Message-Id: <018573B2-DC52-4B98-9AB6-1ACB953B0035@zeesource.net>
From: Claire McLister <mclister@zeesource.net>
To: pgsql-performance@postgresql.org
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Subject: JDBC/Stored procedure performance issue
Date: Mon, 28 Jan 2008 09:59:07 -0800

Hi All,

I am experiencing a strange performance issue with Postgresql (7.4.19)  
+ PostGIS. (I posted to the PostGIS list but got no response, so am  
trying here.)

We have a table of entries that contains latitude, longitude values  
and I have a simple query to retrieve all entries within a specified 2- 
D box.

The latitude, longitude are stored as decimals, plus a trigger stores  
the corresponding geometry object.

When I do an EXPLAIN ANALYZE on one query that returns 3261 rows, it  
executes in a reasonable 159ms:

EXPLAIN ANALYZE SELECT DISTINCT latitude, longitude, color FROM  
NewEntries
	 WHERE groupid = 57925 AND
		       location @ SetSRID(MakeBox2D(SetSRID(MakePoint(-123.75,  
36.597889), 4326),
                		                    SetSRID(MakePoint(-118.125,  
40.979898), 4326)), 4326);


Unique  (cost=23.73..23.74 rows=1 width=30) (actual  
time=143.648..156.081 rows=3261 loops=1)
   ->  Sort  (cost=23.73..23.73 rows=1 width=30) (actual  
time=143.640..146.214 rows=3369 loops=1)
         Sort Key: latitude, longitude, color
         ->  Index Scan using group_index on newentries   
(cost=0.00..23.72 rows=1 width=30) (actual time=0.184..109.346  
rows=3369 loops=1)
               Index Cond: (groupid = 57925)
               Filter: ("location" @  
'0103000020E610000001000000050000000000000000F05EC0000000A0874C42400000000000F05EC0000000406D7D44400000000000885DC0000000406D7D44400000000000885DC0000000A0874C42400000000000F05EC0000000A0874C4240 
'::geometry)
Total runtime: 159.430 ms
(7 rows)

If I issue the same query over JDBC or use a PSQL stored procedure, it  
takes over 3000 ms, which, of course is unacceptable!

Function Scan on gettilelocations  (cost=0.00..12.50 rows=1000  
width=30) (actual time=3311.368..3319.265 rows=3261 loops=1)
Total runtime: 3322.529 ms
(2 rows)

The function gettilelocations is defined as:

CREATE OR REPLACE FUNCTION GetTileLocations(Integer, real, real, real,  
real)
    RETURNS SETOF TileLocation
AS
'
    DECLARE
        R TileLocation;
    BEGIN
        FOR R IN SELECT DISTINCT latitude, longitude, color FROM  
NewEntries
            WHERE groupid = $1 AND
                location @ SetSRID(MakeBox2D(SetSRID(MakePoint($2,  
$3), 4326),
                                     SetSRID(MakePoint($4, $5), 4326)),
                   4326) LOOP
            RETURN NEXT R;
        END LOOP;
    RETURN;
    END;
'
LANGUAGE plpgsql STABLE RETURNS NULL ON NULL INPUT;

Can someone please tell me what we are doing wrong? Any help would be  
greatly appreciated.

Thanks

Claire

  --
  Claire McLister                        mclister@zeesource.net
  21060 Homestead Road Suite 150
  Cupertino, CA 95014            408-733-2737(fax)

                      http://www.zeemaps.com