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https://issues.apache.org/jira/browse/SLIDER-600?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14383849#comment-14383849
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Steve Loughran commented on SLIDER-600:
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Requirements
# All existing role histories load without problems; location retained. Old
files will be used for regression testing here.
# backwards compatibility: new histories reloadable by old code. This is hard
to test if the same generated avro classes are used by any copy of the original
code.
# reload histories where a named role is not currently defined. Options: (a)
discard details or (b) save to role history structures, even though there is
not yet any data on them.
# if there are now more roles than in the history, just generate empty history
for them.
# detect changes in name => priority mappings. If the name of a priority has
changed, treat that as a deleted role followed by a new role. Discard prior
history & treat new role as "new".
# treat two roles swapping prorities as a variant of the one above: both roles
have been replaced.
Key point: changing the priority of a role will lose all historical data, as
will changing the name of a role. But added and removed roles, including reuse
of existing role numbers, will be supported by assuming no placement history.
> RoleHistory to support reloads with different # of roles from current set
> -------------------------------------------------------------------------
>
> Key: SLIDER-600
> URL: https://issues.apache.org/jira/browse/SLIDER-600
> Project: Slider
> Issue Type: Sub-task
> Components: appmaster
> Affects Versions: Slider 0.60
> Reporter: Steve Loughran
> Fix For: Slider 2.0.0
>
>
> The role history won't reload historical placement data if the no. of roles
> doesn't match what it saved. It only persists numeric values and can't
> rebuild the information.
> This means if you add a new role to a cluster: no recovery of any previous
> placement
> It could persist the names -> priorities of each role, and reload the
> positions of those roles about which there are currently records, ignoring
> the rest.
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