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This is an automatically generated e-mail. To reply, visit:
https://reviews.apache.org/r/11009/
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(Updated May 8, 2013, 7:30 p.m.)
Review request for qpid, Alan Conway, Gordon Sim, and Justin Ross.
Changes
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This patch uses the existing 32 bit sequence number.
I used a 64 bit sequence number because I was concerned about what would happen
when the sequence number overflowed and wrapped to 0. I thought the logic to
detect gaps when that condition occurred would be tricky. However, Andrew is
quite correct. The existing unisgned 32 bit sequence number works perfectly
with the logic:
if (seqNo - lastSeqNo > 1) even when lastSeqNo is at MAX and seqNo has just
overflowed.
I removed the local bool sequencing and used the setting.sequencing.
I removed the initialization code since I'm now using the existing sequence
number and that is initialized to 0 upon construction.
Description
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The primary purpose of this is to detect when a ring queue overwrites messages.
The client can examine the sequence number and look for gaps which indicate
that messages have been dropped.
To enable, create the queue with the qpid.queue_msg_sequence arg:
std::string addr("my-queue;"
" {create:sender, delete:always,"
" node: {type: queue, x-declare: {arguments:"
" {qpid.queue_msg_sequence:1, qpid.policy_type:ring,
qpid.max_count:4}}}}");
Sender sender = session.createSender(addr);
This enables sequencing when a message is enqueued. Sequence numbers start at 1
and are unsigned 64 bit numbers.
The exchange level sequencing uses "qpid.msg_sequence" as the key.
*** Question *** Should queues use the same key to enable sequencing as
exchanges? "qpid.msg_sequence" The page
https://cwiki.apache.org/qpid/qpid-extensions-to-amqp.html indicates that
qpid.msg_sequence is supported when declaring a queue, but that key was never
supported for queues.
To get the sequence number:
uint64_t seqNo;
seqNo = response.getProperties()["qpid.queue_msg_sequence"];
*** Note ***
I added a uint64 to the queue class. There is an existing message sequence
number for queues. It is a SequenceNumber class.
However, this is a 32 bit number. I was leery of changing that to a 64 bit
number since it is used throughout the broker and not just as a msg counter.
I'm assuming a 32 bit number is not sufficient in this case since "wrapping
around" to zero would complicate the logic of detecting overwritten messages.
There is a public class variable in Queue.h named std::string seqNoKey; It is
unused. My guess is that it was intended for use with the SequenceNumber class.
Can it be removed?
This does not address the issue of persisting the message sequence after a
broker restart. This will be a future issue.
Before committing this, C++ and python tests would need to be added.
This addresses bug QPID-4591.
https://issues.apache.org/jira/browse/QPID-4591
Diffs (updated)
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/trunk/qpid/cpp/src/qpid/broker/Queue.h 1478851
/trunk/qpid/cpp/src/qpid/broker/Queue.cpp 1478851
/trunk/qpid/cpp/src/qpid/broker/QueueSettings.h 1478851
/trunk/qpid/cpp/src/qpid/broker/QueueSettings.cpp 1478851
Diff: https://reviews.apache.org/r/11009/diff/
Testing
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See attached testring.cpp and mm (make script)
They create a ring queue that holds 4 messages with qpid.queue_msg_sequence,
sends enough messages to overflow the queue, and then retrieves the messages.
It outputs the message sequence numbers.
Thanks,
Ernie Allen
