Torsten Mielke created AMQ-3965:
-----------------------------------
Summary: Expired msgs not getting acked to broker causing consumer
to fill up its prefetch and not getting more msgs.
Key: AMQ-3965
URL: https://issues.apache.org/jira/browse/AMQ-3965
Project: ActiveMQ
Issue Type: Bug
Components: JMS client
Affects Versions: 5.6.0
Reporter: Torsten Mielke
It is possible to get a consumer stalled and not receiving any more messages
when using optimizeAcknowledge.
Let me illustrate in an example (JUnit test attached).
Suppose a consumer with optimizeAcknowledge and a prefetch of 100 msgs.
The broker's queue contains 105 msg. The first 45 msgs have a very low expiry
time, the remaining don't expiry.
So the first 100 msgs get dispatched to the consumer (due to prefetch=100). Out
of these the first 45 msgs do not get dispatched to consumer code because their
expiry has elapsed by the time that are handled in the client.
{code:title=ActiveMQMessageConsumer.java}
public void dispatch(MessageDispatch md) {
MessageListener listener = this.messageListener.get();
try {
[...]
synchronized (unconsumedMessages.getMutex()) {
if (!unconsumedMessages.isClosed()) {
if (this.info.isBrowser() ||
!session.connection.isDuplicate(this, md.getMessage())) {
if (listener != null && unconsumedMessages.isRunning())
{
ActiveMQMessage message = createActiveMQMessage(md);
beforeMessageIsConsumed(md);
try {
boolean expired = message.isExpired();
if (!expired) {
listener.onMessage(message);
}
afterMessageIsConsumed(md, expired);
{code}
listener.onMessage() above is not called as the msg has expired.
However it will calls into afterMessagesIsConsumed()
{code:title=ActiveMQMessageConsumer.java}
private void afterMessageIsConsumed(MessageDispatch md, boolean
messageExpired) throws JMSException {
[...]
if (messageExpired) {
synchronized (deliveredMessages) {
deliveredMessages.remove(md);
}
stats.getExpiredMessageCount().increment();
ackLater(md, MessageAck.DELIVERED_ACK_TYPE);
{code}
and will remove the expired msg from the deliveredMessages list. It then calls
into ackLater().
However ackLater() only fires an ack back to the broker when the number of
unsent acks has reached 50% of the prefetch value.
{code:title=ActiveMQMessageConsumer.java}
private void ackLater(MessageDispatch md, byte ackType) throws JMSException {
[...]
if ((0.5 * info.getPrefetchSize()) <= (deliveredCounter -
additionalWindowSize)) {
session.sendAck(pendingAck);
{code}
In our example it has not reached that mark (only 45 expired msgs, i.e. 45%).
So the first 45 msgs, which expired before being dispatched, did not cause an
ack being sent to the broker.
Now the next 55 messages get processed. These don't have an expiry so they get
dispatched to consumer code.
After dispatching each msg to the registered application code, we call into
afterMessageIsConsumed() but this time executing a different branch as the msgs
are not expired
{code:title=ActiveMQMessageConsumer.java}
private void afterMessageIsConsumed(MessageDispatch md, boolean messageExpired)
throws JMSException {
[...]
else if (isAutoAcknowledgeEach()) {
if (deliveryingAcknowledgements.compareAndSet(false, true)) {
synchronized (deliveredMessages) {
if (!deliveredMessages.isEmpty()) {
if (optimizeAcknowledge) {
ackCounter++;
if (ackCounter >= (info.getPrefetchSize() *
.65) || (optimizeAcknowledgeTimeOut > 0 && System.currentTimeMillis() >=
(optimizeAckTimestamp + optimizeAcknowledgeTimeOut))) {
MessageAck ack =
makeAckForAllDeliveredMessages(MessageAck.STANDARD_ACK_TYPE);
if (ack != null) {
deliveredMessages.clear();
ackCounter = 0;
session.sendAck(ack);
optimizeAckTimestamp =
System.currentTimeMillis();
}
}
{code}
with optimizeAcknowledge=true we only send an ack back to the broker if either
optimizeAcknowledgeTimeOut has elapsed or the ackCounter has reached 65% of the
prefetch (100).
The timeout will not have kicked in. The ackCounter will be at 55 after
processing the last of 100 prefetched messages which is less than 65% of 100.
So with the last prefetched msg being processed, it will not generate an ack
back to the broker.
As a result, the client has processed all prefetched message and will not get
any new messages dispatched from the broker. The broker has another 5 msgs on
the queue but since it never received an ack from the client, it won't dispatch
any further messages.
The client is stalled.
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