Release 8.1.5
A67295-01
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| Oracle8i Spatial User's Guide and Reference Release 8.1.5 A67295-01 |
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This chapter contains descriptions of the tuning functions and procedures shown in Table 14-1.
This function calculates the average minimum bounding rectangle (MBR) for all geometries in a layer.
SDO_TUNE.AVERAGE_MBR (layername, width, height)
The function returns the width and height of the average MBR for all geometries in a layer.
Data types for height and width are NUMBER.
This function calculates the average MBR by keeping track of the maximum and minimum X and Y values for all geometries in a layer.
This function estimates the spatial index performance such as query selectivity and window query time for a layer.
SDO_TUNE.ESTIMATE_INDEX_PERFORMANCE (layername, sample_ratio, tiling_level,
num_tiles, window_layer, window_gid, tiling_time, filter_time, query_time)
The function returns a number between 0.0 and 1.0 representing estimated spatial index selectivity. Data type is NUMBER.
The function also returns the estimated tiling time, filter time, and query time. Data type for these variables is NUMBER.
This function estimates the appropriate tiling level to use when indexing with fixed-size tiles.
SDO_TUNE.ESTIMATE_TILING_LEVEL (layername, maxtiles, type_of_estimate)
The function returns an integer representing the level to use when creating a spatial index for the specified layer.
The SDO_ADMIN.POPULATE_INDEX() and SDO_ADMIN.UPDATE_INDEX() procedures are used to create or update the spatial index using fixed-size or hybrid indexing. Store the value returned by the SDO_TUNE.ESTIMATE_TILING_LEVEL() function in the SDO_LEVEL column of the <layername>_SDOLAYER table prior to building the spatial index.
The maxtiles parameter specifies the maximum number of tiles that should be used to define a grid covering the rectangular extent of interest. This extent could be:
SDO_TUNE.EXTENT_OF() procedure)
The code shown in Example 14-1 generates a recommendation based on the extent of the defined coordinate system (-90 to +90 latitude and -180 to +180 longitude). This example returns a level whose tiles are not smaller than one-degree cells.
set serveroutput on declare tiling_level integer; begin tiling_level := mdsys.sdo_tune.estimate_tiling_level('WORLD_CITIES',
360*180, 'LAYER_EXTENT'); dbms_output.put_line('VALUE is '|| tiling_level); end;
For most applications, however, it is more effective to call the SDO_TUNE.ESTIMATE_TILING_LEVEL() function using the ALL_GID_EXTENT estimate type with a maxtiles of 10,000. In Example 14-2, assume the data set consists of block groups for San Francisco and that the <layername>_SDODIM table defines the extent to be one that covers all of California. Because the data set is localized to a small subregion of this extent, ALL_GID_EXTENT is the appropriate estimate type. The recommended tiling level in this case will be such that at most, 10,000 tiles will be required to completely cover the extent of San Francisco block groups.
set serveroutput on declare tiling_level integer; begin tiling_level:= mdsys.sdo_tune.estimate_tiling_level('SF_BLOCK_GROUPS',
10000, 'ALL_GID_EXTENT'); dbms_output.put_line('VALUE is' ,|| tiling_level); end;
The third type of estimate helps determine the tiling level that should be used such that on average, the maxtiles parameter defines the number of tiles to cover the extent of a single geometry in the layer. This estimate type requires the most computation of the three because the bounding rectangle of every geometry is used in calculating the average extent. In Example 14-3, eight tiles on average are used to cover any block group in San Francisco.
set serveroutput on declare tiling_level integer; begin tiling_level := mdsys.sdo_tune.estimate_tiling_level('SF_BLOCK_GROUPS', 8,
'AVG_GID_EXTENT'); dbms_output.put_line('Tiling level value is ' || tiling_level); end;
This function returns the estimated time to tessellate a layer.
SDO_TUNE.ESTIMATE_TILING_TIME (layername, sample_ratio, tiling_level, num_tiles)
This function returns the estimated tiling time in seconds. A return of 0 indicates an error.
Data type is NUMBER.
None.
This function determines the extent of all geometries in a layer.
SDO_TUNE.EXTENT_OF (layername, min_X, max_X, min_Y, max_Y)
This function returns the coordinates of the minimum bounding rectangle for all geometric data in a layer. The data type is NUMBER for the four return values.
None.
This procedure generates statistical histograms based on a layer.
SDO_TUNE.HISTOGRAM_ANALYSIS (layername, result_table, type_of_histogram,
max_value, intervals)
The procedure populates the result table with statistical histograms for a spatial layer.
CREATE TABLE histogram (value NUMBER, count NUMBER);
This function provides the number of geometries of each type stored in the layer.
SDO_TUNE.MIX_INFO (layername)
|
layername |
Specifies the name of the spatial data set layer to examine. |
This function calculates geometry type information for the layer. It returns the number of geometries of different type, as well as the percentages of points, line strings, polygons, and complex geometries.
None.
