Help Center> GaussDB> Distributed_2.x> Working with Databases> Creating and Managing Tablespaces

Updated on 2023-10-23 GMT+08:00

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Creating and Managing Tablespaces

Background

The administrator can use tablespaces to control the layout of disks where a database is installed. This has the following advantages:

If the initial disk partition or volume allocated to the database is full and the space cannot be logically increased, you can create and use tablespaces in other partitions until the space is reconfigured.

Tablespaces allow the administrator to distribute data based on the schema of database objects, improving system performance.
- A frequently used index can be placed in a disk having stable performance and high computing speed, such as a solid device.
- A table that stores archived data and is rarely used or has low performance requirements can be placed in a disk with a slow computing speed.

The administrator can use tablespaces to set the maximum available disk space. In this way, when a partition is shared with other data, tablespaces will not occupy excessive space in the partition.
You can use tablespaces to control the disk space occupied by data in a database. If the usage of a disk where a tablespace resides reaches 90%, the database switches to the read-only mode. It switches back to read/write mode when the disk usage becomes less than 90%.
The automatic disk check of the cluster manager (CM) is enabled by default. To enable it, run the following command:
```
gs_guc set -Z cmserver -N all -I all -c " enable_transaction_read_only = on "
```
Restart the database to make the parameter settings take effect.

Each tablespace corresponds to a file system directory. Run the following command to create a tablespace corresponding to /pg_location/mount1/path1 and specify the maximum available space to 500 GB.

      
           -- Create a tablespace.
openGauss=# CREATE TABLESPACE ds_location1 RELATIVE LOCATION '/pg_location/mount1/path1' MAXSIZE '500G';

If MAXSIZE is used to manage tablespace quotas, the concurrent insertion performance may deteriorate by about 30%. MAXSIZE specifies the maximum quota for each each DN. The difference between the actual tablespace capacity of each DN and the specified quota should be within 500 MB. Determine whether to set a tablespace to its maximum size as required.

GaussDB provides two tablespaces: pg_default and pg_global.

Default tablespace pg_default: stores non-shared system catalogs, user tables, user table indexes, temporary tables, temporary table indexes, and internal temporary tables. The corresponding storage directory is the base directory in the instance data directory.
Shared tablespace pg_global: stores shared system tables. The corresponding storage directory is the base directory in the global data directory.

Precautions:

You are not advised to use user-defined tablespaces.
This is because user-defined tablespaces are usually used with storage media other than the main storage (storage device where the default tablespace is located, such as a disk) to isolate I/O resources that can be used by different services. Storage devices use standard configurations and do not have other available storage media in scenarios such as Huawei Cloud. If the user-defined tablespace is not properly used, the system cannot run stably for a long time and the overall performance is affected. Therefore, you are advised to use the default tablespace.

Procedure

Create a tablespace.

Run the following command to create user jack:

        
             openGauss=# CREATE USER jack IDENTIFIED BY 'xxxxxxxxx';

If the following information is displayed, the user has been created:

        
             CREATE ROLE

Run the following command to create a tablespace:

        
             openGauss=# CREATE TABLESPACE fastspace RELATIVE LOCATION 'my_tablespace/tablespace1';

If the following information is displayed, the tablespace has been created:

        
             CREATE TABLESPACE

fastspace is the new tablespace, and CN/DN data directory/pg_location/my_tablespace/tablespace1 is an empty directory on which users have read and write permissions.

A database system administrator can run the following command to grant the permission of accessing the fastspace tablespace to user jack:

        
             openGauss=# GRANT CREATE ON TABLESPACE fastspace TO jack;

If the following information is displayed, the permission has been assigned:

        
             GRANT

Create an object in a tablespace.

If you have the CREATE permission on the tablespace, you can create database objects in the tablespace, such as tables and indexes.

Take creating a table as an example:

Method 1: Run the following command to create a table in a specified tablespace:

       
            openGauss=# CREATE TABLE foo(i int) TABLESPACE fastspace;

If the following information is displayed, the table has been created:

       
            NOTICE: The 'DISTRIBUTE BY' clause is not specified. Using 'i' as the distribution column by default.
HINT: Please use 'DISTRIBUTE BY' clause to specify suitable data distribution column.
CREATE TABLE

Method 2: Use set default_tablespace to set the default tablespace and then create a table:

       
            openGauss=# SET default_tablespace = 'fastspace';
SET
openGauss=# CREATE TABLE foo2(i int);
NOTICE: The 'DISTRIBUTE BY' clause is not specified. Using 'i' as the distribution column by default.
HINT: Please use 'DISTRIBUTE BY' clause to specify suitable data distribution column.
CREATE TABLE

In this example, fastspace is the default tablespace, and foo2 is the created table.

Use one of the following methods to query a tablespace:
- Method 1: Check the pg_tablespace system catalog. Run the following command to view all the tablespaces defined by the system and users:
  1
  
  openGauss=# SELECT spcname FROM pg_tablespace;
- Method 2: Run the following meta-command of the gsql program to query the tablespaces:
```
openGauss=# \db
```

Query the tablespace usage.

Query the current usage of the tablespace.

       
            openGauss=# SELECT PG_TABLESPACE_SIZE('fastspace');

Information similar to the following is displayed:

       
             pg_tablespace_size 
--------------------
            2146304
(1 row)

2146304 is the size of the tablespace, and its unit is byte.

Calculate the tablespace usage.
Tablespace usage = Value of PG_TABLESPACE_SIZE/Size of the disk where the tablespace resides

Modify a tablespace.

Run the following command to rename tablespace fastspace to fspace:

      
           openGauss=# ALTER TABLESPACE fastspace RENAME TO fspace;
ALTER TABLESPACE

Delete a tablespace and related data.

Run the following command to delete user jack:

       
            openGauss=# DROP USER jack CASCADE;
DROP ROLE

Run the following commands to delete tables foo and foo2:

       
            openGauss=# DROP TABLE foo;
openGauss=# DROP TABLE foo2;

If the following information is displayed, the tables have been deleted:

       
            DROP TABLE

Run the following command to delete tablespace fspace:
1 2

openGauss=# DROP TABLESPACE fspace; DROP TABLESPACE
Only the tablespace owner or system administrator can delete a tablespace.