>From my possibly naive understanding of the spec, it means quite simply that a message will be delivered guaranteed once and only once; but I somehow do not think that that is quite what you were asking?<div><br><div>The nice part about JMS is that it is only an API spec and says nothing about implementation.</div>
<div>I would have to look into the spec to see what the answer is to the question: "...how do they deal with duplicates..." etc. If I find the time, I shall be happy to look at the odd JMS implementation and see what the various vendors do in cases such as that in question.</div>
<div>What I do know is that one can specify notification for when a message with "guaranteed delivery" simply cannot be delivered, for whatever reason. This can be to the client or, more likely, as a message from the 'server' to those that want to know.</div>
<div><br></div><div>A relatively�unknown�product called Reliable Transaction Router (RTR), architected and developed long ago by DEC and still maintained and developed by HP, warns, when it considers that a message *may* be a duplicate, i.e., has possibly been delivered previously, of the fact. This is also the case when messages are being 'replayed' after a server has been brought down and is now receiving messages which flowed through the network whilst it was down.�<br>
<br></div><div>There is much discussion around the word "guaranteed", the objection being that nothing can be "guaranteed". Of course it cannot, but if we take things to that extent, we may as well give up right away!</div>
<div><br><div class="gmail_quote">On Thu, Aug 5, 2010 at 15:48, Tony Garnock-Jones <span dir="ltr"><<a href="mailto:tonyg@rabbitmq.com">tonyg@rabbitmq.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<div class="im">John Apps wrote:<br>
> The JMS standard offers guaranteed once<br>
<br>
</div>What exactly do they mean by that? In particular, how do they deal with<br>
duplicates? Do they report failure, or silently let a dup through in certain<br>
situations? If you could point me to the part of the spec that sets out the JMS<br>
resolution of these issues, that's be really useful.<br>
<font color="#888888"><br>
Tony<br>
<br>
</font></blockquote></div><br><br clear="all"><br>-- <br>---<br>John Apps<br>(49) 171 869 1813<br>
</div></div>