TDengine Frequently Asked Questions (FAQ)

1. What should I pay attention to when upgrading the version before TDengine 2.0 to the version 2.0 and above? ☆☆☆

Version 2.0 has been completely refactored on the basis of the previous version, and the configuration files and data files are incompatible. Be sure to do the following before upgrading:

delete the configuration file, executesudo rm -rf /etc/taos/taos.cfg

delete log file, executesudo rm -rf /var/log/taos/

Make sure that the data is no longer needed, delete the data file, and execute to sudo rm -rf /var/lib/taos/install the latest stable version of TDengine

If the data needs to be migrated or the data files are damaged, please contact the official technical support team of Taos Data ([email protected]) for assistance.

2. JDBCDriver cannot find the dynamic link library under Windows platform, what should I do?

Please see the technical blog written for this issue

3. When creating a data table, it prompts that more dnodes are needed

Please see the technical blog written for this issue

4. How to generate core files when TDengine crashes?

Please see the technical blog written for this issue

5. I encounter the error "Unable to establish connection", what should I do?

The client is experiencing a link failure, please follow the steps below to check:

1. Check the network environment

Cloud server : Check whether the security group of the cloud server has open access to TCP/UDP ports 6030-6042

Local virtual machine : check whether the network can be pinged, try to avoid using localhost as the hostname

Company server : If it is a NAT network environment, be sure to check whether the server can return messages to the client

2. Ensure that the client and server version numbers are exactly the same, and the open source community edition and enterprise edition cannot be mixed

3. On the server, execute systemctl status taosd to check the running status of taosd. If not running, start taosd

4. Confirm that the correct server FQDN (Fully Qualified Domain Name (Fully Qualified Domain Name) is specified when the client connects (can be obtained by executing the Linux command hostname -f on the server)

5. Ping the server FQDN, if there is no response, please check your network, DNS settings, or the system hosts file of the computer where the client is located

6. Check firewall settings to make sure TCP/UDP ports 6030-6042 are open

7. For JDBC (ODBC, Python, Go, etc. interfaces are similar) connections on Linux, make sure libtaos.so is in the directory /usr/local/lib/taos, and /usr/local/lib/taos is in the system library function search path LD_LIBRARY_PATH

8. For JDBC, ODBC, Python, Go and other connections on Windows, make sure driver/c/taos.dll is in your system search directory (it is recommended to put taos.dll in the directory C:\Windows\System32)

9. If the connection failure still cannot be eliminated, please use the command line tool nc to judge whether the TCP and UDP connections of the specified ports are smooth. Check whether the UDP port connection is working: nc -vuz {hostIP} {port} Check whether the TCP port connection on the server side is not Works: nc -l {port} Check if the client side TCP port link is working: nc {hostIP} {port}

10. You can also use the network connection detection function embedded in the taos program to verify whether the specified port connection between the server and the client is smooth (including TCP and UDP): TDengine Embedded Network Detection Tool User Guide

6. I encounter the error "Unexpected generic error in RPC" or "TDengine Error: Unable to resolve FQDN", what should I do?

This error occurs because the client or data node cannot resolve the FQDN (Fully Qualified Domain Name). For TAOS Shell or client applications, please check the following:

1. Please check if the FQDN of the connected server is correct
2. If the network is configured with a DNS server, please check if it is working properly
3. If the network is not configured with a DNS server, please check the hosts file of the machine where the client is located to see if the FQDN is configured and has a correct IP address.
4. If the network configuration is OK, from the machine where the client is located, you need to be able to ping the FQDN of the connection, otherwise the client cannot connect to the server

7. Why am I getting an "Invalid SQL" error even though the syntax is correct

If you confirm that the syntax is correct, before version 2.0, please check whether the SQL statement length exceeds 64K. If it exceeds, this error will also be returned.

8. Does it support validation queries?

TDengine does not yet have a dedicated set of validation queries. However, it is recommended that you use the system monitoring database "log" to do it.

9. Can I delete or update a record?

can not. Because TDengine is designed for data collected by networked devices, modification is not allowed. However, TDengine provides a data retention policy. As long as the data record exceeds the retention period, it will be automatically deleted.

10. How can I create a table with more than 1024 columns?

For versions 2.0 and above, 1024 columns are supported by default; for versions prior to 2.0, TDengine allows a maximum of 250 columns to be created. But if it does exceed the limit, it is recommended to logically decompose this wide table into several small tables according to the characteristics of the data.

11. What is the most efficient way to write data?

Bulk insert. Each write statement can insert multiple records from one table at the same time, or insert multiple records from multiple tables at the same time.

12. How to solve the problem that the Chinese characters in the nchar data inserted under the windows system are parsed into garbled characters?

If there is Chinese in the data of the nchar class inserted under windows, please confirm that the system region is set to China (can be set in the Control Panel), then the taos client in cmd should be able to work normally; if it is in the IDE To develop Java applications in the IDE, such as Eclipse and Intellij, please confirm that the file encoding in the IDE is GBK (this is the default encoding type of Java), and then initialize the configuration of the client when the Connection is generated. The specific statements are as follows:

Class.forName("com.taosdata.jdbc.TSDBDriver");
Properties properties = new Properties();
properties.setProperty(TSDBDriver.LOCALE_KEY, "UTF-8");
Connection = DriverManager.getConnection(url, properties);

13.How to compile TDengine GO windows driver?

Please see the technical blog written for this issue

14. JDBC报错： the excuted SQL is not a DML or a DDL？

Please update to the latest JDBC driver

<dependency>
  <groupId>com.taosdata.jdbc</groupId>
  <artifactId>taos-jdbcdriver</artifactId>
  <version>2.0.4</version>
</dependency>

15. How do I report a problem?

If the information in the FAQ cannot help you and you need technical support and assistance from the TDengine technical team , please package the contents in the following two directories:

/var/log/taos
/etc/taos

Attach the necessary description of the problem, as well as the execution of the problem, the characterization of the problem and the approximate time, and submit an Issue on GitHub .

In order to ensure that there is enough debug information, if the problem can be repeated, please modify the /etc/taos/taos.cfg file, add a line "debugFlag 135" (without the quotation marks itself) at the end, then restart taosd, repeat the problem, and then submit . However, when the system is running normally, be sure to set the debugFlag to 131, otherwise a large amount of log information will be generated and the system efficiency will be reduced.

{{o.name}}

{{m.name}}