Deleting rows from very large table

Question

Hello,
I need to delete rows from a large table, but not all of them, so I can't use truncate. The delete condition is based on one column, something like this:
delete from very_large_table where col1=100;
There's an index (valid, B-tree) on col1, but it still goes very slow. Is there any instruction which can help delete rows faster?
Txh in adv.
A.

Answer 1

Your manager doesn't agree to your running an EXPLAIN PLAN? What is his objection? Sounds like the prototypical 'pointy-hair boss'.
Take a look at these:
-- do_explain.sql
spool explain.txt
-- do EXPLAIN PLAN on target queries with current index definitions
truncate table plan_table
set echo on
explain plan for
<insert query here>
set echo off
@get_explain.sql
-- get_explain.sql
set linesize 120
set pagesize 70
column operation     format a25
column query_plan     format a35
column options          format a15
column object_name     format a20
column order           format a12
column opt           format a6
select     lpad(' ',level) || operation "OPERATION",
     options "OPTIONS",
     decode(to_char(id),'0','COST = ' || NVL(to_char(position),'n/a'),object_name) "OBJECT NAME",
     cardinality "rows",     
     substr(optimizer,1,6) "OPT"
from     plan_table
start     with id = 0
connect by prior id = parent_id
There are probably newer, better ways, but this should work with all living versions of Oracle and is something I've had in my back pocket for several years now. It's not actually executing the query or dml in question, just running an explain plan on it.