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From "Hiram Chirino" <hi...@hiramchirino.com>
Subject Re: Stomp, acking and prefetchSize
Date Tue, 08 Apr 2008 14:02:49 GMT
On Tue, Apr 8, 2008 at 6:25 AM, Dejan Bosanac <dejan@nighttale.net> wrote:
> The client should send the DISCONNECT command to the broker and wait
>  > for the socket to get
>  > closed by the peer if we wants to ensure that all the previously
>  > transmitted commands are processed by the broker.
>
>
>  I think that's how it was tested (by I'm not sure at the moment). I'll give
>  it a bit more testing to see if maybe there is a bug on the client side.
>
>
>
>  > Yeah this is an known issue.  This might be the best reason to set the
>  > prefetch size down to 1.  Or just set it to 1 by default when using
>  > auto ack.  Even then it's going to auto ack as many messages as it can
>  > fit in the network buffers.  Robust STOMP clients are going to have to
>  > client ACK.
>
>
>  Cool. I'll document it for future reference.
>
>
>  >  - it's harder to make the client work in sync mode, since it has to
>  > >  discard (or buffer) a large number of messages before it find its
>  > >  receipt (which complicate presumably a simple library).
>  >
>  > sync mode?
>
>
>  When you are waiting for receipts...
>  For example, you subscribe to the queue that has 100 messages, read the
>  first message, send ack and try to get a receipt for it, but there is a lot
>  of messages to be read before your receipt gets its turn.
>

Ah I see.  Most clients should send client ACKs async.  Waiting for
response for an ack will only buy you the 'and only once' guarantee
MAYBE.  You can only get true 'and only once' QOS when you do your
business logic in conjunction with ack in XA mode.  Most organizations
are XA adverse (for good reasons) and therefor are willing to accept
duplicate messages (at least once QOS).  So this is why acks are
always sent async.  Hope that made sense.

>
>
>  So far I think prefetchSize=1 would a good default when using auto
>  > ack.. I still don't see why a big prefetch would be a problem with
>  > client ack.
>
>
>  I've implemented easy way to set defaultPrefetch size in PHP client, so I
>  guess all we need is a piece of docs advising users on appropriate values
>  for specific use cases
>
>
>
>
>  Thanks
>  --
>  Dejan Bosanac
>  www.scriptinginjava.net
>



-- 
Regards,
Hiram

Blog: http://hiramchirino.com

Open Source SOA
http://open.iona.com

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