Why query executed very slow?

[Devil]

Why my query executed very slow?

I fetch by 25 records. The total time query executed is approximate 213 seconds.

But the in plsql developer or toad all records
fetched by 3-6 seconds

DOA 4.0.6.1
Server 10.2.0.2.0
Client 9.2.0.1.0

TOracleDataSet properties:
Unidirectional = True;
QueryAllRecords = False;
ReadBuffer = 25;

Log from Oracle Monitor:
00:56.401 00:08.142 Query.Execute (25 records processed) select .../*my query*/
01:04.633 00:04.186 Query.Next for up to 25 records (25 records processed)
01:08.929 00:08.372 Query.Next for up to 25 records (25 records processed)
01:17.381 00:04.667 Query.Next for up to 25 records (25 records processed)
01:22.188 00:04.577 Query.Next for up to 25 records (25 records processed)
01:26.855 00:07.751 Query.Next for up to 25 records (25 records processed)
01:34.696 00:04.907 Query.Next for up to 25 records (25 records processed)
01:39.684 00:06.970 Query.Next for up to 25 records (25 records processed)
01:46.754 00:07.901 Query.Next for up to 25 records (25 records processed)
01:54.745 00:06.570 Query.Next for up to 25 records (25 records processed)
02:01.415 00:06.359 Query.Next for up to 25 records (25 records processed)
02:07.894 00:09.153 Query.Next for up to 25 records (25 records processed)
02:17.147 00:06.129 Query.Next for up to 25 records (25 records processed)
02:23.346 00:04.186 Query.Next for up to 25 records (25 records processed)
02:27.633 00:07.150 Query.Next for up to 25 records (25 records processed)
02:34.883 00:03.645 Query.Next for up to 25 records (25 records processed)
02:38.718 00:12.248 Query.Next for up to 25 records (25 records processed)
02:51.066 00:07.261 Query.Next for up to 25 records (25 records processed)
02:58.427 00:07.120 Query.Next for up to 25 records (25 records processed)
03:05.647 00:13.129 Query.Next for up to 25 records (25 records processed)
03:18.936 00:09.384 Query.Next for up to 25 records (25 records processed)
03:28.410 00:11.276 Query.Next for up to 25 records (25 records processed)
03:39.776 00:05.688 Query.Next for up to 25 records (25 records processed)
03:45.575 00:12.367 Query.Next for up to 25 records (25 records processed)
03:58.193 00:08.682 Query.Next for up to 25 records (25 records processed)
04:06.985 00:12.208 Query.Next for up to 25 records (25 records processed)
04:19.293 00:14.070 Query.Next for up to 25 records (25 records processed)
04:33.443 00:00.191 Query.Next for up to 25 records (11 records processed)

 

[Devil]

But when ReadBuffer = 100 query executed only 5-6 seconds.

00:48.099 00:03.045 Query.Execute (100 records processed)
00:51.614 00:00.742 Query.Next for up to 100 records (100 records processed)
00:52.866 00:00.842 Query.Next for up to 100 records (100 records processed)
00:54.669 00:00.441 Query.Next for up to 100 records (100 records processed)
00:55.550 00:00.441 Query.Next for up to 100 records (100 records processed)
00:56.492 00:00.640 Query.Next for up to 100 records (100 records processed)
00:57.543 00:00.471 Query.Next for up to 100 records (86 records processed)
00:58.725 00:00.001 Session.LogOff

 

[Devil]

Oh, I'm sorry this problem on the server, it's will be very-very load in this time .