[jboss-jira] [JBoss JIRA] Created: (JGRP-1309) Discovery: max_rank doesn't make any sense

[Bela Ban (JIRA)]

Discovery: max_rank doesn't make any sense
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                 Key: JGRP-1309
                 URL: https://issues.jboss.org/browse/JGRP-1309
             Project: JGroups
          Issue Type: Task
            Reporter: Bela Ban
            Assignee: Bela Ban
             Fix For: 3.0


Discovery.max_rank was originally meant to reduce traffic in the discovery phase: rather than 100 members replying to a discovery request, only the coordinators (max_rank=1) would reply and this would be enough for a joiner to find the coordinator and send it a JOIN request.

However, discovery responses also contain additional information, such as the logical name (if set) and the physical address of a member. This is needed by all members of a cluster, and so everyone should return this information to a new joiner.
Seen under this aspect, max_rank is useless and even conter-productive !
If we have 100 members:
- max_rank=0: we get 100 discovery responses
- max_rank=1 (sets return_entire_cache to true): the coordinator return the entire cache to the joiner (1 unicast / cache entry: 100 unicasts)
- max_rank=2: the coordinator plus the next in line return the entire cache: 200 unicasts
- and so on

The current problem is that ergonomics sets return_entire_cache which - in conjunction with max_rank > 0 - generates even more discovery responses than is max_rank is 0 !

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