[jboss-jira] [JBoss JIRA] Commented: (JGRP-1009) Prevent merging during JOIN/LEAVE processing
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https://jira.jboss.org/jira/browse/JGRP-1009?page=com.atlassian.jira.plug...
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Bela Ban commented on JGRP-1009:
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Additional problem: when A received responses, if return_entire_cache is true, B and C
will also have returned information about A. We fixed this by having A replace its own
information in the responses with its current view.
However, we could get inconsistent views in this case:
- T1: the view is V5={A,B,C}
- T2: A multicasts a discovery request, and waits for 5 seconds to get all responses
- T3: A broadcasts a new view V6={A,B,C,D} (D joined)
...
- T8: A receives all responses (after 5 seconds). The responses all contain V5. However, A
now replaces the information from itself with V6. Therefore we have inconsistent views and
a merge is started !
Prevent merging during JOIN/LEAVE processing
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Key: JGRP-1009
URL: https://jira.jboss.org/jira/browse/JGRP-1009
Project: JGroups
Issue Type: Task
Reporter: Bela Ban
Assignee: Bela Ban
Fix For: 2.8
- Say we have V1={A,B,C} and D joins
- A multicasts the new view V2={A,B,C,D} to {A,B,C} and sends a it via unicast to D
- At time T1, A and C have V2, but B might still have V1
- At timeT3 B will also have V2
- HOWEVER, *before* T3 (at T2), A's MERGE functionality gets the current views and
discovers the discrepancy
- A will now initiate a merge. This is superfluous because B would have received V2 at T3
(maybe a few ms later) !
This is not incorrect, but we still want to prevent spurious merges.
SOLUTION:
- Turn off merging during view change processing
- This can be done via discarding of MERGE events at GMS during view processing, or by
disabling merging directly in MERGE2, MERGE3, MERGEFAST. The first option looks more
promising, as it requires only 1 hange in GMS
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