3.2 Adding Data Files and Temporary Tablespaces for GeoRaster Users

A GeoRaster database is typically very large. For storage and performance reasons, a database schema should use one or more user tablespaces for GeoRaster data storage (avoid using the system tablespace for storing GeoRaster data), and you should add data files to the tablespaces appropriately. If Oracle Automatic Storage Management (Oracle ASM) or a bigfile tablespace is not being used, you should create many data files for each tablespace and distribute the data files on different disks if possible. You also should create data files or alter existing data files, so that they automatically increase in size when more space is needed in the database.

A GeoRaster table can contain a large (potentially almost unlimited) number of GeoRaster objects. A raster data table (RDT) should be used to contain the raster blocks of a limited number of GeoRaster objects, depending on the size of the rasters. In contrast with GeoRaster tables, an RDT should not grow too large, unless partitioning is to be applied. Also, RDTs can be created on different tablespaces, so that the raster blocks are distributed to different disks. (See also Creating the GeoRaster Table and Raster Data Tables.)

A GeoRaster database may use a temporary tablespace for some operations. When compression is involved in GeoRaster operations, particularly for large scale mosaicking operations, some temporary spaces are needed to store intermediate compressed or uncompressed data. If the GeoRaster user does not have a temporary tablespace, the database system temporary tablespace is used. This is not efficient and may slow down the mosaicking and other operations. Therefore, you should always create temporary tablespaces for GeoRaster users. For example:

CONNECT system/<password>; 
CREATE TEMPORARY TABLESPACE geor_temp TEMPFILE 'geor_temp_1.f' SIZE 1G AUTOEXTEND ON; 
ALTER USER <georaster_user> TEMPORARY TABLESPACE geor_temp;

In general, the amount of temporary space needed is limited. However, for large scale mosaicking, if the result is to be compressed, the temporary space needed is equal to the uncompressed image size of the result. Therefore, specify AUTOEXTEND ON when you create temporary tablespaces for GeoRaster users.