ALTER TABLESPACE

Description

Modifies the attributes of a tablespace.

Precautions

• Only the tablespace owner or a user granted with the ALTER permission can run the ALTER TABLESPACE command. System administrators have this permission by default. To modify a tablespace owner, you must be the tablespace owner or system administrator and a member of the new_owner role.
• The ALTER TABLESPACE operation on a row-store table cannot be performed in a transaction block.
• To change the owner, you must also be a direct or indirect member of the new owning role.
  

  If new_owner is the same as old_owner, the current user will not be verified. A message indicating successful ALTER execution is displayed.

Syntax

• The syntax of renaming a tablespace is as follows:

  1 2	ALTER TABLESPACE tablespace_name RENAME TO new_tablespace_name;

  

• The syntax of setting the owner of a tablespace is as follows:

  1 2	ALTER TABLESPACE tablespace_name OWNER TO new_owner;

  

• The syntax of setting the attributes of a tablespace is as follows:

  1 2	ALTER TABLESPACE tablespace_name SET ( { tablespace_option = value } [, ... ] );

  

• The syntax of resetting the attributes of a tablespace is as follows:

  1 2	ALTER TABLESPACE tablespace_name RESET ( { tablespace_option } [, ... ] );

  

• The syntax of setting the quota of a tablespace is as follows:

  1 2	ALTER TABLESPACE tablespace_name RESIZE MAXSIZE { UNLIMITED | 'space_size'};

  

Parameters

• tablespace_name

  Specifies the tablespace to be modified.

  Value range: an existing table name.

• new_tablespace_name

  Specifies the new name of the tablespace. The new name cannot start with PG_.

  Value range: a string. It must comply with the naming convention.

• new_owner

  Specifies the new owner of the tablespace.

  Value range: an existing username

• tablespace_option

  Sets or resets the parameters of a tablespace.

  Value range:

  • seq_page_cost: sets the optimizer to calculate the cost of obtaining disk pages in sequence. The default value is 1.0.
  • random_page_cost: sets the optimizer to calculate the cost of obtaining disk pages in a non-sequential manner. The default value is 4.0.
    

    • The value of random_page_cost is relative to that of seq_page_cost. It is meaningless when the value is equal to or less than the value of seq_page_cost.
    • The prerequisite for the default value 4.0 is that the optimizer uses indexes to scan table data and the hit ratio of table data in the cache is about 90%.
    • If the size of the table data space is smaller than that of the physical memory, decrease the value to a proper level. On the contrary, if the hit ratio of table data in the cache is lower than 90%, increase the value.
    • If random-access memory like SSD is adopted, the value can be decreased to a certain degree to reflect the cost of true random scan.

  Value range: Positive number of the floating-point type.

• RESIZE MAXSIZE

  Resets the maximum size of tablespace.

  Value range:

  • UNLIMITED: No limit is set for the tablespace.
  • Determined by space_size. For details about the format, see CREATE TABLESPACE.
    

    • If the adjusted quota is smaller than the current tablespace usage, the adjustment is successful. You need to decrease the tablespace usage to a value less than the new quota before writing data to the tablespace.

Examples

• Rename a tablespace.

  -- Create a tablespace.
  gaussdb=# CREATE TABLESPACE tbs_data1 RELATIVE LOCATION 'tablespace1/tbs_data1';
  
  -- Rename a tablespace.
  gaussdb=# ALTER TABLESPACE tbs_data1 RENAME TO tbs_data2;
  
  -- Query.
  gaussdb=# \db tbs_data2
              List of tablespaces
     Name    | Owner |       Location        
  -----------+-------+-----------------------
   tbs_data2 | omm   | tablespace1/tbs_data1

• Set the tablespace owner.

  Example:

  -- Create a user.
  gaussdb=# CREATE USER test PASSWORD '********';
  
  -- Change the owner of the tablespace.
  gaussdb=# ALTER TABLESPACE tbs_data2 OWNER TO test;
  
  -- Query.
  gaussdb=# \db tbs_data2
              List of tablespaces
     Name    | Owner |       Location        
  -----------+-------+-----------------------
   tbs_data2 | test  | tablespace1/tbs_data1
  (1 row)

• Set tablespace attributes.
  Example:

  -- Change the value of seq_page_cost.
  gaussdb=# ALTER TABLESPACE tbs_data2 SET (seq_page_cost = 10);
  
  -- Query.
  gaussdb=# SELECT * FROM pg_tablespace WHERE spcname = 'tbs_data2';
    spcname  | spcowner | spcacl |     spcoptions     | spcmaxsize | relative 
  -----------+----------+--------+--------------------+------------+----------
   tbs_data2 |    16778 |        | {seq_page_cost=10} |            | t
  (1 row)

• Reset tablespace attributes.

  -- Reset the value of seq_page_cost to the default value.
  gaussdb=# ALTER TABLESPACE tbs_data2 RESET (seq_page_cost);
  
  -- Query.
  gaussdb=# SELECT * FROM pg_tablespace WHERE spcname = 'tbs_data2';
    spcname  | spcowner | spcacl | spcoptions | spcmaxsize | relative 
  -----------+----------+--------+------------+------------+----------
   tbs_data2 |    16778 |        |            |            | t
  (1 row)

• Set the tablespace limit.

  Example:

  -- Set the maximum size of a tablespace.
  gaussdb=# ALTER TABLESPACE tbs_data2 RESIZE MAXSIZE '10G';
  
  -- Query.
  gaussdb=# SELECT * FROM pg_tablespace WHERE spcname = 'tbs_data2';
    spcname  | spcowner | spcacl | spcoptions | spcmaxsize | relative 
  -----------+----------+--------+------------+------------+----------
   tbs_data2 |    16778 |        |            | 10485760 K | t
  (1 row)
  
  -- Delete the tablespace.
  gaussdb=# DROP TABLESPACE tbs_data2;
  
  -- Delete the user.
  gaussdb=# DROP USER test;

Helpful Links

CREATE TABLESPACE and DROP TABLESPACE