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Re: non-trivial finalize() on AbstractJdbc2Statement

From: Vitalii Tymchyshyn <tivv00(at)gmail(dot)com>
To: Imran <imranbohoran(at)gmail(dot)com>
Cc: Dave Cramer <pg(at)fastcrypt(dot)com>, pgsql-jdbc(at)postgresql(dot)org
Subject: Re: non-trivial finalize() on AbstractJdbc2Statement
Date: 2012-02-13 13:28:18
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Lists: pgsql-jdbc

While it would be better to handle resource closing with reference 
queues, are you sure your client does not leave resources unclosed? As 
for me, driver in finalize should do only work not done because of close 
not have been called correctly.  In other words, your situation may be 
an indication of close not been called, and so driver does required work 
in finalize, so saturating finalize thread.

Best regards, Vitalii Tymchyshyn

13.02.12 15:02, Imran ???????(??):
> Hi Dave
> Thanks for your response. I agree that this might not be widespread. 
> And I haven't seen much mentions around this problem (hitting GC 
> issues due to non-trivial finalize() methods) reported (based on my 
> google searches). However, I guess the existence of it does provide 
> the opportunity for this to happen as we've noticed. IMHO, encouraging 
> clients to use the api as recommended (i.e. closing resources once 
> they are done with them) is better than the driver allowing 
> opportunity for bad things to happen. Or perhaps the driver caters to 
> this kind of situation using WeakReference as oppose to using a 
> non-trivial finalize().
> What are your thoughts?
> Cheers
> -- Imran
> On Mon, Feb 13, 2012 at 12:09 PM, Dave Cramer <pg(at)fastcrypt(dot)com 
> <mailto:pg(at)fastcrypt(dot)com>> wrote:
>     Well this is a typical which is worse case scenario. People leaking
>     resources because they don't explicitly close them, or your case ? I'm
>     not sure which is worse.
>     Given that the driver is being used in many very high throughput sites
>     without this problem, I'm curious as to why nobody else has complained
>     Dave Cramer
>     dave.cramer(at)credativ(dot)ca
>     On Fri, Feb 10, 2012 at 12:39 PM, Imran <imranbohoran(at)gmail(dot)com
>     <mailto:imranbohoran(at)gmail(dot)com>> wrote:
>     > Hello
>     >
>     > We've been having OOM errors in our applications through GC
>     overhead limits
>     > under heave load resources running queries. Inspecting the heap
>     dump, it
>     > appears that the finalizer queue is taken up most of the heap
>     space. Almost
>     > all of the the finalizer objects I've seen seem to have a
>     > jdbc3PreparedStatement object in it. Going through the source
>     code of the
>     > driver I see that the 'AbstractJdbc2Statement' has a non-trivial
>     finalize
>     > method. I guess this explains why these objects end up in the
>     finalizer
>     > queue. Can I clarify the need to having this finalize() method
>     here? It
>     > seems to be calling the close() method of the statement which I
>     would have
>     > thought is the responsibility of the client building a Statement
>     object. Is
>     > there any chance this can be dropped so we don't see these
>     objects ending up
>     > in the finalizer queue under heavy load and the jvm running out
>     of memory
>     > before the GC threads gets around to 'actually' reclaim the memory?
>     >
>     > Also we are using postgres 9.0.4 and the 8.3-604.jdbc3 version
>     of the
>     > postgresql jdbc driver.
>     >
>     > Cheers
>     > -- Imran

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