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http://jira.jboss.com/jira/browse/JGRP-717?page=comments#action_12417506 ]
Bela Ban commented on JGRP-717:
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Using xmit_off makes no sense:
[Vladimir]
- Members A and B
- Member B before becoming a member in a view sends a unicast as a part of discovery to A
- In B we create an entry in UNICAST for target A, sequence number 1
- Say a view V without B is first installed at A (remember this is highly concurrent
situation with multiple node startup)
- The new view V installation at A tears down the connection B made to A in UNICAST *and*
TCP !
- B sends a message (say new OOB discovery) with seq number 2 but since the connection at
the TCP level from B to A was we get that "127.0.0.1:7802 failed sending data to
127.0.0.1:7800: java.net.SocketException: Socket closed" but UNICAST at B considers
message 2 to be sent without a hitch ( we do not propagate exception to UNICAST layer)
- Say next time B sends a discovery message it succeeds (that connection table entry is
now removed and a new connection is created)
- The OOB from B will go up the stack at A but no regular message will since we have a
sequence gap.
==> Kaboom! The regular unicast from B to A never gets delivered at A!
Message ordering protocol for TCP unicasts
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Key: JGRP-717
URL:
http://jira.jboss.com/jira/browse/JGRP-717
Project: JGroups
Issue Type: Feature Request
Reporter: Brian Stansberry
Assigned To: Bela Ban
Fix For: 2.7, 2.6.3
With the introduction of a thread pool in the TCP protocol, the ability to relying on
TCP/IP to guarantee ordering of unicast messages is lost. See JGRP-716. Solution is to
add UNICAST to TCP-based stacks that use a thread pool. This is not ideal since UNICAST
adds overhead for reliable transmission (sending ACKs, retaining sent messages for
retransmission) and this overhead is unnecessary with TCP. Request is for a protocol with
the message ordering functionality of UNICAST but without the reliable transmission
features.
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