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Chapter 24. Disk Management

Alternate Locations

It is possible to create a database in a location other than the default location for the installation. Remember that all database access actually occurs through the database backend, so that any location specified must be accessible by the backend.

Alternate database locations are created and referenced by an environment variable which gives the absolute path to the intended storage location. This environment variable must have been defined before the backend was started and must be writable by the postgres administrator account. Any valid environment variable name may be used to reference an alternate location, although using variable name with a prefix of PGDATA is recommended to avoid confusion and conflict with other variables.

Note: In previous versions of Postgres, it was also permissable to use an absolute path name to specify an alternate storage location. The environment variable style of specification is to be preferred since it allows the site administrator more flexibility in managing disk storage. If you prefer using absolute paths, you may do so by defining "ALLOW_ABSOLUTE_DBPATHS" and recompiling Postgres To do this, either add this line

#define ALLOW_ABSOLUTE_DBPATHS 1
     
to the file src/include/config.h, or by specifying
 CFLAGS+= -DALLOW_ABSOLUTE_DBPATHS
     
in your Makefile.custom.

Remember that database creation is actually performed by the database backend. Therefore, any environment variable specifying an alternate location must have been defined before the backend was started. To define an alternate location PGDATA2 pointing to /home/postgres/data, first type

% setenv PGDATA2 /home/postgres/data
    
to define the environment variable to be used with subsequent commands. Usually, you will want to define this variable in the Postgres superuser's .profile or .cshrc initialization file to ensure that it is defined upon system startup. Any environment variable can be used to reference alternate location, although it is preferred that the variables be prefixed with "PGDATA" to eliminate confusion and the possibility of conflicting with or overwriting other variables.

To create a data storage area in PGDATA2, ensure that /home/postgres already exists and is writable by the postgres administrator. Then from the command line, type

% setenv PGDATA2 /home/postgres/data
% initlocation $PGDATA2
Creating Postgres database system directory /home/postgres/data

Creating Postgres database system directory /home/postgres/data/base

    

To test the new location, create a database test by typing

% createdb -D PGDATA2 test
% destroydb test
    
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