I would like to be able to kill a user's query in Oracle 10.2.0.4 without killing their entire session. This would allow the query to end, but not log that user out of their session, so they can continue making other queries. Is this possible at all? Or is the blunt hammer of killing the session the only way to go about ending a query's execution?
I found a trick. I have no idea how safe this is to play with, but it does work. There is an Oracle event, 10237, which is described as "simulate ^C (for testing purposes)".
You have to have the SID and SERIAL# of the session you want to interrupt.
Call SYS.DBMS_SYSTEM.SET_EV( sid, serial#, 10237, 1, '' ) to activate the event in the target session. Any currently executing statement should be interrupted (receiving "ORA-01013: user requested cancel of current operation"). As long as the event is set, any further statements the session attempts to execute will immediately terminate with the same error.
To deactivate the event, make the same call with the fourth parameter set to "0". The session will then be able to execute statements again.
Note that the target session has to detect that the event is set, which may take time, or may never happen, depending on what it is doing. So you can't just quickly toggle the event on and off. You would need to turn it on, verify that the statement in question has stopped, then turn it off.
Here's some sample code. This is meant to be run as an anonymous block in SQLPlus, with substitution variables "sid" and "serial" defined appropriately. You could turn it into a stored procedure with those as its parameters.
DECLARE
l_status v$session.status%TYPE;
BEGIN
dbms_system.set_ev( &sid, &serial, 10237, 1, '');
LOOP
SELECT status INTO l_status FROM v$session
WHERE sid = &sid and serial# = &serial;
EXIT WHEN l_status='INACTIVE';
END LOOP;
dbms_system.set_ev( &sid, &serial, 10237, 0, '');
END;
I suspect it might be possible since you can do this in TOAD. Whilst a query is running a Cancel dialog comes up which you can hit to stop the query.
How it's implemented I don't know, but would be very interested to find out too.
If you're using java there's the java.sql.Statement cancel() method which is supposed to do this. See here for some notes and limitations...
http://download.oracle.com/docs/cd/B14117_01/java.101/b10979/tips.htm#BACDAICJ
You could look at Resource Limits:
"If a user exceeds a call-level resource limit, then Oracle halts the processing of the statement, rolls back the statement, and returns an error. However, all previous statements of the current transaction remain intact, and the user's session remains connected."
That assumes the reason for cancelling the SQL is a resource limit, rather than it updating the wrong set of rows (for example). I suspect you wouldn't be able to affect currently running SQL through adding a resource limit.
http://download.oracle.com/docs/cd/B19306_01/server.102/b14220/security.htm#i13767
http://download.oracle.com/docs/cd/B19306_01/server.102/b14231/dbrm.htm#i1010776
Ideally the user's application should have the ability to cancel a query (via OCICancel or equivalent).
Otherwise, the best would be to use Resource Manager (if on Oracle EE), you can use DBMS_RESOURCE_MANAGER.SWITCH_CONSUMER_GROUP_FOR_SESS to set the target session to consumer group CANCEL_SQL.
Another hack for cancelling other sessions query, which doesn't work with sqlplus windows client sessions though, would be to send urgent signal to the Oracle process using kill -URG (it's a hack, not for everyday use)
I've written about why it works here:
http://blog.tanelpoder.com/2010/02/17/how-to-cancel-a-query-running-in-another-session/
Related
The sched_hangup doc doesn't mention how to do this, and sched_cancel only works for sched_transfer and sched_broadcast.
sched_cancel needs a task or group ID, and only the latter two set the ID in the session, I tested.
Or is there another way to get the task ID?
Workaround
Couldn't find a solution, but this workaround effectively solved the problem:
Set up sched_transfer to a non-existent extension, which will
result in a hangup with No route, Aborting, unless aborted with
sched_cancel.
Below is a Lua example, but this strategy would work in the dialplan just the same because the sched_* commands are all dialplan applications (i.e., part of mod_dptools).
session:execute("sched_transfer", "+600 9999 XML default")
-- ...
local lsi = session:getVariable("last_sched_id")
session:execute("sched_cancel", tostring(lsi))
Here my first steps with Oracle Advanced Queueing...
Szenario: I have a running application where many, many multiple independ processes report back to a central controller to handle the next steps. Simplified the processes are started via cron or via callback of a just finished process.The callbacks are from remote hosts via http -> php -> DB, basicly one http-call after the process has finished on the remote host.
The complete controller logic was written in pl/sql with a singleton concept in mind, so only one process should execute the controller logic at the same time. In fact in 99% of all calls this is not necessary, but that's not the kind of thing I could change at the moment (nor the architecture in general).
