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Re: Not closing connections and statements

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On 13.08.16 04.04, Arne Vajhøj wrote:
>> True, but you may get deadlocks with you own statements if locks are
>> still pending. E.g. a pending reader may prevent other updates from
>> proceeding. Some databases also reject more than one open data reader.
>> You may get exceptions at subsequent statements in this case.
>
> I am not sure that I understand the deadlock thing.
>
> SQLTransactionRollbackException like other SQLTransientException can
> be retried.
>
> If the commit was successful then I would expect all locks
> to be released and no SQLTransactionRollbackException.
>
> Am I missing something?

No, but there is only a very small step from not closing a statement to 
not calling rollback. And it is another not too large step to not 
closing data readers. So it is rather likely that pending statements 
keep some DB resources until the GC happens to catch them. Especially if 
an exception (e.g. duplicate key) raises in the middle of a transaction.
At this point there is still no deadlock so far, only tremendously bad 
performance because the dependency on the GC. But if your application 
deals with parallel connections or instances the probability of 
deadlocks is significantly increased.
I have found many SQL based applications that are not free of 
distributed race conditions (involving the database server), especially 
when the DB deals with page locks which widens the locks unexpectedly to 
more or less randomly chosen rows. Who really operates at serializable 
isolation level in a larger application? Mostly these deadlocks are that 
unlikely that it might not even happen once in their life time. 
Introducing larger delays in transactions or locks respectively may 
increase this probability significantly, similarly to the birthday paradox.

As others mentioned it is no big deal for short running, single threaded 
applications, of course. It is usually also no big impact for 
applications without transactional integrity, i.e with auto-commit. 
However, databases without snapshot isolation may run into trouble with 
open data readers too.


Marcel

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Not closing connections and statements Cecil Westerhof <Cecil@decebal.nl> - 2016-08-12 13:59 +0200
  Re: Not closing connections and statements Arne Vajhøj <arne@vajhoej.dk> - 2016-08-12 09:15 -0400
    Re: Not closing connections and statements Arne Vajhøj <arne@vajhoej.dk> - 2016-08-12 09:39 -0400
    Re: Not closing connections and statements Marcel Mueller <news.5.maazl@spamgourmet.org> - 2016-08-12 22:31 +0200
      Re: Not closing connections and statements Arne Vajhøj <arne@vajhoej.dk> - 2016-08-12 22:04 -0400
        Re: Not closing connections and statements Marcel Mueller <news.5.maazl@spamgourmet.org> - 2016-08-13 07:55 +0200
  Re: Not closing connections and statements Martin Gregorie <martin@address-in-sig.invalid> - 2016-08-12 19:01 +0000
    Re: Not closing connections and statements Marcel Mueller <news.5.maazl@spamgourmet.org> - 2016-08-12 22:35 +0200
      Re: Not closing connections and statements Arne Vajhøj <arne@vajhoej.dk> - 2016-08-12 21:52 -0400
    Re: Not closing connections and statements Cecil Westerhof <Cecil@decebal.nl> - 2016-08-12 23:55 +0200
      Re: Not closing connections and statements Eric Sosman <esosman@comcast-dot-net.invalid> - 2016-08-12 18:16 -0400
        Re: Not closing connections and statements Cecil Westerhof <Cecil@decebal.nl> - 2016-08-13 01:19 +0200
          Re: Not closing connections and statements Martin Gregorie <martin@address-in-sig.invalid> - 2016-08-13 00:21 +0000
            Re: Not closing connections and statements Gunter Herrmann <gunter.herrmann@earthlink.net> - 2016-08-17 16:38 -0400
      Re: Not closing connections and statements Arne Vajhøj <arne@vajhoej.dk> - 2016-08-12 21:58 -0400
        Re: Not closing connections and statements Cecil Westerhof <Cecil@decebal.nl> - 2016-08-13 12:50 +0200
      Re: Not closing connections and statements Arne Vajhøj <arne@vajhoej.dk> - 2016-08-12 21:59 -0400
      Re: Not closing connections and statements Marcel Mueller <news.5.maazl@spamgourmet.org> - 2016-08-13 08:47 +0200
        Re: Not closing connections and statements Andreas Leitgeb <avl@logic.at> - 2016-08-13 08:05 +0000
          Re: Not closing connections and statements Cecil Westerhof <Cecil@decebal.nl> - 2016-08-13 12:21 +0200
          Re: Not closing connections and statements Arne Vajhøj <arne@vajhoej.dk> - 2016-08-13 09:54 -0400
        Re: Not closing connections and statements Cecil Westerhof <Cecil@decebal.nl> - 2016-08-13 12:19 +0200
        Re: Not closing connections and statements Arne Vajhøj <arne@vajhoej.dk> - 2016-08-13 10:04 -0400
          log4j RollingFileAppender (was: Not closing connections and statements) Marcel Mueller <news.5.maazl@spamgourmet.org> - 2016-08-14 22:24 +0200
            Re: log4j RollingFileAppender Arne Vajhøj <arne@vajhoej.dk> - 2016-08-14 21:01 -0400
        Re: Not closing connections and statements Arne Vajhøj <arne@vajhoej.dk> - 2016-08-13 11:58 -0400
          logging (was: Not closing connections and statements) Marcel Mueller <news.5.maazl@spamgourmet.org> - 2016-08-14 23:46 +0200
    Re: Not closing connections and statements Arne Vajhøj <arne@vajhoej.dk> - 2016-08-12 21:44 -0400
  Re: Not closing connections and statements Florian Weimer <fw@deneb.enyo.de> - 2016-08-13 16:33 +0200
    Re: Not closing connections and statements Cecil Westerhof <Cecil@decebal.nl> - 2016-08-13 17:34 +0200

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