databases.

Limitations & Exceptions

• As a time-series database, TDengine expects that all tables have a timestamp as their first column which is also used as a primary key.
• TDengine has limited support regarding date/time types. In particular, it does not support the TIMESTAMP WITH TIME ZONE, DATE, and TIME types and instead only uses TIMESTAMP
• Some data types, mainly DECIMAL and the UNSIGNED variants of integer types, are only supported through the WebSocket connection and are not currently supported by Ontop.

Database Connection

There are three ways to connect Ontop to a TDengine database using the JDBC driver:

• Native connection: depends on the client driver (libtaos.so on Linux, taos.dll on Windows, and libtaos.dylib on macOS). Below is an example of a .properties file that can be used to connect Ontop to TDengine using the native driver:

  jdbc.url = jdbc:TAOS://hostname:6030/dbname
  jdbc.driver = com.taosdata.jdbc.TSDBDriver
  

• WebSocket connection: does not require any additional client driver. Below is an example of a .properties file that can be used to connect Ontop to TDengine using the WebSocket connection:

  jdbc.url = jdbc:TAOS-WS://hostname:6041/dbname
  jdbc.driver = com.taosdata.jdbc.ws.WebSocketDriver
  

• Restful connection: it is now recommended to use the WebSocket connection instead, as it achieves better performance. Nevertheless, it is still supported so below is an example of a .properties file that can be used to connect Ontop to TDengine using the Restful connection:

  jdbc.url = jdbc:TAOS-RS://hostname:6041/dbname
  jdbc.driver = com.taosdata.jdbc.rs.RestfulDriver
  

NOTE

While all three connection methods are supported, the WebSocket connection is the recommended one, as it provides the best performance without any client compatibility issues.

Nested Type Support

TDengine has some limited support for JSON data through the JSON data type. The main limitation is that the JSON data type can only be used in tag columns of supertables, and it cannot have a nested structure (i.e., arrays or objects inside the JSON are not allowed).

Ontop does not support nested data types or flatten lenses for TDengine.