Problem with speed using ODP and DataReader

Question

We are developing an application that uses an Oracle database and are having problems trying to optiomise some of the query handling.
The application is written in C#, using Visual Studio, .NET 1.1, ODP 11g, and connects to a 10gR2 database with Locator extensions.
Below is a typical example of the problems we are encountering.
The stored procedure "GET_POLYGONS_IN_AREA" retrieves an ID, a StyleID and the geometry data for all polygons in the area specified by the input paramaters.
The Explain Plan for this shows that the query (when returning about 4000 polygons) should take about 0.4 secs.
(we have improved things by using better indexes or indexed clusters, but this is insignificant compared to the problem below)
Using SQL Developer, the query does indeed typically return under half a second.
However, when trying to access the results via .NET using the OracleDataProvider, things are very different.
The code snippet below calls the stored procedure and uses an OracleDataReader to retrieve the results.
The call to the first read() is timed and the result output, along with the value for the timing returned by the Oracle procedure.
The result is that the same region typically returns:
Time in Oracle: <0.5 secs, Time for the dr.read(): 5 secs!
This performance level is clearly not what we need.
We have inserted the suggested technique for obtaining the rowsize of the ref cursor (which returns 80).
However, adjusting the fetchsize makes almost no difference - even a value of 10000000 still gives the time for the rd.read() over 4 secs.
Help!
Why is dr.read() taking soooo long when the Oracle query does not and, more importantly, how can we speed this up or get round it so we can get good performance?
Richard
SQL stored procedure:
PROCEDURE "GET_POLYGONS_IN_AREA" (
minX IN NUMBER,
minY IN NUMBER,
maxX IN NUMBER,
maxY IN NUMBER,
timeTakenInHundredthSecs OUT NUMBER,
"RETDATA" OUT NOCOPY SYS_REFCURSOR
IS
tableCursor SYS_REFCURSOR;
thisGeom sdo_geometry;
timeBefore BINARY_INTEGER;
timeAfter BINARY_INTEGER;
BEGIN
timeBefore := DBMS_UTILITY.GET_TIME;
OPEN tableCursor FOR
SELECT VERSIONINFO.ID, VERSIONINFO.STYLEID, STYLEDPOLYGON.GEOMETRY
FROM STYLEDPOLYGON , REGIONALINFO, VERSIONINFO
WHERE
sdo_relate(GEOMETRY,
SDO_Geometry(2003,NULL,NULL,
SDO_elem_info_array(1,1003,3),
SDO_ordinate_array(minX,minY,maxX,maxY)),'mask=anyinteract'
) = 'TRUE'
AND STYLEDPOLYGON.ID = REGIONALINFO.POLYGON
AND REGIONALINFOID = VERSIONINFO.ID
AND VERSIONINFO.status = 1
retdata := tableCursor;
timeAfter := DBMS_UTILITY.GET_TIME;
timeTakenInHundredthSecs := time_after - time_before;
DBMS_OUTPUT.PUT_LINE (timeTakenInHundredthSecs );
END "GET_POLYGONS_IN_AREA";
Code to call the procedure:
dbCommand.CommandText = "GET_POLYGONS_IN_AREA";
dbCommand.CommandType = System.Data.CommandType.StoredProcedure;
dbCommand.Parameters.Clear();
dbCommand.Parameters.Add(new OracleParameter("@minX", Oracle.DataAccess.Client.OracleDbType.Decimal));
dbCommand.Parameters.Add(new OracleParameter("@minY", Oracle.DataAccess.Client.OracleDbType.Decimal));
dbCommand.Parameters.Add(new OracleParameter("@maxX", Oracle.DataAccess.Client.OracleDbType.Decimal));
dbCommand.Parameters.Add(new OracleParameter("@maxY", Oracle.DataAccess.Client.OracleDbType.Decimal));
dbCommand.Parameters["@minX"].Value = currentView.MinX;
dbCommand.Parameters["@minY"].Value = currentView.MinY;
dbCommand.Parameters["@maxX"].Value = currentView.MaxX;
dbCommand.Parameters["@maxY"].Value = currentView.MaxY;
dbCommand.Parameters.Add(new OracleParameter("timeTakenInHundredthSecs", Oracle.DataAccess.Client.OracleDbType.Int32)).Direction = System.Data.ParameterDirection.Output;
dbCommand.Parameters.Add(new OracleParameter("RETDATA", Oracle.DataAccess.Client.OracleDbType.RefCursor)).Direction = System.Data.ParameterDirection.Output;
OracleDataReader dr = dbCommand.ExecuteReader();
timeBefore = DateTime.Now;
dr.FetchSize =10000000; // default is 65535
res = dr.Read();
timeAfter = DateTime.Now;
int timeForRead = timeAfter.Subtract(timeBefore).Seconds*1000 + timeAfter.Subtract(timeBefore).Milliseconds;
int timeTaken =10* (int)dbCommand.Parameters["timeTakenInHundredthSecs"].Value;
MessageBox("Time (mS) in Oracle: " + timeTaken.ToString() + ", Time (mS) for dr.read(): " + timeForRead.ToString());
while (res)
// do stuff...
res = dr.Read();
dr.Close();
dr.Dispose();
//-------------------------------------------------------------------------

Answer 1

A few remarks:
1. You fetch 4000 polygons but we don't know how many points these polygons have on average so it is hard to judge if 5 seconds is long or short.
2. You use a variable tableCursor SYS_REFCURSOR in PL/SQL proc and you do
retdata := tableCursor;
I think you can delete tableCursor and you can simply do:
OPEN retdata FOR
SELECT VERSIONINFO.ID, .....
The use of variable tableCursos is unnecessary.
3. It is hard to tell from your results whether the fetching is slow or the query is slow?
Your measurement is skewed.I don't know how you measured the time that sql developer takes to fetch all rows? Normally sql developer doesn't fetch all the rows.
You should create an extra table dummypolygon and do insert into dummypolygon .. select ... where ..sdo_relate... . Now you can measure how long it takes to fetch the 4000 polygons by selecting from this table:
select * from dummypolygon
How long does this take in ODP.NET?
4. Maybe you can speed up the query by using a hint
select /*+ all_rows */ VERSIONINFO.ID ....
5. Maybe you can speed up the query by doing:
OPEN tableCursor FOR
SELECT VERSIONINFO.ID, VERSIONINFO.STYLEID, STYLEDPOLYGON.GEOMETRY
FROM STYLEDPOLYGON , REGIONALINFO, VERSIONINFO
WHERE
sdo_filter(GEOMETRY,
SDO_Geometry(2003,NULL,NULL,
SDO_elem_info_array(1,1003,3),
SDO_ordinate_array(minX,minY,maxX,maxY))) = 'TRUE'
AND STYLEDPOLYGON.ID = REGIONALINFO.POLYGON
AND REGIONALINFOID = VERSIONINFO.ID
AND VERSIONINFO.status = 1;
Be aware, using sdo_filter instead of sdo_relate will give slightly different results but sdo_filter is faster.