To ensure this there is actually a bad mutex implementation, pseudo-code
$mutex = false;
while( not $mutex )
{
$mutex = getMutex();
if( $mutex )
executeController();
else
sleep(5);
}
Wherein the mutex is a one field table having the values 0 (=> "free") or 1 ( => "busy" )
The result of this "beautiful" contstruction is log-file full of "Hey! Got no mutex! Waiting...". And the more processes wait, the longer they wait with no control of who's next. Sometimes the load gets so heavy that the apache first forks and finally dies...
Solution
So my first "operation" would be to replace the mutex with Oracle Advanced Queueing with the controller as single-consumer. Benefits: No more "busy waiting" within the apache layer, strict first come first serve.
( Because all the DB-Actions take place in the same oracle-schema, this could be achieved with standard-objects, pl/sql-methods as well. But why reinvent the wheel, if there are dbms-packages?)
As far as I read using the listen-feature (polling the queued items) in this context is far better than the registration-feaure (scheduling an action when a message arrives).
Basicly everything works fine, i managed to:
create the message type
create the queue-table
create the queue
start the queue
add USER as subscriber
create a procedure for enqueueing
create a procedure for processing & dequeueing
create a procedure for listening to the queue and calling the "process & dequeue"-function when a message arrives.
Of course the listener shall be active 24/7, so i specified no "wait" time. In general depending on the time of the day he will get "something to do" at least every few minutes, more likely every few seconds, sometimes more.
Now here is my problem (if it actually is a problem), i just wrote it according to the examples i found so far:
CREATE OR REPLACE PROCEDURE demo_aq_listener IS
qlist dbms_aq.aq$_agent_list_t;
agent_w_msg sys.aq$_agent;
BEGIN
qlist(0) := sys.aq$_agent(USER, 'demo_aq_queue', NULL);
LOOP
dbms_aq.listen(agent_list => qlist, agent => agent_w_msg);
DEMO_AQ_DEQUEUE();--process & dequeue
END LOOP;
END;
/
Calling the procedure basically does what i expect: It stays "up" and prosseces the queued messages.
But is this the way to do this? What does it do if there are no queued messages? "Sleeping" within the dbms_aq.listen-routine or "Looping as fast as it can", so that I just have implemented another way of "busy waiting"? Might there be a timeout (maybe on oss-level or elsewhere) i just didn't reach?
Here is the complete code with queue-definition etc.: demo_dbms_aq_with_listener.sql
UPDATE
Through further testing i just realized that it seems, that i got a far greater lack of understanding then i hoped :(
On "execution level" don't using the listener at all and just looping the dequeue function has the same effect: It waits for the first/next message
CREATE OR REPLACE PROCEDURE demo_aq_listener IS
BEGIN
LOOP
DEMO_AQ_DEQUEUE();
END LOOP;
END;
/
At least this is easier to test, calling only
BEGIN
DEMO_AQ_DEQUEUE();
END;
/
Also just waits for the first message. Which leaves me totally confused wether I need the listener at all and if what i'am doing does make any sense at all :(
Conclusion
I don't need the listener at all, because i have a single consumer who can treat all messages in the same way.
But the key/core Question stays the same: Is it ok to keep DBMS_AQ.DEQUEUE on "maybe active waiting" in a loop knowing it'll get messages all day long in short intervalls?
(you'll find DEMO_AQ_DEQUEUE() in linked sql-file above)
Better late than never, everything's fine, it is idle waiting:
1) Whilst the DEQUEUE is in sleep mode (WAIT FOREVER), I can see the session is waiting on the event - "Streams AQ: waiting for messages in the queue", that is an IDLE wait class and not actually consuming ANY resources, correct ?
Correct. It's similar to waiting on a row lock on a table. You just "sit there"
https://asktom.oracle.com/pls/apex/asktom.search?tag=writing-a-stand-alone-application-to-continuously-monitor-a-database-queue-aq
Please suppose that we have a procedure inside a package:
MY_PACKAGE.MY_PROCEDURE
This procedure could be launched from many users.
How can I modify the procedure in order to detect if the procedure is at present running since launched from another user?
What is the safest way to detect it?
Thank you for considering my request.
EDIT 01: "It'll depend on why you need to know if a proc is already running or not" ==> If the procedure is at present running, it WON'T be launched again.
You can use the DBMS_APPLICATION_INFO package for such information.
PROCEDURE MY_PROCEDURE(..) IS
BEGIN
DBMS_APPLICATION_INFO.SET_CLIENT_INFO('MY_PACKAGE.MY_PROCEDURE running');
... All your stuff
DBMS_APPLICATION_INFO.SET_CLIENT_INFO(NULL);
EXCEPTION
WHEN OTHERS THEN
DBMS_APPLICATION_INFO.SET_CLIENT_INFO(NULL);
RAISE;
END MY_PROCEDURE;
In order to check it, you can select V$SESSION View:
SELECT *
FROM v$session
WHERE client_info = 'MY_PACKAGE.MY_PROCEDURE running';
If you get any records then the procedure is running.
