Simulation of concurrency using dbms_lock

Hi all

I tried to simulate the CBC lock contention using the ITO table below and select the declaration as well as the dbms_lock package.
create table kill_cpu (n, primary key(n)) organization index 
as 
select rownum n 
from all_objects 
where rownum <= 23 
;
If I'm running under sql statement regardless of the session, this session is not face any problem of lock of CBC (CBC lock wait event chronicle not in session$ v). So I had planned to run this from 10 different sessions sql statement.
SQL Statement.

alter session set "_old_connect_by_enabled" = true;

select count(*) X 
from kill_cpu 
connect by n > prior n 
start with n = 1 
;
But to simulate competitive access, I used code of all sessions with above the SQL below.
declare  
     n1      number(38);  
     m_handle    varchar2(60);  
begin  
    dbms_lock.allocate_unique(  
        lockname    => 'Synchronize',  
        lockhandle  => m_handle  
    );  

     n1 := dbms_lock.request(  
        lockhandle      => m_handle,  
        lockmode        => dbms_lock.x_mode,  
        timeout         => dbms_lock.maxwait,  
        release_on_commit   => true      -- the default is false !!  
    );  

    dbms_output.put_line(n1);  
end;  
/ 
select count(*) X 
from kill_cpu 
connect by n > prior n 
start with n = 1 
;
Steps followed:
Run only of dbms_lock session code 1.
Run dbms_lock code and sql statement to other meeting 2 and 3.
Perform validation of session 1 to start the concurrency.

But here even session 3 waiting for validation of the session 2, so how can I overcome this dependence commit to simulate the simultaneity say for about 10 sessions?

NOTE: These scripts are derived from Jonathan Lewis, so I'm really sorry if I abused his scripts using it.

-Yasser

YasserRACDBA wrote:
Thank you very much Sir... Jonathan I was bit lazy to read your blog.

By the way don't this is the best method to simulate the latch of the CBC? Is there any other better idea? It seems impractical to demonstrate that it is autonomous transactions for approximately 100 simultaneous sessions... help here?

Yasser,

If you want to test the effect of competitive access with 100 simultaneous sessions, you must have 100 concurrent sessions connected, so the locking/unlocking mechanism is ideal for high stress tests. You may think it's a bit difficult to implement - but I have just a shell script that runs through a loop to send a new copy of sqlplus in the background to run a script that ends with an exit. It's easy to start a test, change the number of concurrent copies if necessary; the test also cleared itself at the end because of the output. There are a number of small improvements that make the process simple and tidy (e.g. the loop of shell past the meter of the loop to the SQL script as a parameter that can be included in the names of the output files).

Don't forget, however, that this script is VERY CPU - it is probably unnecessary in the management of more than two copies by UC because the system is going to be stuck on CPU at the time wherever you get to this point. (It is quite a good test if you want to test the effects of lack of processor on the time of synchronization of log file). For a test of "end-user behavior" more realistic you can replace the application with a loop of pl/sql that executes a query to retrieve a line randomly a large table, then sleep for 0.01 seaconds).

Concerning
Jonathan Lewis

Tags: Database

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