Further thoughts on issue BINDINGS-85

[Simon Holdsworth <simon_holdsworth@uk.ibm.com>]

The JMS 1.1 specification has the following
to say about the deliveryMode attribute (Section 4.7, Message Delivery
Mode):

A JMS provider must deliver a NON_PERSISTENT
message at-most-once. This means that it may lose the message, but
it must not deliver it twice.
A JMS provider must deliver a PERSISTENT
message once-and-only-once. This means a JMS provider failure must
not cause it to be lost, and it must not deliver it twice.

So it seems quite reasonable to map
the SCA atMostOnce intent to JMS delivery mode of NON_PERSISTENT, and exactlyOnce
to PERSISTENT, although exactlyOnce is a profile intent that combines atMostOnce
and atLeastOnce, which would imply to me that atLeastOnce maps to a JMS
delivery mode of PERSISTENT.  Although this does make life quite difficult,
because bindings that require exactlyOnce do also require atLeastOnce.

The only question I have left with regards
to removing the deliveryMode attribute as the resolution to this issue
is whether we should mandate in the JMS binding spec a specific mapping
of these intents to deliveryMode values, or remain silent and leave that
interpretation up to the SCA runtime.

If we were to mandate the mapping, then
the resolution to the issue would be to remove the deliveryMode attribute,
and replace the following paragraph in section 5:

Deployers/assemblers can configure NON_PERSISTENT
for @JMSDeliveryMode in order to provide higher performance with a decreased
quality of service. A binding.jms element configured in this way cannot
satisfy the "atLeastOnce" policy intent. The SCA runtime MUST
raise an error for this invalid combination at deployment time.

with:

The JMS delivery mode used to send messages
from a JMS binding instance which requires the atMostOnce intent and not
the atLeastOnce intent MUST be NON_PERSISTENT [BJM5000X]
The JMS delivery mode used to send messages
from a JMS binding instance which requires the atLeastOnce intent MUST
be PERSISTENT [BJM5000Y]

Given the deliveryMode default is PERSISTENT,
we could also say:

The JMS delivery mode used to send messages
from a JMS binding instance which does not require either of these intents
MUST be PERSISTENT [BJM5000Z]

In fact these could all be collapsed
into a single statement:

The JMS delivery mode used to send messages
from a JMS binding instance MUST be NON_PERSISTENT if it requires the atMostOnce
intent and not the atLeastOnce intent, and PERSISTENT otherwise [BJM5000X]

Comments?

Regards, Simon

Simon Holdsworth
STSM, SCA Bindings Architect; Master Inventor; OASIS SCA Bindings TC Chair
MP 211, IBM UK Labs, Hursley Park, Winchester SO21 2JN, UK
Tel +44-1962-815059 (Internal 245059) Fax +44-1962-816898
Internet - Simon_Holdsworth@uk.ibm.com

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