Question related to Oracle's LISTENER

Question

Good morning,
I'm reading the 2 Day DBA document (chances are you know that already).
On page 4-5 it gives instructions on how to stop the listener using EM. I followed the instructions and stopped the listener. That was a complete success :)
I thought that since the listener was now stopped, that new connections to the database could not be made.
To test that thinking, I started SQL*Plus and attempted to log in SYS as sysdba. To my surprise, that worked. I also tried with SCOTT, that worked too.
I thought that if the listener is not up, connections to the database could not be made. My understanding is, the listener is what connects a client process to a corresponding server process.
My questions are:
1. How am I able to connect to the database if the listener is down ?
2. What does the listener really do ? (apparently what I thought it did, isn't what it really does)
This may be important, I have both the host and the client on the same machine.
Thank you for your help (again!) :)
John.

Answer 1

user13266377 wrote:
The listener only serves connections coming from remote machines. If you try to connect locally from the machine where the DB is running, it bypasses the listener.That's not completely correct.
If you do the following:
1. Login to DB server
2. lsnrctl stop
3. sqlplus user/pw@tnsentry
It will fail because the listener is not up.
Example:
C:\>tasklist /FI "IMAGENAME eq oracle.exe"
Image Name                     PID Session Name        Session#    Mem Usage
========================= ======== ================ =========== ============
oracle.exe                    2572 Console                    0    558,204 K
oracle.exe                    2636 Console                    0    659,704 K
C:\>lsnrctl stop
LSNRCTL for 32-bit Windows: Version 11.2.0.1.0 - Production on 18-AUG-2010 08:59
:40
Copyright (c) 1991, 2010, Oracle.  All rights reserved.
Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=XXX.XXX.XXX.XXX)(PORT=15
21)))
The command completed successfully
C:\>sqlplus /@OWALLET_USER
SQL*Plus: Release 11.2.0.1.0 Production on Wed Aug 18 08:59:52 2010
Copyright (c) 1982, 2010, Oracle.  All rights reserved.
ERROR:
ORA-12541: TNS:no listener
Enter user-name:Edited by: Centinul on Aug 18, 2010 9:03 AM