Re: Remove usage of finalizers ?

Am 21.10.2013 um 08:29 schrieb Vitalii Tymchyshyn:

> Long finalized queue means that some of your objects finalizes long. This means that either you don't close some of your statements explicitly or you have different type

Actually this is a false assumption. The finalizer daemon thread has a low priority and can sometimes
not keep up with the most trivial cases. See e.g. http://www.fasterj.com/articles/finalizer1.shtml

And yes, closing statements and other objects (e.g. LOBs) explicitly makes a lot of sense.


> of objects (even if it's small number) that take long time to finalize. Check stack trace of finalized thread.
> As of driver, removing finalize altogether is not good as statements won't be closing implicitly. Possible options are:
> 1) Move processing out of finalizer thread with reference queues.
> 2) Warn when something is implicitly closed to indicate usage problem.

That is what I meant: have 2 drivers:

- one for devlopment that does the warning in the finalizer and the closing, but very loud warning
- one for production where the finalize() methods are gone.

Again: there is no guarantee that a finalize() method is ever called from the JVM. So relying on
it may create bogus results

>
> 20 жовт. 2013 23:33, користувач "Heiko W. Rupp" <hwr@pilhuhn.de> написав:
> Hey,
>
> the other day we ran into a situation where our app ran into a OOME situation on heavy
> load. It turned out that we had around 290k objects on the Finalizer queue, that
> were Statements.
>
> There has been a discussion in the past about finalizers (
> see e.g. around  http://www.postgresql.org/message-id/BCD42993-CB7B-453F-95B4-09E84A956AB0@me.com ).
>
> I understand that Connection objects are supposed implement a finalizer (is that actually true?),
> but here the penalty is not that high, as Connections usually are pooled and are thus long living.
>
> Other JDBC objects like Statements are extremely short lived and the creation rate can be
> on a busy application much higher than the finalization rate (which is what we were seeing).
>
> So I wonder if the driver could be rewritten in a way that either
> - uses no finalizers for the short lived objects
> or
> - exist in 2 flavors: a debug version that does excessive logging in the
>  finalizer if the objects were not yet closed (and stays as is wrt the extra work)
>  and a production version where
>  the finalize() methods are removed, so that the objects do not end up
>  in the finalizer queue and can't pile up under high load.
>
> Developers could then use the devel version and the other driver for production.
>
> Relying on the finalize() method to close/free objects on the PG server is a bad
> idea anyway, as there is no guarantee when finalizers run or if they run at all.
>
>   Thanks
>        Heiko
>
>
> --
> Heiko Rupp   hwr@pilhuhn.de
> Blog: http://pilhuhn.blogspot.com   @pilhuhn
>
>
>
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--
Heiko Rupp   hwr@pilhuhn.de
Blog: http://pilhuhn.blogspot.com   @pilhuhn