Date between sysdate-50 and sysdate problem

Question

hi,
i have a big big problem and i need some help
I have oracle 8i and 10g databases installed at work. i have a problem with an select statement that brings data from 3 tables.
The select looks like this:
select mms_id, img_id, mms_usr_id as usr_id, mms_pvd_id, mms_data as data
from vsc_mms vm, vsc_image vi, vsc_user vu
     where img_mms_id = mms_id
     and mms_usr_id = usr_id and usr_client_id = cli
     and img_mms_id <> 0
          and mms_status =0
          and mms_data between data_ini and data_end .......is not very important; the joins are made all right. What is important is that:
vsc_mms has aprox. 3.000.000 recordings
vsc_image has, also, aprox. 3.000.000 recordings.
select count(distinct img_date) from vsc_image =657.021
select count(distinct mms_data) from vsc_mms >=600.000
On both tables there are, among other, index on mms_data, img_date.
Now, my data_ini and data_end come from java (user send data_ini and data_end through http:// ) OR i can put this select in a procedure like:
declare
datai date:=to_date('20.01.2006','dd.mm.yyyy');
datae date:=to_date('30.01.2006','dd.mm.yyyy');
......my select ..... and mms_data between data_ini and data_end
the select takes on 8i more than 30 seconds. the same select takes on 10G quite same long time. i also run the select using
and mms_data between sysdate-50 and sysdate and i got the same long time.
Also important: this select brings almost 30 recordings; when the restrictions are too severe and the count(*) =0 the result is brought in 0.01 seconds; outherwise, when count(*) >1, is ruinous.
But, if i put and mms_data between to_date('20.01.2006','dd.mm.yyyy') and to_date('30.01.2006','dd.mm.yyyy'), the response come in 1 seconds or less.
1. Can someone help me and tell me why i got this long time for response when i use sysdate or when receiving data_ini, data_end like parameters from java
2. is it true that for a better usage of a index, the procent of repeatedly recordings has to be small? I mean when i have 600.000 distinct recordings from 3.000.000 is it good or not to use index on that column?
thanks in advance

Answer 1

There can be some difference in how Oracle builds execution plan when
you are using binding variables and explicit values:
SQL> create index idxtbl1 on tbl1(date#);
Index created.
SQL> insert into tbl1 select sysdate-rownum from (select 1 from dual connect by lev
200000 rows created.
SQL> create index idxtbl1 on tbl1(date#);
Index created.
SQL> analyze table tbl1 compute statistics for all indexes;
Table analyzed.
SQL>set autotrace traceonly
SQL> var a1 varchar2(20)
SQL> var a2 varchar2(20)
SQL> select * from tbl1 where date# between to_date('01/01/1900','dd/mm/yyyy')
  2  and to_date('01/01/1901','dd/mm/yyyy');
365 rows selected.
Execution Plan
   0      SELECT STATEMENT Optimizer=ALL_ROWS (Cost=3 Card=365 Bytes=3
          285)
   1    0   INDEX (RANGE SCAN) OF 'IDXTBL1' (INDEX) (Cost=3 Card=365 B
          ytes=3285)
Statistics
          0  recursive calls
          0  db block gets
         28  consistent gets
          0  physical reads
          0  redo size
       6809  bytes sent via SQL*Net to client
        772  bytes received via SQL*Net from client
         26  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
        365  rows processed
SQL> exec :a1 := '01/01/1900'
PL/SQL procedure successfully completed.
SQL> exec :a2 := '01/01/1901'
PL/SQL procedure successfully completed.
SQL> select * from tbl1 where date# between to_date(:a1,'dd/mm/yyyy')
  2  and to_date(:a2,'dd/mm/yyyy');
365 rows selected.
Execution Plan
   0      SELECT STATEMENT Optimizer=ALL_ROWS (Cost=4 Card=495 Bytes=4
          455)
   1    0   FILTER
   2    1     INDEX (RANGE SCAN) OF 'IDXTBL1' (INDEX) (Cost=4 Card=495
           Bytes=4455)
Statistics
          0  recursive calls
          0  db block gets
         28  consistent gets
          0  physical reads
          0  redo size
       6809  bytes sent via SQL*Net to client
        772  bytes received via SQL*Net from client
         26  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
        365  rows processedRgds.