CREATE SERVER

Function

CREATE SERVER creates an external server.

An external server stores information of HDFS clusters, OBS servers, DLI connections, or other homogeneous clusters.

Precautions

By default, only the system administrator can create a foreign server. Otherwise, creating a server requires USAGE permission on the foreign-data wrapper being used. The syntax is as follows:

1

GRANT USAGE ON FOREIGN DATA WRAPPER fdw_name TO username;

fdw_name is the name of FOREIGN DATA WRAPPER, and username is the user name of creating SERVER.

Syntax

1
2
3

CREATE SERVER server_name 
    FOREIGN DATA WRAPPER fdw_name
    OPTIONS ( { option_name ' value ' } [, ...] ) ;

Parameter Description

• server_name

  Name of the foreign server to be created. The server name must be unique in a database.

  Value range: The length must be less than or equal to 63.

• FOREIGN DATA WRAPPER fdw_name

  Specifies the name of the foreign data wrapper.

  Value range: fdw_name is the name of the data wrapper created by the system during database initialization. Currently, for the HDFS cluster, the value of fdw_name can be hdfs_fdw or dfs_fdw. For other homogeneous clusters, the value of fdw_name is gc_fdw. In data import and export scenarios, the GDS foreign table uses gsmpp_server and fdw_name is dist_fdw.

• OPTIONS ( { option_name ' value ' } [, ...] )

  Specifies the parameters for the server. The detailed parameter description is as follows:

  • address

    Specifies the IP address of the OBS service endpoint or HDFS cluster.

    OBS: Specifies the endpoint of the OBS service.

    HDFS: Specifies the IP address and port number of a NameNode (metadata node) in the HDFS cluster, or the IP address and port number of a CN in other homogeneous clusters.

    HDFS NameNodes are deployed in primary/secondary mode for HA. Add the addresses of the primary and secondary NameNodes to ADDRESS. When accessing HDFS, GaussDB(DWS) dynamically checks for the primary NameNode.

    If the HDFS is in federation mode, you can add all router addresses to the address value. When GaussDB(DWS) accesses the HDFS service, the system dynamically and randomly searches for the active router.

    

    • The address option must exist. In the cross-cluster interconnection scenario, only one address option can be set.
    • If the server type is DLI, the address is the OBS address stored on DLI.
    • If the HDFS is in federation mode, that is, fed 'rbf', address can be set to multiple groups of IP addresses and ports, corresponding to the address of the HDFS router.
  • hdfscfgpath

    This parameter is available only when type is HDFS.

    You can set the hdfscfgpath parameter to specify the HDFS configuration file path. GaussDB(DWS) accesses the HDFS cluster based on the connection configuration mode and security mode specified in the HDFS configuration file stored in that path. If the HDFS cluster is connected in non-secure mode, data transmission encryption is not supported.

    If the address option is not specified, the address specified by hdfscfgpath in the configuration file is used by default.

  • fed

    Indicates that dfs_fdw is connected to HDFS in federation mode.

    The value rbf indicates that HDFS uses the RBF mode.

    

    This feature is supported in 8.1.2 or later.

  • encrypt

    Specifies whether data is encrypted. This parameter is available only when type is OBS. The default value is off.

    Valid value:

    • on indicates that data is encrypted.
    • off indicates that data is not encrypted.
  • access_key

    Specifies the access key (AK) (obtained by users from the OBS console) used for the OBS access protocol. When you create a foreign table, its AK value is encrypted and saved to the metadata table of the database.

    

    • If FOREIGN DATA WRAPPER is set to dfs_fdw, this parameter can be set only when type is set to OBS.
    • For clusters of version 8.2.0 or later, this parameter can be specified when FOREIGN DATA WRAPPER is set to dist_fdw.
  • secret_access_key

    Indicates the secret access key (SK) (obtained by users from the OBS page) used for the OBS access protocol. When you create a foreign table, its SK value is encrypted and saved to the metadata table of the database.

    

    • If FOREIGN DATA WRAPPER is set to dfs_fdw, this parameter can be set only when type is set to OBS.
    • For clusters of 8.2.0 or later, this parameter can be specified when FOREIGN DATA WRAPPER is set to dist_fdw.
  • security_token

    Corresponds to the SecurityToken value of the temporary security credential in IAM. A temporary AK, a temporary SK, and a temporary security token form a temporary security credential. This parameter is supported by version 8.2.0 or later clusters.

