kill session[metalink]

kill session[metalink]
Problem Description -------------------

Killing the session will not clear the locks. The session on the remote
database will remain idle waiting for input until the network read times
out. Only then the kill session is processed, and locks are released.


Solution Description
--------------------

Options:
========

You can shutdown and restart the database or use the ORAKILL utility to kill
threads.


Oracle has provided an ORAKILL utility that will kill shadow threads. Each
user's connection is represented by a thread in the Oracle process. If a
user's session is killed, then their Oracle session is killed - not the thread.
Oracle has provided an ORAKILL utility which can be passed a thread ID and will
kill the specified thread.

To make sure you do not kill a background process (which would crash your
database), you must perform a select to ensure you get the correct thread.

---
select p.spid "OS Thread", b.name "Name-User", s.osuser, s.program
from v$process p, v$session s, v$bgprocess b
where p.addr = s.paddr
and p.addr = b.paddr UNION ALL
select p.spid "OS Thread", s.username "Name-User", s.osuser, s.program
from v$process p, v$session s
where p.addr = s.paddr
and s.username is not null;
---

This will list all Shadow processes and backgound processes.
Each shadow process will show the thread ID - this is what must be killed via
the ORAKILL utility.

The kill session behavior is mentioned in the ORACLE7 Server Administrator's
Guide (pg 4-13). It does not explicitly indicate what happens to the session
while it is in the KILLED PSEUDO state. What's happening is that PMON
periodically checks to see if any sessions have been killed.
If it finds one, it attempts to rollback the transaction for that session
(that was in progress when it was killed). The reason this can take a long time is
because PMON may have more than one transaction to rollback at a time
(if other sessions have been killed, or if processes have died etc).
Thus, it may take a while to finally cleanup the killed session and have it
disappear from the session monitor. The system i/o monitor correctly shows
the reads and writes being performed by PMON in order to rollback the
session's transaction.

PMON will not delete the session object itself until the client connected to
that session notices that it has been killed. Therefore, the sequence of
events is:

1) alter system kill session is issued - the STATUS of the session object in
V$SESSION becomes KILLED, its server becomes PSEUDO.

2) PMON cleans up the *resources* allocated to the session
(i.e., rolls back its transaction, releases its locks, etc).

3) the entry in V$SESSION remains there until the client of that session (the
client is the process associated with the OSUSER,MACHINE,PROCESS columns in
the V$SESSION view) tries to do another request.

4) the client attempts another SQL statement and gets back ORA-28.

5) PMON can now remove the entry from V$SESSION.
This behavior is necessary because the client still has pointers to the
session object even though the session has been killed. Therefore, the
object cannot be deleted until the client is no longer pointing at it.
[@more@]

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