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From "Denis Magda (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (IGNITE-2655) AffinityFunction: primary and backup copies in different locations
Date Wed, 01 Jun 2016 13:35:59 GMT

    [ https://issues.apache.org/jira/browse/IGNITE-2655?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15310311#comment-15310311
] 

Denis Magda commented on IGNITE-2655:
-------------------------------------

[~v.pyatkov], I've reviewed your latest changes. Please see my comments in the pull-request.
In short the code can fail or work improperly.

[~yzhdanov], I would use this predicate for backups only, leaving method's signature as is,
considering that the primary is chosen by affinity function before. As you said if someone
needs to control the location of primary he can write his own affinity function and most likely
he will because "partition number" passed to the filter says nothing in regards to where this
partition is physically located.

>> As I side note I would say that we are trying to force our users to do some programming.
Does anyone have any idea on how to do this without code? How about supporting simple string
expressions based on node attributes and/or ip addresses?

Presently I would fully rely on the programmable way because it's flexible and covers all
the cases. If there is a demand for the thing you're talking about we can add an overloaded
method that will except a kind of predicate.

[~dsetrakyan], presently the API is left the same for all the supported affinity function:
{{public void setAffinityBackupFilter(@Nullable IgniteBiPredicate<ClusterNode, List<ClusterNode>>
affinityBackupFilter)}} 

where

the first parameter (ClusterNode) is a node being tested and the second list contains nodes
that are already assigned for a partition (primary is always the first).

> AffinityFunction: primary and backup copies in different locations
> ------------------------------------------------------------------
>
>                 Key: IGNITE-2655
>                 URL: https://issues.apache.org/jira/browse/IGNITE-2655
>             Project: Ignite
>          Issue Type: Bug
>            Reporter: Denis Magda
>            Assignee: Vladislav Pyatkov
>            Priority: Critical
>              Labels: important
>             Fix For: 1.7
>
>
> There is a use case when primary and backup copies have to be located in different racks,
building, cities, etc.
> A simple scenario is the following. When nodes are started they will have either "rack1"
or "rack2" value in their attributes list and we will enforce that the backups won't be selected
among the nodes with the same attribute.
> It should be possible to filter out backups using IP addresses as well.
> Presently rendezvous and fair affinity function has {{backupFilter}} that will work perfectly
for the scenario above but only for cases when number of backups for a cache is equal to 1.
> In case when the number of backups is bigger than one {{backupFilter}} will only guarantee
that the primary is located in different location but will NOT guarantee that all the backups
are spread out across different locations as well.
> So we need to provide an API that will allow to spread the primary and ALL backups copies
across different locations.
> The proposal is to introduce {{AffinityBackupFilter}} with the following method
> {{AffinityBackupFilter.isAssignable(Node n, List<Node> assigned)}}
> Where n - potential backup to check, assigned - list of current partition holders, 1st
is primary
> {{AffinityBackupFilter}} will be set using {{affinity.setAffinityBackupFilter}}.
> {{Affinity.setBackupFilter}} has to be deprecated.



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