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https://jira.jboss.org/jira/browse/JGRP-1090?page=com.atlassian.jira.plug...
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Bela Ban commented on JGRP-1090:
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[Email from Brian]
I saw JGRP-1090 today an it reminded me of something I was thinking
about back in Sept.
On the receiver side, when a bundled message comes in, a single pool
thread unpacks it and then loops carrying each individual message up
the stack.
I wonder if you can get some strange effects from that under load.
E.g. sender A sends bundle 1 and then bundle 2. On receiver B, thread
1 is processing bundle 1 when bundle 2 comes in and gets handled by
thread 2. As a result, bundle 2 messages start arriving in NAKACK
before a bunch of bundle 1 messages, leading to extra retransmission
tasks.
Problem is worse if thread 1 happens to block a bit above NAKACK.
A possibility is to unpack the bundled message and then resubmit each
individual message to the pool. But I suspect that would cost more
than it gains.
TBH, I doubt this is a big issue, but wanted to throw it out there in
case it sparks any thoughts on your end.
Many retransmissions with message bundling and OOB messages
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Key: JGRP-1090
URL:
https://jira.jboss.org/jira/browse/JGRP-1090
Project: JGroups
Issue Type: Task
Reporter: Bela Ban
Assignee: Bela Ban
Fix For: 2.9
When message bundling is enabled, we queue *regular* messages until max_bundle_size has
been reached or max_bundle_timeout has exceeded.
The problem is that - when sending OOB (as opposed to regular) messages - they're
*not* queued. This means the OOB message is possibly received *before* the regular
messages and thus causes retransmission !
E.g. we send regular message 1-10, then OOB message 11.
Say 1-3 are sent immediately (because the bundle timeout kicked in or the size was
exceeded). Messages 4-10 are queued and sent later. Message 11 is sent immediately.
On the receiver side, message reception could be for example: 1-3, 11, 4-10
When OOB message 11 is received, the receiver asks for retransmission of messages 4-10 !
This is not incorrect, but causes a lot of unneeded retransmissions !
public static void main(String[] args) throws Exception {
JChannel c1=new JChannel("/home/bela/fast.xml");
c1.connect("bla3");
JChannel c2=new JChannel("/home/bela/fast.xml");
c2.connect("bla3");
for(int i=1; i <= 20; i++) {
c1.send(null, null, "hello-" + i);
}
Message oob_msg=new Message(null, null, "oob msg");
oob_msg.setFlag(Message.OOB);
c1.send(oob_msg);
Util.sleep(20000);
Util.close(c2, c1);
}
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