CREATE TABLESPACE

Defines a new tablespace.

Synopsis

CREATE TABLESPACE <tablespace_name>
   [OWNER <user_name>]
   LOCATION '<directory>' 
   [WITH (content<ID_1>='<directory>'[, content<ID_2>='<directory>' ... ] [, <tablespace_option = value [, ... ] ])]

Description

CREATE TABLESPACE registers and configures a new tablespace for your SynxDB system. The tablespace name must be distinct from the name of any existing tablespace in the system. A tablespace is a SynxDB system object (a global object), you can use a tablespace from any database if you have appropriate privileges.

A tablespace allows superusers to define an alternative host file system location where the data files containing database objects (such as tables and indexes) reside.

A user with appropriate privileges can pass a tablespace name to CREATE DATABASE, CREATE TABLE, or CREATE INDEX to have the data files for these objects stored within the specified tablespace.

In SynxDB, the file system location must exist on all hosts including the hosts running the master, standby mirror, each primary segment, and each mirror segment.

Parameters

tablespace_name

The name of a tablespace to be created. The name cannot begin with pg_ or gp_, as such names are reserved for system tablespaces.

user_name

The name of the user who will own the tablespace. If omitted, defaults to the user running the command. Only superusers can create tablespaces, but they can assign ownership of tablespaces to non-superusers.

LOCATION ‘directory’

The absolute path to the directory (host system file location) that will be the root directory for the tablespace. When registering a tablepace, the directory should be empty and must be owned by the SynxDB system user. The directory must be specified by an absolute path name of no more than 100 characters. (The location is used to create a symlink target in the pg_tblspc directory, and symlink targets are truncated to 100 characters when sending to tar from utilities such as pg_basebackup.)

For each segment instance, you can specify a different directory for the tablespace in the WITH clause.

contentID_i=‘directory_i’

The value ID_i is the content ID for the segment instance. directory_i is the absolute path to the host system file location that the segment instance uses as the root directory for the tablespace. You cannot specify the content ID of the master instance (-1). You can specify the same directory for multiple segments.

If a segment instance is not listed in the WITH clause, SynxDB uses the tablespace directory specified in the LOCATION clause.

The restrictions identified for the LOCATION directory also hold for directory_i.

tablespace_option

A tablespace parameter to set or reset. Currently, the only available parameters are seq_page_cost and random_page_cost. Setting either value for a particular tablespace will override the planner’s usual estimate of the cost of reading pages from tables in that tablespace, as established by the configuration parameters of the same name (see seq_page_cost, random_page_cost). This may be useful if one tablespace is located on a disk which is faster or slower than the remainder of the I/O subsystem.

Notes

Because CREATE TABLESPACE creates symbolic links from the pg_tblspc directory in the master and segment instance data directory to the directories specified in the command, SynxDB supports tablespaces only on systems that support symbolic links.

CREATE TABLESPACE cannot be run inside a transaction block.

When creating tablespaces, ensure that file system locations have sufficient I/O speed and available disk space.

CREATE TABLESPACE creates symbolic links from the pg_tblspc directory in the master and segment instance data directory to the directories specified in the command.

The system catalog table pg_tablespace stores tablespace information. This command displays the tablespace OID values, names, and owner.

SELECT oid, spcname, spcowner FROM pg_tablespace;

The SynxDB built-in function gp_tablespace_location(tablespace\_oid) displays the tablespace host system file locations for all segment instances. This command lists the segment database IDs and host system file locations for the tablespace with OID 16385.

SELECT * FROM gp_tablespace_location(16385)

Note SynxDB does not support different tablespace locations for a primary-mirror pair with the same content ID. It is only possible to configure different locations for different content IDs. Do not modify symbolic links under the pg_tblspc directory so that primary-mirror pairs point to different file locations; this will lead to erroneous behavior.

Examples

Create a new tablespace and specify the file system location for the master and all segment instances:

CREATE TABLESPACE mytblspace LOCATION '/gpdbtspc/mytestspace';

Create a new tablespace and specify a location for segment instances with content ID 0 and 1. For the master and segment instances not listed in the WITH clause, the file system location for the tablespace is specified in the LOCATION clause.

CREATE TABLESPACE mytblspace LOCATION '/gpdbtspc/mytestspace' WITH (content0='/temp/mytest', content1='/temp/mytest');

The example specifies the same location for the two segment instances. You can a specify different location for each segment.

Compatibility

CREATE TABLESPACE is a SynxDB extension.

SynxDB 2 Documentation