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. By default, system administrators have the permission. 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:

ALTER TABLESPACE tablespace_name 
    RENAME TO new_tablespace_name;

The syntax of setting the owner of a tablespace is as follows:
```
ALTER TABLESPACE tablespace_name 
    OWNER TO new_owner;
```

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

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

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

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

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

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.

-- 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.

-- 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.

-- 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;