Re: Possible to make SessionPool.acquire() block until connection available?
Jim Freeman <[email protected]>
| Newsgroups | gmane.comp.python.db.cx-oracle |
|---|---|
| Message-ID | <[email protected]> |
Oops, meant to say "Same behavior if I use SPOOL_ATTRVAL_NOWAIT..." in 3rd paragraph below. From: Jim Freeman <[email protected]> To: "cx-oracle-users-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org" <cx-oracle-users-5NWGOfrQmneRv+LV9MX5uuRhgaa4a2kL@public.gmane.orgnet> Sent: Friday, August 1, 2014 3:58 PM Subject: Re: [cx-oracle-users] Possible to make SessionPool.acquire() block until connection available? Thanks Vladimir and Krishna! Using cx_Oracle.SPOOL_ATTRVAL_WAIT causes the behavior I need -- acquire() now blocks until a connection is free. Still one minor issue: say I have 4 threads and a 2 connection pool. In my test app the threads do a block of acquire/sleep/release in a tight loop of N iterations. Threads 3 and 4 get completely starved until Threads 1 and 2 have finished all N iterations. If I put a 1 second sleep after the release, then the connections are fair-shared between the 4 requesters. Same behavior if I use SPOOL_ATTRVAL_WAIT and put a sempahore(2) around the acquire/sleep/release block. That's because there's no fair semaphore (i.e. FIFO) in Python. In my real app, there is lots of other code to execute between connection aquires, so hopefully thread starvation in acquire() won't be a real issue for me. From: Krishna Mohan IV <[email protected]> To: [email protected] Sent: Thursday, July 31, 2014 10:40 PM Subject: Re: [cx-oracle-users] Possible to make SessionPool.acquire() block until connection available? You need to use cx_Oracle.SPOOL_ATTRVAL_WAIT in the call cx_Oracle.SessionPool(user, password, database, min, max, increment[, connectiontype, threaded, getmode=cx_Oracle.SPOOL_ATTRVAL_NOWAIT, homogeneous=True]) The default seems to be NOWAIT. thanks, krishna On 8/1/2014 10:55 AM, Vladimir Ryabtsev wrote: Hello, Jim, > >Did you consider using language synchronization primitives, like threading.Semaphore or multiprocessing.Semaphore? > > >2014-08-01 0:46 GMT+04:00 Jim Freeman <[email protected]>: > >I have an app which has more worker threads than my session pool max setting, because these threads spend most of their time doing wotk other than DB calls. >> >>My problem is when acquire() is called and there are no available connections, a cx_Oracle.DatabaseError is immediately thrown. Ideally I'd like acquire() to block up to some timeout period, and if multiple threads are blocked on acquire(), they received connections in the same order they blocked. >> >>Maybe the way the Oracle DRCP interface works (which I know little about) prevents this? >>------------------------------------------------------------------------------ >>Infragistics Professional >>Build stunning WinForms apps today! >>Reboot your WinForms applications with our WinForms controls. >>Build a bridge from your legacy apps to the future. >>http://pubads.g.doubleclick.net/gampad/clk?id=153845071&iu=/4140/ostg.clktrk >>_______________________________________________ >>cx-oracle-users mailing list >>cx-oracle-users-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org >>https://lists.sourceforge.net/lists/listinfo/cx-oracle-users >> >> > > > >------------------------------------------------------------------------------ Want fast and easy access to all the code in your enterprise? Index and search up to 200,000 lines of code with a free copy of Black Duck Code Sight - the same software that powers the world's largest code search on Ohloh, the Black Duck Open Hub! Try it now. http://p.sf.net/sfu/bds > > >_______________________________________________ cx-oracle-users mailing list cx-oracle-users-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org https://lists.sourceforge.net/lists/listinfo/cx-oracle-users ------------------------------------------------------------------------------ Want fast and easy access to all the code in your enterprise? Index and search up to 200,000 lines of code with a free copy of Black Duck Code Sight - the same software that powers the world's largest code search on Ohloh, the Black Duck Open Hub! Try it now. http://p.sf.net/sfu/bds _______________________________________________ cx-oracle-users mailing list cx-oracle-users-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org https://lists.sourceforge.net/lists/listinfo/cx-oracle-users ------------------------------------------------------------------------------ Want fast and easy access to all the code in your enterprise? Index and search up to 200,000 lines of code with a free copy of Black Duck Code Sight - the same software that powers the world's largest code search on Ohloh, the Black Duck Open Hub! Try it now. http://p.sf.net/sfu/bds _______________________________________________ cx-oracle-users mailing list cx-oracle-users-5NWGOfrQmneRv+LV9MX5urNAH6kLmebB@public.gmane.org.net https://lists.sourceforge.net/lists/listinfo/cx-oracle-users ------------------------------------------------------------------------------ Want fast and easy access to all the code in your enterprise? Index and search up to 200,000 lines of code with a free copy of Black Duck Code Sight - the same software that powers the world's largest code search on Ohloh, the Black Duck Open Hub! Try it now. http://p.sf.net/sfu/bds _______________________________________________ cx-oracle-users mailing list cx-oracle-users-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org https://lists.sourceforge.net/lists/listinfo/cx-oracle-users