cancel execution of very slow update query

i am running an update query -query1  from sqlplus command prompt
that query is taking long it s running since 3 hours  

so i want to cancel/stop that query and rerun another update query that updates the same column as query1 is updating and which is faster than query1...  
so is it ok if i just cancel execution of query1 using Ctrl-C (more than 1 time if required)
and rerun the new query which is faster?
Or
do i have to contact dba to cancel previous transactions or how do i quit running query1

please help thanks a lot
at999Asked:
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Mark GeerlingsConnect With a Mentor Database AdministratorCommented:
OK, in that case you would safe to "kill" the session running the update.  Oracle doesn't offer us a convenient "cancel" command, especially from outside of the session running the update.  That application may (or may not) support using [Ctrl]-c to try to cancel an update that appears to be stuck.

If that doesn't work, your only options to cancel it are:
1. Do an "alter system kill session ..." command from SQL*Plus
2. Do a database shutdown, and restart.

Note that following either of these commands, there may be some time required for Oracle to rollback the uncommitted portion of the update that had been processed.

Here are the commands I use in SQL*Plus to identify, then "kill" a session.  Either copy these lines into a *.SQL file then run that file from the SQL> prompt, or copy these lines into SQL*Plus directly:

column sid format 9999;
column serial# format 9999999;
column "Logon" format a13;
set verify off;
select s.sid, s.serial#, nvl((select p.spid from v$process p where p.addr = s.paddr),'  ?') "Spid",
substr(s.osuser,instr(s.osuser,'\') +1,14) "OsUser", to_char(s.logon_time,'YYMMDD HH24MISS') "Logon"
from v$session s where s.username = upper('&username')
order by s.logon_time, s.sid;
--
Prompt Enter the "SID" and "SERIAL#" values to cancel a session...
alter system kill session '&SID,&SERIAL' immediate;
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DavidConnect With a Mentor Senior Oracle Database AdministratorCommented:
It depends :)

The common case is that another user has a lock on the table(s) you are querying.  Unless you are watching your session's I/O consumption increase...  Depending upon your Oracle version, try and report back the results:

select event,p1,p2,p3 from sys.v$session_wait
     where wait_time=0 and event='enqueue';

But if you are working in a distributed environment (three-tier web service, for example), a control-C is not going to do the wonderful stuff we remember from client-server days.

You (or your DBA) would find and kill the offending session by its id.
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at999Author Commented:
i am the only one who runs update queries on that table and i have one session opened in toad which just runs sql select queries
and other one in sqlplus from command prompt which i am trying to cancel... pl help
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DavidConnect With a Mentor Senior Oracle Database AdministratorCommented:
Side thoughts:  even if you're developing/testing, it's prudent to add a I/O upper limit to your (default) user profile.  IOW, auto-kill a session that churns out of control.

The kill above should work cleanly.  You have the back-door option to force a SHUTDOWN on the instance if necessary.  With a query, having no redo logs, a shutdown force is feasible.
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