Based on what others have mentioned and a quick perusal of the DBMS_LOCK package header it appears that you can use the various DBMS_LOCK routines to accomplish what you're trying to do. If I'm reading the header comments correctly you'd want to call ALLOCATE_UNIQUE to get a handle to a unique, named lock, then you'd call REQUEST with the locking mode set to 'x' (Exclusive) to try to grab the lock. If the REQUEST call returns 0 you can go ahead and run your routine. When done, call RELEASE to make the lock available to the next caller.
Best of luck.
I have a ruby script that needs to run continually on the server. I've daemonized it using the daemon gem, and in my script I have it running in an infinite loop, since the daemon gem handles starting and stopping of the process that kicks off my script. In my script, I start out by setting up my DB instance using the Sequel gem and tiny_tds. Like so:
DB = Sequel.connect(adapter: 'tinytds', host: MSSQLHost, database: MSSQLDatabase, user: MSSQLUser, password: MSSQLPassword)
Then I have a loop do that is my infinite loop. Inside that, I test to see if I have a connection using DB.test_connection and then I query the DB every second or so to check if there is new content using a query such as:
DB['SELECT * FROM dbo.[MyTable]'].all do |row|
# MY logic here
# As part of my logic I test to see if I need to delete this row in the table and if so I use
DB.run('DELETE FROM dbo.[MyTable] WHERE some condition')
end
Then at the end of my logic, just before I loop again, I do:
sleep 1
DB.disconnect
All of this works great for about an hour to an hour and a half with everything checking the table, doing the logic, deleting rows, etc., then it dies and gives me this error message TinyTds::Error: Adaptive Server connection timed out
My question, why is that happening? Do I need to reformat my code in a different way? Why doesn't the DB.test_connection do what it is advertised to do? The documentation on that says it checks for a connection in the connection pool, and uses it if it finds it, and creates a new one otherwise.
Any help would be much appreciated
DB.test_connection just acquires a connection from the connection pool, it doesn't check that the connection is still valid (it must have been valid at one point or it wouldn't be in the pool). There's no way that a connection is still valid without actually sending a query. You can use the connection_validator extension that ships with Sequel if you want to do that automatically.
If you are loading Sequel before forking, you need to make sure you call DB.disconnect before forking, otherwise you can end up with multiple forked processes sharing the same connection, which can cause many different issues.
I finally ended up just putting a rescue statement in there that caught this, and re-ran my line of code to create the DB instance, yes, it puts a warning in my log about already setting that instance, but I guess I could just make that not a contstant an that would go away. Anyway, it appears to be working now, and the times it does timeout, I'm recovering gracefully from those. I just wish I could have figured out why it was/is disconnecting like it is.
Using MS Visual Studio 2008 C++ for Windows 32 (XP brand), I try to construct a POP3 client managed from a modeless dialog box.
Te first step is create a persistent object -say pop3- with all that Boost.asio stuff to do asynchronous connections, in the WM_INITDIALOG message of the dialog-box-procedure. Some like:
case WM_INITDIALOG:
return (iniPop3Dlg (hDlg, lParam));
Here we assume that iniPop3Dlg() create the pop3 heap object -say pointed out by pop3p-. Then connect with the remote server, and a session is initiated with the client’s id and password (USER and PASS commands). Here we assume that the server is in TRANSACTION state.
Then, in response to some user input, the dialog-box-procedure, call the appropriate function. Say:
case IDS_TOTAL: // get how many emails in the server
total (pop3p);
return FALSE;
case IDS_DETAIL: // get date, sender and subject for each email in the server
detail (pop3p);
return FALSE;
Note that total() uses the POP3’s STAT command to get how many emails in the server, while detail() uses two commands consecutively; first STAT to get the total and then a loop with the GET command to retrieve the content of each message.
As an aside: detail() and total() share the same subroutines -the STAT handle routine-, and when finished, both leaves the session as-is. That is, without closing the connection; the socket remains opened an the server in TRANSACTION state.
When any option is selected by the first time, the things run as expected, obtaining the desired results. But when making the second chance, the connection hangs.
A closer inspection show that the first time that the statement
socket_.get_io_service().run();
Is used, never ends.
Note that all asynchronous write and read routines uses the same io_service, and each routine uses socket_.get_io_service().reset() prior to any run()
Not also that all R/W operations also uses the same timer, who is reseted to zero wait after each operation is completed:
dTimer_.expires_from_now (boost::posix_time::seconds(0));
I suspect that the problem is in the io_service or in the timer, and the fact that subsequent executions occurs in a different load of the routine.
As a first approach to my problem, I hope that someone would bring some light in it, prior to a more detailed exposition of the -very few and simple- routines involved.
Have you looked at the asio examples and studied them? There are several asynchronous examples that should help you understand the basic control flow. Pay particular importance to the main event loop started by invoking io_service::run, it's important to understand control is not expected to return to the caller until the io_service has no more remaining work to do.