    

    • If FOREIGN DATA WRAPPER is set to dfs_fdw, this parameter can be set only when type is set to OBS.
    • For clusters of 8.2.0 or later, this parameter can be specified when FOREIGN DATA WRAPPER is set to dist_fdw.
    • When this parameter is used, access_key and secret_access_key correspond to the temporary AK and SK, respectively.
  • type

    Specifies the dfs_fdw connection type.

    Valid value:

    • OBS indicates that OBS is connected.
    • HDFS indicates that HDFS is connected.
    • DLI indicates that DLI is connected.
  • dli_address

    Specifies the endpoint of the DLI service. This parameter is available only when type is DLI.

  • dli_access_key

    Specifies the access key (AK) (obtained by users from the DLI console) used for the DLI access protocol. When you create a foreign table, its AK value is encrypted and saved to the metadata table of the database. This parameter is available only when type is DLI.

  • dli_secret_access_key

    Specifies the secret access key (SK) (obtained by users from the DLI console) used for the DLI access protocol. When you create a foreign table, its SK value is encrypted and saved to the metadata table of the database. This parameter is available only when type is DLI.

  • dbname

    Specifies the database name of a remote cluster to be connected. This parameter is used for collaborative analysis and cross-cluster interconnection.

  • username

    Specifies the username of a remote cluster to be connected. This parameter is used for collaborative analysis and cross-cluster interconnection.

  • password

    Specifies the password of a remote cluster to be connected. This parameter is used for collaborative analysis and cross-cluster interconnection.

    

    When an on-premises cluster is migrated to the cloud, the password in the server configuration exported from the on-premises cluster is in ciphertext. The encryption and decryption keys of the on-premises cluster are different from those of the cloud cluster. Therefore, if CREATE SERVER is executed on the cloud cluster, the execution fails and a decryption failure error is reported. In this case, you need to manually change the password in CREATE SERVER to a plaintext password.

  • syncsrv

    This parameter is used only for cross-cluster interconnection and indicates the GDS service used during data synchronization. The method for setting this parameter is the same as that for setting the location attribute of the GDS foreign table.

Examples

Create the hdfs_server server, in which hdfs_fdw is the foreign-data wrapper:

1
2
3
4
5

CREATE SERVER hdfs_server FOREIGN DATA WRAPPER HDFS_FDW OPTIONS 
   (address '10.10.0.100:25000,10.10.0.101:25000',
    hdfscfgpath '/opt/hadoop_client/HDFS/hadoop/etc/hadoop', 
    type 'HDFS'
) ;

Create the obs_server server, in which dfs_fdw is the foreign-data wrapper:

1
2
3
4
5
6

CREATE SERVER obs_server FOREIGN DATA WRAPPER DFS_FDW OPTIONS ( 
  address 'obs.ap-southeast-1.myhuaweicloud.com', 
   access_key 'xxxxxxxxx', 
  secret_access_key 'yyyyyyyyyyyyy', 
  type 'obs'
);

Create the dli_server server, in which dfs_fdw is the foreign-data wrapper:

1
2
3
4
5
6
7
8
9

CREATE SERVER dli_server FOREIGN DATA WRAPPER DFS_FDW OPTIONS ( 
  address 'obs.ap-southeast-1.myhuaweicloud.com', 
  access_key 'xxxxxxxxx', 
  secret_access_key 'yyyyyyyyyyyyy', 
  type 'dli',
  dli_address 'dli.example.com',
  dli_access_key 'xxxxxxxxx',
  dli_secret_access_key 'yyyyyyyyyyyyy'
);

You are advised to create another server in the homogeneous cluster, where gc_fdw is the foreign data wrapper in the database:

1
2
3
4
5
6

CREATE SERVER server_remote FOREIGN DATA WRAPPER GC_FDW OPTIONS 
   (address '10.10.0.100:25000,10.10.0.101:25000',
  dbname 'test', 
  username 'test', 
  password 'xxxxxxxx'
);

Create a server whose FOREIGN DATA WRAPPER is dist_fdw for importing and exporting text data on OBS.

1
2
3
4
5

CREATE SERVER import_server FOREIGN DATA WRAPPER DIST_FDW OPTIONS 
(
  access_key 'ak_string',
  secret_access_key 'sk_string'
);

Helpful Links

ALTER SERVER DROP SERVER