慢速Postgres查询

我不熟悉Postgres和SQL。我创建了以下脚本,它从一个点到最近直线上的投影点绘制一条直线。它在一个小数据集上运行良好,5到10个点具有相同的行数;然而,在60个点和2000行上进行查询,大约需要12个小时。它基于粘贴在下面的最近邻函数以及 http://www.bostongis.com/downloads/pgis_nn.txt

编辑 有关pgis_fn_nn的文件可在 http://www.bostongis.com/PrinterFriendly.aspx?content_name=postgis_nearest_neighbor_generic

缓慢的部分是pgis_fn_nn(…)的实现

1. 我做错了什么?
2. 有什么建议可以让这更快吗?
3. 有什么方法可以改进这两个脚本吗?
4. 如果我想将两个查询合并为一个查询,您有什么建议?

-- this sql script creates a line table that connects points from a point table
-- to the projected points from the nearest line to the point of oritin 

-- delete duplicate tables if they exist
DROP TABLE exploded_roads;
DROP TABLE projected_points;
DROP TABLE lines_from_centroids_to_roads;

-- create temporary exploaded lines table
CREATE TABLE exploded_roads (
 the_geom geometry,
 edge_id  serial
);

-- insert the linestring that are not multistring
INSERT INTO exploded_roads
SELECT the_geom
FROM "StreetCenterLines"
WHERE st_geometrytype(the_geom) = 'ST_LineString';

-- insert the linestrings that need to be converted from multi string
INSERT INTO exploded_roads
SELECT the_geom
FROM (
    SELECT ST_GeometryN(
 the_geom,
 generate_series(1, ST_NumGeometries(the_geom)))
    AS the_geom 
    FROM "StreetCenterLines"
)
AS foo;

-- create projected points table with ids matching centroid table
CREATE TABLE projected_points (
 the_geom  geometry,
 pid  serial,
 dauid  int
);

-- Populate Table
-- code based on Paul Ramsey's site and Boston GIS' NN code
INSERT INTO projected_points(the_geom, dauid)
SELECT DISTINCT ON ("DAUID"::int)
 ( 
  ST_Line_Interpolate_Point(
   (
    SELECT the_geom
    FROM exploded_roads
    WHERE edge_id IN 
     (
      SELECT nn_gid
      FROM pgis_fn_nn(centroids.the_geom, 30000000, 1,10, 'exploded_roads', 'true', 'edge_id', 'the_geom')
     )
   ),
   ST_Line_Locate_Point(
    exploded_roads.the_geom,
    centroids.the_geom
   )
  )
 ),
 (centroids."DAUID"::int)

FROM exploded_roads, fred_city_o6_da_centroids centroids;


-- Create Line tables
CREATE TABLE lines_from_centroids_to_roads (
 the_geom geometry,
 edge_id SERIAL
);


-- Populate Line Table
INSERT INTO lines_from_centroids_to_roads(
SELECT
 ST_MakeLine( centroids.the_geom, projected_points.the_geom )
FROM projected_points, fred_city_o6_da_centroids centroids
WHERE projected_points.dauid = centroids.id
);

pgis_fn_nn 从…起

---LAST UPDATED 8/2/2007 --
CREATE OR REPLACE FUNCTION expandoverlap_metric(a geometry, b geometry, maxe double precision, maxslice double precision)
  RETURNS integer AS
$BODY$
BEGIN
    FOR i IN 0..maxslice LOOP
        IF expand(a,maxe*i/maxslice) && b THEN
            RETURN i;
        END IF;
    END LOOP; 
    RETURN 99999999;
END;
$BODY$
LANGUAGE 'plpgsql' IMMUTABLE;

CREATE TYPE pgis_nn AS
   (nn_gid integer, nn_dist numeric(16,5));

CREATE OR REPLACE FUNCTION _pgis_fn_nn(geom1 geometry, distguess double precision, numnn integer, maxslices integer, lookupset varchar(150), swhere varchar(5000), sgid2field varchar(100), sgeom2field varchar(100))
  RETURNS SETOF pgis_nn AS
$BODY$
DECLARE
    strsql text;
    rec pgis_nn;
    ncollected integer;
    it integer;
--NOTE: it: the iteration we are currently at 
--start at the bounding box of the object (expand 0) and move up until it has collected more objects than we need or it = maxslices whichever event happens first
BEGIN
    ncollected := 0; it := 0;
    WHILE ncollected < numnn AND it <= maxslices LOOP
        strsql := 'SELECT currentit.' || sgid2field || ', distance(ref.geom, currentit.' || sgeom2field || ') as dist FROM ' || lookupset || '  as currentit, (SELECT geometry(''' || CAST(geom1 As text) || ''') As geom) As ref WHERE ' || swhere || ' AND distance(ref.geom, currentit.' || sgeom2field || ') <= ' || CAST(distguess As varchar(200)) || ' AND expand(ref.geom, ' || CAST(distguess*it/maxslices As varchar(100)) ||  ') && currentit.' || sgeom2field || ' AND expandoverlap_metric(ref.geom, currentit.' || sgeom2field || ', ' || CAST(distguess As varchar(200)) || ', ' || CAST(maxslices As varchar(200)) || ') = ' || CAST(it As varchar(100)) || ' ORDER BY distance(ref.geom, currentit.' || sgeom2field || ') LIMIT ' || 
        CAST((numnn - ncollected) As varchar(200));
        --RAISE NOTICE 'sql: %', strsql;
        FOR rec in EXECUTE (strsql) LOOP
            IF ncollected < numnn THEN
                ncollected := ncollected + 1;
                RETURN NEXT rec;
            ELSE
                EXIT;
            END IF;
        END LOOP;
        it := it + 1;
    END LOOP;
END
$BODY$
LANGUAGE 'plpgsql' STABLE;

CREATE OR REPLACE FUNCTION pgis_fn_nn(geom1 geometry, distguess double precision, numnn integer, maxslices integer, lookupset varchar(150), swhere varchar(5000), sgid2field varchar(100), sgeom2field varchar(100))
  RETURNS SETOF pgis_nn AS
$BODY$
    SELECT * FROM _pgis_fn_nn($1,$2, $3, $4, $5, $6, $7, $8);
$BODY$
  LANGUAGE 'sql' STABLE;