FQDN（Fully Qualified Domain Name，完全限定域名）是 Internet 上特定计算机或主机的完整域名。FQDN 由两部分组成:主机名和域名。例如，假设邮件服务器的 FQDN 可能是 mail.tdengine.com。主机名是 mail，主机位于域名 tdengine.com 中。DNS（Domain Name System），负责将 FQDN 翻译成 IP，是互联网应用的寻址方式。对于没有 DNS 的系统，可以通过配置 hosts 文件来解决。
An instance is a running cluster of nodes of TDengine with one or more databases. An instance cannot span across multiple regions or multiple clouds. TDengine cloud provides a unique URL for each instance and uses tokens to authenticate the access. The token is generated by TDengine cloud for each user and for each instance. The token has an expiration date and can be reset by the user for each instance at any time for security purpose.
TDengine 集群的每个节点是由 Endpoint 来唯一标识的，Endpoint 是由 FQDN 外加 Port 组成，比如 h1.tdengine.com:6030。这样当 IP 发生变化的时候，我们依然可以使用 FQDN 来动态找到节点，不需要更改集群的任何配置。而且采用 FQDN，便于内网和外网对同一个集群的统一访问。
1.backing up all databases: specify `-A` or `-all-databases` parameter.
1. 备份所有数据库：指定 `-A` 或 `--all-databases` 参数；
2.backup multiple specified databases: use `-D db1,db2,...` parameters;
2. 备份多个指定数据库：使用 `-D db1,db2,...` 参数；
3.back up some super or normal tables in the specified database: use `-dbname stbname1 stbname2 tbname1 tbname2 ...` parameters. Note that the first parameter of this input sequence is the database name, and only one database is supported. The second and subsequent parameters are the names of super or normal tables in that database, separated by spaces.
4.back up the system log database: TDengine clusters usually contain a system database named `log`. The data in this database is the data that TDengine runs itself, and the taosdump will not back up the log database by default. If users need to back up the log database, users can use the `-a` or `-allow-sys` command-line parameter.
5.Loose mode backup: taosdump version 1.4.1 onwards provides `-n` and `-L` parameters for backing up data without using escape characters and "loose" mode, which can reduce the number of backups if table names, column names, tag names do not use escape characters. This can also reduce the backup data time and backup data footprint. If you are unsure about using `-n` and `-L` conditions, please use the default parameters for "strict" mode backup. See the [official documentation](https://docs.tdengine.com/taos-sql/escape/) for a description of escaped characters.
- taosdump versions after 1.4.1 provide the `-I` argument for parsing Avro file schema and data. If users specify `-s` then only taosdump will parse schema.
-Backups after taosdump 1.4.2 use the batch count specified by the `-B` parameter. The default value is 16384. If, in some environments, low network speed or disk performance causes "Error actual dump ... batch ...", then try changing the `-B` parameter to a smaller value.
Restore the data file in the specified path: use the `-i` parameter plus the path to the data file. You should not use the same directory to backup different data sets, and you should not backup the same data set multiple times in the same path. Otherwise, the backup data will cause overwriting or multiple backups.
taosdump internally uses TDengine stmt binding API for writing recovery data with a default batch size of 16384 for better data recovery performance. If there are more columns in the backup data, it may cause a "WAL size exceeds limit" error. You can try to adjust the batch size to a smaller value by using the `-B` parameter.
