Ok then I missed something.
Whan/Where is the reference-counting you were talking about in your first mail 
happening?

Olivier

-----Original Message-----
From: Rob Godfrey <rob.j.godf...@gmail.com> 
Sent: lundi 17 septembre 2018 14:05
To: users@qpid.apache.org
Subject: Re: [Broker-J] JDBC message store performance

Hi Olivier,

the approach you are attempting will not work for the reasons I described 
previously.  If the message has (for instance) been placed in two durable 
subscription queues (because there are two durable subscriptions) then as soon 
as the message is consumed from the first queue it would be removed from the 
store, leading to problems when the second consumer tries to read the message.

-- Rob

On Mon, 17 Sep 2018 at 11:39, VERMEULEN Olivier <olivier.vermeu...@murex.com>
wrote:

> Hello Rob,
>
> Thanks for the answer.
> I started looking at the code to see if there is something I can do 
> about these 2 commits.
> But before going any further I'd like your input on the below, to see 
> if what I'm trying to do could work or if I'm missing something (which 
> I'm surely are)
>
> https://github.com/apache/qpid-broker-j/compare/master...overmeulen:fe
> ature/jdbc-message-store-commits
>
> Regards,
> Olivier
>
> -----Original Message-----
> From: Rob Godfrey <rob.j.godf...@gmail.com>
> Sent: vendredi 14 septembre 2018 16:06
> To: users@qpid.apache.org
> Cc: AYOUBI Ali <ali.ayo...@murex.com>
> Subject: Re: [Broker-J] JDBC message store performance
>
> On Fri, 14 Sep 2018 at 15:30, VERMEULEN Olivier < 
> olivier.vermeu...@murex.com>
> wrote:
>
> > Hello,
> >
> > We ran a performance test with a bunch of brokers and an Oracle 
> > database to store the messages.
> > We noticed that the database was a bit overloaded with commits.
> > Looking at the logs we saw that sending a message was triggering 1 
> > commit for 3 operations (QPID_QUEUE_ENTRIES, QPID_MESSAGE_METADATA,
> > QPID_MESSAGE_CONTENT) which is what we were expecting but receiving 
> > a message was triggering 2 commits (1 for QPID_QUEUE_ENTRIES and 1 
> > for QPID_MESSAGE_METADATA and QPID_MESSAGE_CONTENT).
> > I debugged a bit the code and saw that in 
> > AbstractVirtualHost.executeTransaction the delete on 
> > QPID_MESSAGE_METADATA and QPID_MESSAGE_CONTENT was defined as a 
> > "post commit" operation, explaining why we have 2 commits.
> > Is it something expected? Do you think we could reduce this to 1 
> > commit when receiving a message?
> >
>
> It's not unexpected - basically the issue is that the broker needs to 
> cope with the possibility that the same message is being stored on 
> multiple queues.  The first commit is deleting the referencing of the 
> message from the given queue.  The second commit is occuring after the 
> message has been definitively removed from the queue, and the store 
> has determined that there are no more references, so it is ok to 
> remove the message.  This is driven by reference-counting of the 
> message, and has historically been a place of many potential race 
> conditions.  I'm sure it is possible to optimise the code in some way, 
> but it may not be "easy".  For the BDB store this doesn't matter as 
> much as the actual synchronisation to disk of these operations is 
> coalesced, obviously this is more of an issue for the JDBC store.
>
> -- Rob
>
>
> >
> > Thanks,
> > Olivier
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