ALTER SERVER

Function

Adds, modifies, and deletes the definition of a foreign server.

Existing foreign servers can be queried from the pg_foreign_server system catalog.

Precautions

Only the owner of a server or a system administrator can run this statement.

Syntax

• Change the parameters for an external server.

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ALTER SERVER server_name [ VERSION 'new_version' ]
    [ OPTIONS ( {[ ADD | SET | DROP ] option ['value']} [, ... ] ) ];

In OPTIONS, ADD, SET, and DROP are operations to be executed. If these operations are not specified, ADD operations will be performed by default. option and value are corresponding operation parameters.

Currently, only SET is supported on an HDFS server. ADD and DROP are not supported. The syntax for SET and DROP operations is retained for later use.

• Change the owner of an external server.

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ALTER SERVER server_name 
    OWNER TO new_owner;

• Change the name of an external server.

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ALTER SERVER server_name 
    RENAME TO new_name;

• Refresh the HDFS configuration file.

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ALTER SERVER server_name REFRESH OPTIONS;

Parameter Description

• server_name

  Specifies the name of the server to be modified.

• new_version

  Indicates the new version of the server.

• OPTIONS:
  • address

    Specifies the endpoint of the OBS service.

    Specifies the IP address and port number of the primary and standby nodes of the HDFS cluster.

    

    • address is mandatory for HDFS servers. Therefore, ADD and DROP operations are not supported.
    • address only supports IPv4 addresses in dot-decimal notation, and an address string cannot contain spaces. Groups of addresses are separated by commas (,). An IP address and a port number are separated by a colon (:). You are advised to configure two IP address and port pairs in an HDFS cluster. One is used as the socket address of the primary HDFS NameNode and another is used as that of the secondary HDFS NameNode.
    • If the server type is DLI, the address is the OBS address stored on DLI.
  • hdfscfgpath

    Specifies the HDFS cluster configuration file.

    

    • If HDFS is in security mode, hdfscfgpath is mandatory.
    • If you set hdfscfgpath, you can only set one value for path.
  • fed

    Indicates that dfs_fdw is connected to HDFS in federation mode.

    The value rbf indicates that HDFS uses the Router-based Federation (RBF) mode.

    

    This parameter is supported in 8.1.2 or later. In 8.0.0, this parameter is supported only in 8.0.0.10 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

    Indicates the access key (AK) (obtained by users from the OBS page) 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. This parameter is available only when type is OBS.

  • 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. This parameter is available only when type is OBS.

  • 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.

  • region

    Indicates the IP address or domain name of the OBS server. This parameter is available only when type is OBS.

  • 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.

  • 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. This feature is supported only in 8.1.2 or later.

• new_owner

  Indicates the new owner of the server. To change the owner, you must be the owner of the external server and a direct or indirect member of the new owner role, and must have the USAGE permission on the encapsulator of the external server.

• new_name

  Indicates the new name of the server.

• REFRESH OPTIONS

  Refreshes the HDFS configuration file. This command is executed when the configuration file is modified. If this command is not executed, an access error may be reported.

Examples

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

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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'
) ;

Change the IP address of the hdfs_server server.

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ALTER SERVER hdfs_server OPTIONS ( SET address '10.10.0.110:25000,10.10.0.120:25000');

Change the hdfscfgpath of the hdfs_server server.

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ALTER SERVER hdfs_server OPTIONS ( SET hdfscfgpath '/opt/bigdata/hadoop');

Helpful Links

CREATE SERVER DROP SERVER