The delivery modes supported by the JMS API are PERSISTENT and
NON_PERSISTENT.
A client marks a message as persistent if it feels that the
application will have problems if the message is lost in transit.
A client marks a message as non-persistent if an occasional
lost message is tolerable. Clients use delivery mode to tell a
JMS provider how to balance message transport reliability with throughput.
Delivery mode covers only the transport of the message to its
destination. Retention of a message at the destination until
its receipt is acknowledged is not guaranteed by a PERSISTENT
delivery mode. Clients should assume that message retention
policies are set administratively. Message retention policy
governs the reliability of message delivery from destination
to message consumer. For example, if a client's message storage
space is exhausted, some messages may be dropped in accordance with
a site-specific message retention policy.
A message is guaranteed to be delivered once and only once
by a JMS provider if the delivery mode of the message is
PERSISTENT
and if the destination has a sufficient message retention policy.
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