I have a small application express app. It runs some code that takes about 12 mins to execute. (I don't need any help with that side of things, thanks) but what I'm wondering is if there's a means to get the screen to move on, while that code completes?
I have an "After Submit" Process, this is of type "PL/SQL Code" and under the execution options, I have "After Submit." The code is an anonymous block that does some checks and then executes some stored procedures.
The trigger for this is a "NEXT" button in the app. However, the clicking of the "NEXT" button results in a basic 'hang' effect, while the spinny animation "egg timer" thing just runs and runs until the code runs its course.
Is there a way to get the screen to move forward to the next page whilst the code is executed in the background, and the user doesn't have to wait? Thanks!
Sure; schedule the procedure as a database job. A simple option is to use DBMS_JOB. For example, if you put that code of yours into a stored procedure (let's call it P_SCOUSE), then you'd
declare
l_job number;
begin
dbms_job.submit(job => l_job,
what => p_scouse,
next_date => sysdate,
interval => null);
commit;
end;
The procedure would run in the background, letting you do whatever you want in the Apex application.
Also, check what DBMS_SCHEDULER offers. It is newer than DBMS_JOB, has some additional options, but - as I said - for such a simple thing, DBMS_JOB does the job.
Related
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.
For example I have a code:
BEGIN
BEGIN
-- First Part
call_1_1();
call_1_2();
...
call_1_N();
END;
BEGIN
-- Second Part
call_2_1();
call_2_2();
...
call_2_M();
END;
END;
This code placed at package and running in a job. Execution of this code (job) can be stopped from the outside by stopping the job. Interrupting could crach execution in the middle of the each block. And the question is how secure the execution of the blocks First Part or Second Part when someone interrupting execution from the outside.
Either all the transaction will complete or none of the transaction will complete. Guaranteed. You have to manage your transactions. For example don't commit before the end of the "block" if you want the block to be in one transaction.
Is there anyway one can run async operations in oracle.
Here is my situation:
I have an expensive proc (say it takes 30 mins to run). I have a web-based front-end that controls when this proc to run. I am looking for triggering the running of the proc from the front-end, and not really wait for the proc to complete.i.e., the control should come back to the web application, with a status like say "In progress".
I am specifically looking for a mechanism to get control back to the front-end without waiting for the proc to complete execution.
Thanks in advance,
SK
I'd second OMG Ponies's request for more specifics.
Depending on what you are trying to accomplish, you may want to look into the DBMS_JOBS package. That allows you to submit a job to the database that runs asynchronously. If you want the database to do something computationally expensive in response to a GUI, for example, your front end could execute something like
CREATE OR REPLACE PROCEDURE run_asynchronously( p_some_parameter IN PLS_INTEGER,
p_jobno OUT PLS_INTEGER )
AS
BEGIN
dbms_job.submit( p_jobno,
'BEGIN ' ||
' some_expensive_procedure( ' ||
to_char(p_some_parameter) || ' ); ' ||
'END;' );
RETURN p_jobno;
END;
That would submit a background job to run SOME_EXPENSIVE_PROCEDURE, passing in P_SOME_PARAMETER. The job would not start until the underlying transaction commits which is excellent if SOME_EXPENSIVE_PROCEDURE does something that cannot be rolled back like sending email or FTP-ing a file.
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/