Acknowledgment Modes (Sun Java System Message Queu

Acknowledgment Modes
A session’s acknowledgment mode determines
the way your application handles the exchange of acknowledgment information
when receiving messages from a broker. The JMS specification defines three
possible acknowledgment modes:

In auto-acknowledge mode, the Message Queue client
runtime immediately sends a client acknowledgment for
each message it delivers to the message consumer; it then blocks waiting for
a return broker acknowledgment confirming that the
broker has received the client acknowledgment. This acknowledgment “handshake”
between client and broker is handled automatically by the client runtime,Key Office 2007,
with no need for explicit action on your part.

In client-acknowledge
mode, your client application must explicitly acknowledge the receipt
of all messages. This allows you to defer acknowledgment until after you have
finished processing the message, ensuring that the broker will not delete
it from persistent storage before processing is complete. You can either acknowledge
each message individually or batch multiple messages and acknowledge them
all at once; the client acknowledgment you send to the broker applies to all
messages received since the previous acknowledgment. In either case, as in
auto-acknowledge mode, the session thread blocks after sending the client
acknowledgment, waiting for a broker acknowledgment in return to confirm that
your client acknowledgment has been received.

In dups-OK-acknowledge
mode, the session automatically sends a client acknowledgment each
time it has received a fixed number of messages, or when a fixed time interval
has elapsed since the last acknowledgment was sent. (This fixed batch size
and timeout interval are currently 10 messages and 7 seconds, respectively,
and are not configurable by the client.) Unlike the first two modes described
above, the broker does not acknowledge receipt of the
client acknowledgment, and the session thread does not block awaiting such
return acknowledgment from the broker. This means that you have no way to
confirm that your acknowledgment has been received; if it is lost in transmission,Microsoft Office Professional Plus 2007 Key,
the broker may redeliver the same message more than once. However, because
client acknowledgments are batched and the session thread does not block,
applications that can tolerate multiple delivery of the same message can achieve
higher throughput in this mode than in auto-acknowledge or client-acknowledge
mode.

Message Queue extends the JMS specification by adding a
fourth acknowledgment mode:

In no-acknowledge
mode, your client application does not acknowledge receipt of messages,Windows 7 Professional Product Key,
nor does the broker expect any such acknowledgment. There is thus no guarantee
whatsoever that any message sent by the broker has been successfully received.
This mode sacrifices all reliability for the sake of maximum throughput of
message traffic.

The standard JMS Session interface, defined in package javax.jms, defines static constants for the
first three acknowledgment modes (AUTO_ACKNOWLEDGE, CLIENT_ACKNOWLEDGE, and DUPS_OK_ACKNOWLEDGE), to be used as arguments
to the connection’s createSession method. The constant representing
the fourth mode (NO_ACKNOWLEDGE) is defined in the extended Message Queue version
of the interface,Buy Office 2007 Key, in package com.sun.messaging.jms.
The session method getAcknowledgeMode returns one of these constants:
int ackMode = mySession.getAcknowledgeMode();
switch (ackMode) { case Session.AUTO_ACKNOWLEDGE: /* Code here to handle auto-acknowledge mode */ break; case Session.CLIENT_ACKNOWLEDGE: /* Code here to handle client-acknowledge mode */ break; case Session.DUPS_OK_ACKNOWLEDGE: /* Code here to handle dups-OK-acknowledge mode */ break; case com.sun.messaging.jms.Session.NO_ACKNOWLEDGE: /* Code here to handle no-acknowledge mode */ break; }
Note –
All of the acknowledgment modes discussed above apply to message
consumption. For message production, the broker’s acknowledgment behavior
depends on the message’s delivery mode (persistent or nonpersistent; see Message Header). The broker acknowledges the receipt
of persistent messages,Office 2007 Enterprise,acknowledgment by an agent of an order on goods to, but not of nonpersistent ones; this behavior is not
configurable by the client.

In a transacted
session (see next section), the acknowledgment mode is ignored and all acknowledgment
processing is handled for you automatically by the Message Queue client runtime.
In this case, the getAcknowledgeMode method returns the special
constant Session.SESSION_TRANSACTED.