3.13 Maintaining Efficient Tablespace Use by GeoRaster Objects
After delete or rollback operations, unused space allocated to a raster data table
is not automatically returned to the underlying tablespace. This could result in wasted
tablespace area. Since GeoRaster databases are usually large, it’s a good practice to
efficiently maintain tablespace usage, particularly when disk space is limited. In
general, you should use the LOB storage format SecureFiles LOBs (SecureFiles) or use
BasicFiles LOBS (BasicFiles) in an automatic segment space management tablespace when
creating RDTs. Then you can explicitly shrink the rasterBlock
LOB
segment or the raster data table by altering the raster data table, so that the table
segment can be compacted and unused LOB segment can be released to the tablespace, as
shown in Example 3-4 and Example 3-5.
Example 3-4 Shrinking a RasterBlock LOB Segment
ALTER TABLE city_images_rdt MODIFY LOB (rasterBlock)(SHRINK SPACE);
Example 3-5 Shrinking a Raster Data Table
ALTER TABLE city_images_rdt ENABLE ROW MOVEMENT; ALTER TABLE city_images_rdt SHRINK SPACE CASCADE;
See shrink_clause
in the ALTER TABLE statement in Oracle Database SQL
Language Reference for more information.
As a good practice, if there will be some temporary GeoRaster objects to be created and used, you can always consider creating temporary GeoRaster tables and RDT tables to hold those GeoRaster objects. Once they are not needed, the temporary GeoRaster and RDT tables can be dropped to release the disk space.
Parent topic: GeoRaster Database Creation and Management