- linkend="postgres-user">). Then from the command line, type
-initlocation PGDATA2
-
- (not initlocation
- $PGDATA2). Then you can restart the server.
-
-
- To create a database within the new location, use the command
-
-CREATE DATABASE name WITH LOCATION 'location';
-
- where location is the environment variable you
- used, PGDATA2 in this example. The createdb
- command has the option -D for this purpose.
-
-
- Databases created in alternative locations can be
- accessed and dropped like any other database.
-
-
-
Destroying a Database
the database with the current user name.)
+
+
+
Tablespaces
+
+ Tablespaces in
PostgreSQL allow database superusers to + define locations in the file system where the files representing
+ database objects can be stored. Once created, a tablespace can be referred
+ to by name when creating database objects.
+
+
+ By using tablespaces, a database administrator can control the disk
+ layout of a
PostgreSQL installation. This is useful in + at least two ways. Firstly, if the partition or volume on which the cluster
+ was initialized runs out of space and cannot be extended logically
+ or otherwise, a tablespace can be created on a different partition
+ and used until the system can be reconfigured.
+
+
+ Secondly, tablespaces allow a database administrator to arrange data
+ locations based on the usage patterns of database objects. For
+ example, an index which is very heavily used can be placed on very fast,
+ highly available disk, such as an expensive solid state device. At the same
+ time a table storing archived data which is rarely used or not performance
+ critical could be stored on a less expensive, slower disk system.
+
+
+ Databases, schemas, tables, indexes and sequences can all be placed in
+ particular tablespaces. To do so, a user with the CREATE
+ privilege on a given tablespace must pass the tablespace name as a
+ parameter to the relevant command. For example, the following creates
+ a table in the tablespace space1:
+CREATE TABLE foo(i int) TABLESPACE space1;
+
+
+
+ The tablespace associated with a database is used to store the system
+ catalogs of that database, as well as any temporary files created by
+ server processes using that database. Furthermore, it is the default
+ tablespace selected for any objects created within the database, if
+ no specific TABLESPACE clause is given when those objects
+ are created. If a database is created without specifying a tablespace
+ for it, it uses the same tablespace as the template database it is copied
+ from.
+
+
+ A schema does not in itself occupy any storage (other than a system
+ catalog entry), so assigning a tablespace to a schema does not in itself
+ do anything. What this actually does is to set a default tablespace
+ for tables, indexes, and sequences later created within the schema. If
+ no tablespace is mentioned when creating a schema, it inherits its
+ default tablespace from the current database.
+
+
+ The default choice of tablespace for an index is the same tablespace
+ already assigned to the table the index is for.
+
+
+ Another way to state the above rules is that when a schema, table, index
+ or sequence is created without specifying a tablespace, the object
+ inherits its logical parent's tablespace. A schema will be created in the
+ current database's tablespace; a table or sequence will be created in the
+ tablespace of the schema it is being created in; an index will be created
+ in the tablespace of the table underlying the index.
+
+
+ Two tablespaces are automatically created by initdb. The
+ pg_global tablespace is used for shared system catalogs. The
+ pg_default tablespace is the default tablespace of the
+ template1 and template0 databases (and, therefore,
+ will be the default tablespace for everything else as well, unless
+ explicit TABLESPACE clauses are used somewhere along the
+ line).
+
+
+ Once created, a tablespace can be used from any database, provided
+ the requesting user has sufficient privilege. This means that a tablespace
+ cannot be dropped until all objects in all databases using the tablespace
+ have been removed.
+
+
+ To simplify the implementation of tablespaces,
+
PostgreSQL makes extensive use of symbolic links. This + means that tablespaces can be used only on systems
+ that support symbolic links.
+
+
+ The directory $PGDATA/pg_tblspc contains symbolic links that
+ point to each of the non-built-in tablespaces defined in the cluster.
+ Although not recommended, it is possible to adjust the tablespace
+ layout by hand by redefining these links. Two warnings: do not do so
+ while the postmaster is running; and after you restart the postmaster,
+ update the pg_tablespace catalog to show the new
+ locations. (If you do not, pg_dump will continue to show
+ the old tablespace locations.)
+
+
+
-
- others
-
-
- Other environment variables may be used to designate alternative
- data storage locations. See for more
- information.
-
-
-
-
projects / postgresql.git / commitdiff