Answers

1. SAP System is very slow then what you do?

check these Tx:
SM66 - SYSTEMWIDE WORK PROCESS OVERVIEW
SM51- INSTANCES OVERVIEW
SM50-WORK PROCESS OVERVIEW
SM21-SYSTEM LOGS
ST06 - OS MONITOR
ST03 - WORK LOAD ANALYSIS OF SAP SYSTEM
SMLG -LOGON GROUPRS
AL08 - USERS LOGGED IN ENTIRE R/3 SYSTEM
http://www.teknotree.com/maintek/ebook/SAP/03sams%20teach%20yourself%20sap%20in%2024%20hours%20second%20edition/0672328224/ch16lev1sec3.html

http://www.teknotree.com/maintek/ebook/SAP/03sams%20teach%20yourself%20sap%20in%2024%20hours%20second%20edition/0672328224/ch15lev1sec1.html

Transport is running & running.....(STMS)

Your trasport request keeps on running and running......
Take a look at tables TMSTLOCKR and TMSTLOCKP. These contain list of transports currently running. These do not always clear when a transport has completed.
If they have an entry for your change request then it will need to be removed.

I usually do this at the database level with a SQL statement.

If this does not resolve your problem check that the usr/sap/trans/tmp directory
for a .lob file. If one exists delete this and then rerun the last transport.

SQL Query must be something like this:

delete from XYZ.TMSTLOCKR where TRKORR = 'XXXYYYY'

XXXYYYY - Request Number

XYZ - Owner of the table


How to Check From SAP Level and OS level, that your system is DUAL STACK or SINGLE STACK???

Check your Instance profile in RZ10 for parameters starting 
with jstartup/xxxxx, which means the systems is double 
stack (ABAP + JAVA).

AL11 -> under DVEB* directory J2ee folder is there. If the 
folder available it is a dual stack system

Re: What will u do if a background is running from 2days?

If u like to kill the job then go to.....
SM37->find the job->find job details->find out instance 
number on which job is running.....then
SM51->select the job->select work pross->cancel without core 
            

.